1 /*
   2  * CDDL HEADER START
   3  *
   4  * The contents of this file are subject to the terms of the
   5  * Common Development and Distribution License (the "License").
   6  * You may not use this file except in compliance with the License.
   7  *
   8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   9  * or http://www.opensolaris.org/os/licensing.
  10  * See the License for the specific language governing permissions
  11  * and limitations under the License.
  12  *
  13  * When distributing Covered Code, include this CDDL HEADER in each
  14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  15  * If applicable, add the following below this CDDL HEADER, with the
  16  * fields enclosed by brackets "[]" replaced with your own identifying
  17  * information: Portions Copyright [yyyy] [name of copyright owner]
  18  *
  19  * CDDL HEADER END
  20  */
  21 
  22 /*
  23  * Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
  24  * Copyright 2011 Nexenta Systems, Inc. All rights reserved.
  25  * Copyright 2016 Joyent, Inc.
  26  * Copyright (c) 2014 by Delphix. All rights reserved.
  27  */
  28 
  29 /* This file contains all TCP input processing functions. */
  30 
  31 #include <sys/types.h>
  32 #include <sys/stream.h>
  33 #include <sys/strsun.h>
  34 #include <sys/strsubr.h>
  35 #include <sys/stropts.h>
  36 #include <sys/strlog.h>
  37 #define _SUN_TPI_VERSION 2
  38 #include <sys/tihdr.h>
  39 #include <sys/suntpi.h>
  40 #include <sys/xti_inet.h>
  41 #include <sys/squeue_impl.h>
  42 #include <sys/squeue.h>
  43 #include <sys/tsol/tnet.h>
  44 
  45 #include <inet/common.h>
  46 #include <inet/ip.h>
  47 #include <inet/tcp.h>
  48 #include <inet/tcp_impl.h>
  49 #include <inet/tcp_cluster.h>
  50 #include <inet/proto_set.h>
  51 #include <inet/ipsec_impl.h>
  52 
  53 /*
  54  * RFC7323-recommended phrasing of TSTAMP option, for easier parsing
  55  */
  56 
  57 #ifdef _BIG_ENDIAN
  58 #define TCPOPT_NOP_NOP_TSTAMP ((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) | \
  59         (TCPOPT_TSTAMP << 8) | 10)
  60 #else
  61 #define TCPOPT_NOP_NOP_TSTAMP ((10 << 24) | (TCPOPT_TSTAMP << 16) | \
  62         (TCPOPT_NOP << 8) | TCPOPT_NOP)
  63 #endif
  64 
  65 /*
  66  *  PAWS needs a timer for 24 days.  This is the number of ticks in 24 days
  67  */
  68 #define PAWS_TIMEOUT    ((clock_t)(24*24*60*60*hz))
  69 
  70 /*
  71  * Since tcp_listener is not cleared atomically with tcp_detached
  72  * being cleared we need this extra bit to tell a detached connection
  73  * apart from one that is in the process of being accepted.
  74  */
  75 #define TCP_IS_DETACHED_NONEAGER(tcp)   \
  76         (TCP_IS_DETACHED(tcp) &&        \
  77             (!(tcp)->tcp_hard_binding))
  78 
  79 /*
  80  * Steps to do when a tcp_t moves to TIME-WAIT state.
  81  *
  82  * This connection is done, we don't need to account for it.  Decrement
  83  * the listener connection counter if needed.
  84  *
  85  * Decrement the connection counter of the stack.  Note that this counter
  86  * is per CPU.  So the total number of connections in a stack is the sum of all
  87  * of them.  Since there is no lock for handling all of them exclusively, the
  88  * resulting sum is only an approximation.
  89  *
  90  * Unconditionally clear the exclusive binding bit so this TIME-WAIT
  91  * connection won't interfere with new ones.
  92  *
  93  * Start the TIME-WAIT timer.  If upper layer has not closed the connection,
  94  * the timer is handled within the context of this tcp_t.  When the timer
  95  * fires, tcp_clean_death() is called.  If upper layer closes the connection
  96  * during this period, tcp_time_wait_append() will be called to add this
  97  * tcp_t to the global TIME-WAIT list.  Note that this means that the
  98  * actual wait time in TIME-WAIT state will be longer than the
  99  * tcps_time_wait_interval since the period before upper layer closes the
 100  * connection is not accounted for when tcp_time_wait_append() is called.
 101  *
 102  * If upper layer has closed the connection, call tcp_time_wait_append()
 103  * directly.
 104  *
 105  */
 106 #define SET_TIME_WAIT(tcps, tcp, connp)                         \
 107 {                                                               \
 108         (tcp)->tcp_state = TCPS_TIME_WAIT;                   \
 109         if ((tcp)->tcp_listen_cnt != NULL)                   \
 110                 TCP_DECR_LISTEN_CNT(tcp);                       \
 111         atomic_dec_64(                                          \
 112             (uint64_t *)&(tcps)->tcps_sc[CPU->cpu_seqid]->tcp_sc_conn_cnt); \
 113         (connp)->conn_exclbind = 0;                          \
 114         if (!TCP_IS_DETACHED(tcp)) {                            \
 115                 TCP_TIMER_RESTART(tcp, (tcps)->tcps_time_wait_interval); \
 116         } else {                                                \
 117                 tcp_time_wait_append(tcp);                      \
 118                 TCP_DBGSTAT(tcps, tcp_rput_time_wait);          \
 119         }                                                       \
 120 }
 121 
 122 /*
 123  * If tcp_drop_ack_unsent_cnt is greater than 0, when TCP receives more
 124  * than tcp_drop_ack_unsent_cnt number of ACKs which acknowledge unsent
 125  * data, TCP will not respond with an ACK.  RFC 793 requires that
 126  * TCP responds with an ACK for such a bogus ACK.  By not following
 127  * the RFC, we prevent TCP from getting into an ACK storm if somehow
 128  * an attacker successfully spoofs an acceptable segment to our
 129  * peer; or when our peer is "confused."
 130  */
 131 static uint32_t tcp_drop_ack_unsent_cnt = 10;
 132 
 133 /*
 134  * To protect TCP against attacker using a small window and requesting
 135  * large amount of data (DoS attack by conuming memory), TCP checks the
 136  * window advertised in the last ACK of the 3-way handshake.  TCP uses
 137  * the tcp_mss (the size of one packet) value for comparion.  The window
 138  * should be larger than tcp_mss.  But while a sane TCP should advertise
 139  * a receive window larger than or equal to 4*MSS to avoid stop and go
 140  * tarrfic, not all TCP stacks do that.  This is especially true when
 141  * tcp_mss is a big value.
 142  *
 143  * To work around this issue, an additional fixed value for comparison
 144  * is also used.  If the advertised window is smaller than both tcp_mss
 145  * and tcp_init_wnd_chk, the ACK is considered as invalid.  So for large
 146  * tcp_mss value (say, 8K), a window larger than tcp_init_wnd_chk but
 147  * smaller than 8K is considered to be OK.
 148  */
 149 static uint32_t tcp_init_wnd_chk = 4096;
 150 
 151 /* Process ICMP source quench message or not. */
 152 static boolean_t tcp_icmp_source_quench = B_FALSE;
 153 
 154 static boolean_t tcp_outbound_squeue_switch = B_FALSE;
 155 
 156 static mblk_t   *tcp_conn_create_v4(conn_t *, conn_t *, mblk_t *,
 157                     ip_recv_attr_t *);
 158 static mblk_t   *tcp_conn_create_v6(conn_t *, conn_t *, mblk_t *,
 159                     ip_recv_attr_t *);
 160 static boolean_t        tcp_drop_q0(tcp_t *);
 161 static void     tcp_icmp_error_ipv6(tcp_t *, mblk_t *, ip_recv_attr_t *);
 162 static mblk_t   *tcp_input_add_ancillary(tcp_t *, mblk_t *, ip_pkt_t *,
 163                     ip_recv_attr_t *);
 164 static void     tcp_input_listener(void *, mblk_t *, void *, ip_recv_attr_t *);
 165 static void     tcp_process_options(tcp_t *, tcpha_t *);
 166 static mblk_t   *tcp_reass(tcp_t *, mblk_t *, uint32_t);
 167 static void     tcp_reass_elim_overlap(tcp_t *, mblk_t *);
 168 static void     tcp_rsrv_input(void *, mblk_t *, void *, ip_recv_attr_t *);
 169 static void     tcp_set_rto(tcp_t *, time_t);
 170 static void     tcp_setcred_data(mblk_t *, ip_recv_attr_t *);
 171 
 172 /*
 173  * Set the MSS associated with a particular tcp based on its current value,
 174  * and a new one passed in. Observe minimums and maximums, and reset other
 175  * state variables that we want to view as multiples of MSS.
 176  *
 177  * The value of MSS could be either increased or descreased.
 178  */
 179 void
 180 tcp_mss_set(tcp_t *tcp, uint32_t mss)
 181 {
 182         uint32_t        mss_max;
 183         tcp_stack_t     *tcps = tcp->tcp_tcps;
 184         conn_t          *connp = tcp->tcp_connp;
 185 
 186         if (connp->conn_ipversion == IPV4_VERSION)
 187                 mss_max = tcps->tcps_mss_max_ipv4;
 188         else
 189                 mss_max = tcps->tcps_mss_max_ipv6;
 190 
 191         if (mss < tcps->tcps_mss_min)
 192                 mss = tcps->tcps_mss_min;
 193         if (mss > mss_max)
 194                 mss = mss_max;
 195         /*
 196          * Unless naglim has been set by our client to
 197          * a non-mss value, force naglim to track mss.
 198          * This can help to aggregate small writes.
 199          */
 200         if (mss < tcp->tcp_naglim || tcp->tcp_mss == tcp->tcp_naglim)
 201                 tcp->tcp_naglim = mss;
 202         /*
 203          * TCP should be able to buffer at least 4 MSS data for obvious
 204          * performance reason.
 205          */
 206         if ((mss << 2) > connp->conn_sndbuf)
 207                 connp->conn_sndbuf = mss << 2;
 208 
 209         /*
 210          * Set the send lowater to at least twice of MSS.
 211          */
 212         if ((mss << 1) > connp->conn_sndlowat)
 213                 connp->conn_sndlowat = mss << 1;
 214 
 215         /*
 216          * Update tcp_cwnd according to the new value of MSS. Keep the
 217          * previous ratio to preserve the transmit rate.
 218          */
 219         tcp->tcp_cwnd = (tcp->tcp_cwnd / tcp->tcp_mss) * mss;
 220         tcp->tcp_cwnd_cnt = 0;
 221 
 222         tcp->tcp_mss = mss;
 223         (void) tcp_maxpsz_set(tcp, B_TRUE);
 224 }
 225 
 226 /*
 227  * Extract option values from a tcp header.  We put any found values into the
 228  * tcpopt struct and return a bitmask saying which options were found.
 229  */
 230 int
 231 tcp_parse_options(tcpha_t *tcpha, tcp_opt_t *tcpopt)
 232 {
 233         uchar_t         *endp;
 234         int             len;
 235         uint32_t        mss;
 236         uchar_t         *up = (uchar_t *)tcpha;
 237         int             found = 0;
 238         int32_t         sack_len;
 239         tcp_seq         sack_begin, sack_end;
 240         tcp_t           *tcp;
 241 
 242         endp = up + TCP_HDR_LENGTH(tcpha);
 243         up += TCP_MIN_HEADER_LENGTH;
 244         /*
 245          * If timestamp option is aligned as recommended in RFC 7323 Appendix
 246          * A, and is the only option, return quickly.
 247          */
 248         if (TCP_HDR_LENGTH(tcpha) == (uint32_t)TCP_MIN_HEADER_LENGTH +
 249             TCPOPT_REAL_TS_LEN &&
 250             OK_32PTR(up) &&
 251             *(uint32_t *)up == TCPOPT_NOP_NOP_TSTAMP) {
 252                 tcpopt->tcp_opt_ts_val = ABE32_TO_U32((up+4));
 253                 tcpopt->tcp_opt_ts_ecr = ABE32_TO_U32((up+8));
 254 
 255                 return (TCP_OPT_TSTAMP_PRESENT);
 256         }
 257         while (up < endp) {
 258                 len = endp - up;
 259                 switch (*up) {
 260                 case TCPOPT_EOL:
 261                         break;
 262 
 263                 case TCPOPT_NOP:
 264                         up++;
 265                         continue;
 266 
 267                 case TCPOPT_MAXSEG:
 268                         if (len < TCPOPT_MAXSEG_LEN ||
 269                             up[1] != TCPOPT_MAXSEG_LEN)
 270                                 break;
 271 
 272                         mss = BE16_TO_U16(up+2);
 273                         /* Caller must handle tcp_mss_min and tcp_mss_max_* */
 274                         tcpopt->tcp_opt_mss = mss;
 275                         found |= TCP_OPT_MSS_PRESENT;
 276 
 277                         up += TCPOPT_MAXSEG_LEN;
 278                         continue;
 279 
 280                 case TCPOPT_WSCALE:
 281                         if (len < TCPOPT_WS_LEN || up[1] != TCPOPT_WS_LEN)
 282                                 break;
 283 
 284                         if (up[2] > TCP_MAX_WINSHIFT)
 285                                 tcpopt->tcp_opt_wscale = TCP_MAX_WINSHIFT;
 286                         else
 287                                 tcpopt->tcp_opt_wscale = up[2];
 288                         found |= TCP_OPT_WSCALE_PRESENT;
 289 
 290                         up += TCPOPT_WS_LEN;
 291                         continue;
 292 
 293                 case TCPOPT_SACK_PERMITTED:
 294                         if (len < TCPOPT_SACK_OK_LEN ||
 295                             up[1] != TCPOPT_SACK_OK_LEN)
 296                                 break;
 297                         found |= TCP_OPT_SACK_OK_PRESENT;
 298                         up += TCPOPT_SACK_OK_LEN;
 299                         continue;
 300 
 301                 case TCPOPT_SACK:
 302                         if (len <= 2 || up[1] <= 2 || len < up[1])
 303                                 break;
 304 
 305                         /* If TCP is not interested in SACK blks... */
 306                         if ((tcp = tcpopt->tcp) == NULL) {
 307                                 up += up[1];
 308                                 continue;
 309                         }
 310                         sack_len = up[1] - TCPOPT_HEADER_LEN;
 311                         up += TCPOPT_HEADER_LEN;
 312 
 313                         /*
 314                          * If the list is empty, allocate one and assume
 315                          * nothing is sack'ed.
 316                          */
 317                         if (tcp->tcp_notsack_list == NULL) {
 318                                 tcp_notsack_update(&(tcp->tcp_notsack_list),
 319                                     tcp->tcp_suna, tcp->tcp_snxt,
 320                                     &(tcp->tcp_num_notsack_blk),
 321                                     &(tcp->tcp_cnt_notsack_list));
 322 
 323                                 /*
 324                                  * Make sure tcp_notsack_list is not NULL.
 325                                  * This happens when kmem_alloc(KM_NOSLEEP)
 326                                  * returns NULL.
 327                                  */
 328                                 if (tcp->tcp_notsack_list == NULL) {
 329                                         up += sack_len;
 330                                         continue;
 331                                 }
 332                                 tcp->tcp_fack = tcp->tcp_suna;
 333                         }
 334 
 335                         while (sack_len > 0) {
 336                                 if (up + 8 > endp) {
 337                                         up = endp;
 338                                         break;
 339                                 }
 340                                 sack_begin = BE32_TO_U32(up);
 341                                 up += 4;
 342                                 sack_end = BE32_TO_U32(up);
 343                                 up += 4;
 344                                 sack_len -= 8;
 345                                 /*
 346                                  * Bounds checking.  Make sure the SACK
 347                                  * info is within tcp_suna and tcp_snxt.
 348                                  * If this SACK blk is out of bound, ignore
 349                                  * it but continue to parse the following
 350                                  * blks.
 351                                  */
 352                                 if (SEQ_LEQ(sack_end, sack_begin) ||
 353                                     SEQ_LT(sack_begin, tcp->tcp_suna) ||
 354                                     SEQ_GT(sack_end, tcp->tcp_snxt)) {
 355                                         continue;
 356                                 }
 357                                 tcp_notsack_insert(&(tcp->tcp_notsack_list),
 358                                     sack_begin, sack_end,
 359                                     &(tcp->tcp_num_notsack_blk),
 360                                     &(tcp->tcp_cnt_notsack_list));
 361                                 if (SEQ_GT(sack_end, tcp->tcp_fack)) {
 362                                         tcp->tcp_fack = sack_end;
 363                                 }
 364                         }
 365                         found |= TCP_OPT_SACK_PRESENT;
 366                         continue;
 367 
 368                 case TCPOPT_TSTAMP:
 369                         if (len < TCPOPT_TSTAMP_LEN ||
 370                             up[1] != TCPOPT_TSTAMP_LEN)
 371                                 break;
 372 
 373                         tcpopt->tcp_opt_ts_val = BE32_TO_U32(up+2);
 374                         tcpopt->tcp_opt_ts_ecr = BE32_TO_U32(up+6);
 375 
 376                         found |= TCP_OPT_TSTAMP_PRESENT;
 377 
 378                         up += TCPOPT_TSTAMP_LEN;
 379                         continue;
 380 
 381                 default:
 382                         if (len <= 1 || len < (int)up[1] || up[1] == 0)
 383                                 break;
 384                         up += up[1];
 385                         continue;
 386                 }
 387                 break;
 388         }
 389         return (found);
 390 }
 391 
 392 /*
 393  * Process all TCP option in SYN segment.  Note that this function should
 394  * be called after tcp_set_destination() is called so that the necessary info
 395  * from IRE is already set in the tcp structure.
 396  *
 397  * This function sets up the correct tcp_mss value according to the
 398  * MSS option value and our header size.  It also sets up the window scale
 399  * and timestamp values, and initialize SACK info blocks.  But it does not
 400  * change receive window size after setting the tcp_mss value.  The caller
 401  * should do the appropriate change.
 402  */
 403 static void
 404 tcp_process_options(tcp_t *tcp, tcpha_t *tcpha)
 405 {
 406         int options;
 407         tcp_opt_t tcpopt;
 408         uint32_t mss_max;
 409         char *tmp_tcph;
 410         tcp_stack_t     *tcps = tcp->tcp_tcps;
 411         conn_t          *connp = tcp->tcp_connp;
 412 
 413         tcpopt.tcp = NULL;
 414         options = tcp_parse_options(tcpha, &tcpopt);
 415 
 416         /*
 417          * Process MSS option.  Note that MSS option value does not account
 418          * for IP or TCP options.  This means that it is equal to MTU - minimum
 419          * IP+TCP header size, which is 40 bytes for IPv4 and 60 bytes for
 420          * IPv6.
 421          */
 422         if (!(options & TCP_OPT_MSS_PRESENT)) {
 423                 if (connp->conn_ipversion == IPV4_VERSION)
 424                         tcpopt.tcp_opt_mss = tcps->tcps_mss_def_ipv4;
 425                 else
 426                         tcpopt.tcp_opt_mss = tcps->tcps_mss_def_ipv6;
 427         } else {
 428                 if (connp->conn_ipversion == IPV4_VERSION)
 429                         mss_max = tcps->tcps_mss_max_ipv4;
 430                 else
 431                         mss_max = tcps->tcps_mss_max_ipv6;
 432                 if (tcpopt.tcp_opt_mss < tcps->tcps_mss_min)
 433                         tcpopt.tcp_opt_mss = tcps->tcps_mss_min;
 434                 else if (tcpopt.tcp_opt_mss > mss_max)
 435                         tcpopt.tcp_opt_mss = mss_max;
 436         }
 437 
 438         /* Process Window Scale option. */
 439         if (options & TCP_OPT_WSCALE_PRESENT) {
 440                 tcp->tcp_snd_ws = tcpopt.tcp_opt_wscale;
 441                 tcp->tcp_snd_ws_ok = B_TRUE;
 442         } else {
 443                 tcp->tcp_snd_ws = B_FALSE;
 444                 tcp->tcp_snd_ws_ok = B_FALSE;
 445                 tcp->tcp_rcv_ws = B_FALSE;
 446         }
 447 
 448         /* Process Timestamp option. */
 449         if ((options & TCP_OPT_TSTAMP_PRESENT) &&
 450             (tcp->tcp_snd_ts_ok || TCP_IS_DETACHED(tcp))) {
 451                 tmp_tcph = (char *)tcp->tcp_tcpha;
 452 
 453                 tcp->tcp_snd_ts_ok = B_TRUE;
 454                 tcp->tcp_ts_recent = tcpopt.tcp_opt_ts_val;
 455                 tcp->tcp_last_rcv_lbolt = ddi_get_lbolt64();
 456                 ASSERT(OK_32PTR(tmp_tcph));
 457                 ASSERT(connp->conn_ht_ulp_len == TCP_MIN_HEADER_LENGTH);
 458 
 459                 /* Fill in our template header with basic timestamp option. */
 460                 tmp_tcph += connp->conn_ht_ulp_len;
 461                 tmp_tcph[0] = TCPOPT_NOP;
 462                 tmp_tcph[1] = TCPOPT_NOP;
 463                 tmp_tcph[2] = TCPOPT_TSTAMP;
 464                 tmp_tcph[3] = TCPOPT_TSTAMP_LEN;
 465                 connp->conn_ht_iphc_len += TCPOPT_REAL_TS_LEN;
 466                 connp->conn_ht_ulp_len += TCPOPT_REAL_TS_LEN;
 467                 tcp->tcp_tcpha->tha_offset_and_reserved += (3 << 4);
 468         } else {
 469                 tcp->tcp_snd_ts_ok = B_FALSE;
 470         }
 471 
 472         /*
 473          * Process SACK options.  If SACK is enabled for this connection,
 474          * then allocate the SACK info structure.  Note the following ways
 475          * when tcp_snd_sack_ok is set to true.
 476          *
 477          * For active connection: in tcp_set_destination() called in
 478          * tcp_connect().
 479          *
 480          * For passive connection: in tcp_set_destination() called in
 481          * tcp_input_listener().
 482          *
 483          * That's the reason why the extra TCP_IS_DETACHED() check is there.
 484          * That check makes sure that if we did not send a SACK OK option,
 485          * we will not enable SACK for this connection even though the other
 486          * side sends us SACK OK option.  For active connection, the SACK
 487          * info structure has already been allocated.  So we need to free
 488          * it if SACK is disabled.
 489          */
 490         if ((options & TCP_OPT_SACK_OK_PRESENT) &&
 491             (tcp->tcp_snd_sack_ok ||
 492             (tcps->tcps_sack_permitted != 0 && TCP_IS_DETACHED(tcp)))) {
 493                 ASSERT(tcp->tcp_num_sack_blk == 0);
 494                 ASSERT(tcp->tcp_notsack_list == NULL);
 495 
 496                 tcp->tcp_snd_sack_ok = B_TRUE;
 497                 if (tcp->tcp_snd_ts_ok) {
 498                         tcp->tcp_max_sack_blk = 3;
 499                 } else {
 500                         tcp->tcp_max_sack_blk = 4;
 501                 }
 502         } else if (tcp->tcp_snd_sack_ok) {
 503                 /*
 504                  * Resetting tcp_snd_sack_ok to B_FALSE so that
 505                  * no SACK info will be used for this
 506                  * connection.  This assumes that SACK usage
 507                  * permission is negotiated.  This may need
 508                  * to be changed once this is clarified.
 509                  */
 510                 ASSERT(tcp->tcp_num_sack_blk == 0);
 511                 ASSERT(tcp->tcp_notsack_list == NULL);
 512                 tcp->tcp_snd_sack_ok = B_FALSE;
 513         }
 514 
 515         /*
 516          * Now we know the exact TCP/IP header length, subtract
 517          * that from tcp_mss to get our side's MSS.
 518          */
 519         tcp->tcp_mss -= connp->conn_ht_iphc_len;
 520 
 521         /*
 522          * Here we assume that the other side's header size will be equal to
 523          * our header size.  We calculate the real MSS accordingly.  Need to
 524          * take into additional stuffs IPsec puts in.
 525          *
 526          * Real MSS = Opt.MSS - (our TCP/IP header - min TCP/IP header)
 527          */
 528         tcpopt.tcp_opt_mss -= connp->conn_ht_iphc_len +
 529             tcp->tcp_ipsec_overhead -
 530             ((connp->conn_ipversion == IPV4_VERSION ?
 531             IP_SIMPLE_HDR_LENGTH : IPV6_HDR_LEN) + TCP_MIN_HEADER_LENGTH);
 532 
 533         /*
 534          * Set MSS to the smaller one of both ends of the connection.
 535          * We should not have called tcp_mss_set() before, but our
 536          * side of the MSS should have been set to a proper value
 537          * by tcp_set_destination().  tcp_mss_set() will also set up the
 538          * STREAM head parameters properly.
 539          *
 540          * If we have a larger-than-16-bit window but the other side
 541          * didn't want to do window scale, tcp_rwnd_set() will take
 542          * care of that.
 543          */
 544         tcp_mss_set(tcp, MIN(tcpopt.tcp_opt_mss, tcp->tcp_mss));
 545 
 546         /*
 547          * Initialize tcp_cwnd value. After tcp_mss_set(), tcp_mss has been
 548          * updated properly.
 549          */
 550         TCP_SET_INIT_CWND(tcp, tcp->tcp_mss, tcps->tcps_slow_start_initial);
 551 }
 552 
 553 /*
 554  * Add a new piece to the tcp reassembly queue.  If the gap at the beginning
 555  * is filled, return as much as we can.  The message passed in may be
 556  * multi-part, chained using b_cont.  "start" is the starting sequence
 557  * number for this piece.
 558  */
 559 static mblk_t *
 560 tcp_reass(tcp_t *tcp, mblk_t *mp, uint32_t start)
 561 {
 562         uint32_t        end;
 563         mblk_t          *mp1;
 564         mblk_t          *mp2;
 565         mblk_t          *next_mp;
 566         uint32_t        u1;
 567         tcp_stack_t     *tcps = tcp->tcp_tcps;
 568 
 569 
 570         /* Walk through all the new pieces. */
 571         do {
 572                 ASSERT((uintptr_t)(mp->b_wptr - mp->b_rptr) <=
 573                     (uintptr_t)INT_MAX);
 574                 end = start + (int)(mp->b_wptr - mp->b_rptr);
 575                 next_mp = mp->b_cont;
 576                 if (start == end) {
 577                         /* Empty.  Blast it. */
 578                         freeb(mp);
 579                         continue;
 580                 }
 581                 mp->b_cont = NULL;
 582                 TCP_REASS_SET_SEQ(mp, start);
 583                 TCP_REASS_SET_END(mp, end);
 584                 mp1 = tcp->tcp_reass_tail;
 585                 if (!mp1) {
 586                         tcp->tcp_reass_tail = mp;
 587                         tcp->tcp_reass_head = mp;
 588                         TCPS_BUMP_MIB(tcps, tcpInDataUnorderSegs);
 589                         TCPS_UPDATE_MIB(tcps, tcpInDataUnorderBytes,
 590                             end - start);
 591                         continue;
 592                 }
 593                 /* New stuff completely beyond tail? */
 594                 if (SEQ_GEQ(start, TCP_REASS_END(mp1))) {
 595                         /* Link it on end. */
 596                         mp1->b_cont = mp;
 597                         tcp->tcp_reass_tail = mp;
 598                         TCPS_BUMP_MIB(tcps, tcpInDataUnorderSegs);
 599                         TCPS_UPDATE_MIB(tcps, tcpInDataUnorderBytes,
 600                             end - start);
 601                         continue;
 602                 }
 603                 mp1 = tcp->tcp_reass_head;
 604                 u1 = TCP_REASS_SEQ(mp1);
 605                 /* New stuff at the front? */
 606                 if (SEQ_LT(start, u1)) {
 607                         /* Yes... Check for overlap. */
 608                         mp->b_cont = mp1;
 609                         tcp->tcp_reass_head = mp;
 610                         tcp_reass_elim_overlap(tcp, mp);
 611                         continue;
 612                 }
 613                 /*
 614                  * The new piece fits somewhere between the head and tail.
 615                  * We find our slot, where mp1 precedes us and mp2 trails.
 616                  */
 617                 for (; (mp2 = mp1->b_cont) != NULL; mp1 = mp2) {
 618                         u1 = TCP_REASS_SEQ(mp2);
 619                         if (SEQ_LEQ(start, u1))
 620                                 break;
 621                 }
 622                 /* Link ourselves in */
 623                 mp->b_cont = mp2;
 624                 mp1->b_cont = mp;
 625 
 626                 /* Trim overlap with following mblk(s) first */
 627                 tcp_reass_elim_overlap(tcp, mp);
 628 
 629                 /* Trim overlap with preceding mblk */
 630                 tcp_reass_elim_overlap(tcp, mp1);
 631 
 632         } while (start = end, mp = next_mp);
 633         mp1 = tcp->tcp_reass_head;
 634         /* Anything ready to go? */
 635         if (TCP_REASS_SEQ(mp1) != tcp->tcp_rnxt)
 636                 return (NULL);
 637         /* Eat what we can off the queue */
 638         for (;;) {
 639                 mp = mp1->b_cont;
 640                 end = TCP_REASS_END(mp1);
 641                 TCP_REASS_SET_SEQ(mp1, 0);
 642                 TCP_REASS_SET_END(mp1, 0);
 643                 if (!mp) {
 644                         tcp->tcp_reass_tail = NULL;
 645                         break;
 646                 }
 647                 if (end != TCP_REASS_SEQ(mp)) {
 648                         mp1->b_cont = NULL;
 649                         break;
 650                 }
 651                 mp1 = mp;
 652         }
 653         mp1 = tcp->tcp_reass_head;
 654         tcp->tcp_reass_head = mp;
 655         return (mp1);
 656 }
 657 
 658 /* Eliminate any overlap that mp may have over later mblks */
 659 static void
 660 tcp_reass_elim_overlap(tcp_t *tcp, mblk_t *mp)
 661 {
 662         uint32_t        end;
 663         mblk_t          *mp1;
 664         uint32_t        u1;
 665         tcp_stack_t     *tcps = tcp->tcp_tcps;
 666 
 667         end = TCP_REASS_END(mp);
 668         while ((mp1 = mp->b_cont) != NULL) {
 669                 u1 = TCP_REASS_SEQ(mp1);
 670                 if (!SEQ_GT(end, u1))
 671                         break;
 672                 if (!SEQ_GEQ(end, TCP_REASS_END(mp1))) {
 673                         mp->b_wptr -= end - u1;
 674                         TCP_REASS_SET_END(mp, u1);
 675                         TCPS_BUMP_MIB(tcps, tcpInDataPartDupSegs);
 676                         TCPS_UPDATE_MIB(tcps, tcpInDataPartDupBytes,
 677                             end - u1);
 678                         break;
 679                 }
 680                 mp->b_cont = mp1->b_cont;
 681                 TCP_REASS_SET_SEQ(mp1, 0);
 682                 TCP_REASS_SET_END(mp1, 0);
 683                 freeb(mp1);
 684                 TCPS_BUMP_MIB(tcps, tcpInDataDupSegs);
 685                 TCPS_UPDATE_MIB(tcps, tcpInDataDupBytes, end - u1);
 686         }
 687         if (!mp1)
 688                 tcp->tcp_reass_tail = mp;
 689 }
 690 
 691 /*
 692  * This function does PAWS protection check, per RFC 7323 section 5. Requires
 693  * that timestamp options are already processed into tcpoptp. Returns B_TRUE if
 694  * the segment passes the PAWS test, else returns B_FALSE.
 695  */
 696 boolean_t
 697 tcp_paws_check(tcp_t *tcp, const tcp_opt_t *tcpoptp)
 698 {
 699         if (TSTMP_LT(tcpoptp->tcp_opt_ts_val,
 700             tcp->tcp_ts_recent)) {
 701                 if (LBOLT_FASTPATH64 <
 702                     (tcp->tcp_last_rcv_lbolt + PAWS_TIMEOUT)) {
 703                         /* This segment is not acceptable. */
 704                         return (B_FALSE);
 705                 } else {
 706                         /*
 707                          * Connection has been idle for
 708                          * too long.  Reset the timestamp
 709                          */
 710                         tcp->tcp_ts_recent =
 711                             tcpoptp->tcp_opt_ts_val;
 712                 }
 713         }
 714         return (B_TRUE);
 715 }
 716 
 717 /*
 718  * Defense for the SYN attack -
 719  * 1. When q0 is full, drop from the tail (tcp_eager_prev_drop_q0) the oldest
 720  *    one from the list of droppable eagers. This list is a subset of q0.
 721  *    see comments before the definition of MAKE_DROPPABLE().
 722  * 2. Don't drop a SYN request before its first timeout. This gives every
 723  *    request at least til the first timeout to complete its 3-way handshake.
 724  * 3. Maintain tcp_syn_rcvd_timeout as an accurate count of how many
 725  *    requests currently on the queue that has timed out. This will be used
 726  *    as an indicator of whether an attack is under way, so that appropriate
 727  *    actions can be taken. (It's incremented in tcp_timer() and decremented
 728  *    either when eager goes into ESTABLISHED, or gets freed up.)
 729  * 4. The current threshold is - # of timeout > q0len/4 => SYN alert on
 730  *    # of timeout drops back to <= q0len/32 => SYN alert off
 731  */
 732 static boolean_t
 733 tcp_drop_q0(tcp_t *tcp)
 734 {
 735         tcp_t   *eager;
 736         mblk_t  *mp;
 737         tcp_stack_t     *tcps = tcp->tcp_tcps;
 738 
 739         ASSERT(MUTEX_HELD(&tcp->tcp_eager_lock));
 740         ASSERT(tcp->tcp_eager_next_q0 != tcp->tcp_eager_prev_q0);
 741 
 742         /* Pick oldest eager from the list of droppable eagers */
 743         eager = tcp->tcp_eager_prev_drop_q0;
 744 
 745         /* If list is empty. return B_FALSE */
 746         if (eager == tcp) {
 747                 return (B_FALSE);
 748         }
 749 
 750         /* If allocated, the mp will be freed in tcp_clean_death_wrapper() */
 751         if ((mp = allocb(0, BPRI_HI)) == NULL)
 752                 return (B_FALSE);
 753 
 754         /*
 755          * Take this eager out from the list of droppable eagers since we are
 756          * going to drop it.
 757          */
 758         MAKE_UNDROPPABLE(eager);
 759 
 760         if (tcp->tcp_connp->conn_debug) {
 761                 (void) strlog(TCP_MOD_ID, 0, 3, SL_TRACE,
 762                     "tcp_drop_q0: listen half-open queue (max=%d) overflow"
 763                     " (%d pending) on %s, drop one", tcps->tcps_conn_req_max_q0,
 764                     tcp->tcp_conn_req_cnt_q0,
 765                     tcp_display(tcp, NULL, DISP_PORT_ONLY));
 766         }
 767 
 768         TCPS_BUMP_MIB(tcps, tcpHalfOpenDrop);
 769 
 770         /* Put a reference on the conn as we are enqueueing it in the sqeue */
 771         CONN_INC_REF(eager->tcp_connp);
 772 
 773         SQUEUE_ENTER_ONE(eager->tcp_connp->conn_sqp, mp,
 774             tcp_clean_death_wrapper, eager->tcp_connp, NULL,
 775             SQ_FILL, SQTAG_TCP_DROP_Q0);
 776 
 777         return (B_TRUE);
 778 }
 779 
 780 /*
 781  * Handle a SYN on an AF_INET6 socket; can be either IPv4 or IPv6
 782  */
 783 static mblk_t *
 784 tcp_conn_create_v6(conn_t *lconnp, conn_t *connp, mblk_t *mp,
 785     ip_recv_attr_t *ira)
 786 {
 787         tcp_t           *ltcp = lconnp->conn_tcp;
 788         tcp_t           *tcp = connp->conn_tcp;
 789         mblk_t          *tpi_mp;
 790         ipha_t          *ipha;
 791         ip6_t           *ip6h;
 792         sin6_t          sin6;
 793         uint_t          ifindex = ira->ira_ruifindex;
 794         tcp_stack_t     *tcps = tcp->tcp_tcps;
 795 
 796         if (ira->ira_flags & IRAF_IS_IPV4) {
 797                 ipha = (ipha_t *)mp->b_rptr;
 798 
 799                 connp->conn_ipversion = IPV4_VERSION;
 800                 IN6_IPADDR_TO_V4MAPPED(ipha->ipha_dst, &connp->conn_laddr_v6);
 801                 IN6_IPADDR_TO_V4MAPPED(ipha->ipha_src, &connp->conn_faddr_v6);
 802                 connp->conn_saddr_v6 = connp->conn_laddr_v6;
 803 
 804                 sin6 = sin6_null;
 805                 sin6.sin6_addr = connp->conn_faddr_v6;
 806                 sin6.sin6_port = connp->conn_fport;
 807                 sin6.sin6_family = AF_INET6;
 808                 sin6.__sin6_src_id = ip_srcid_find_addr(&connp->conn_laddr_v6,
 809                     IPCL_ZONEID(lconnp), tcps->tcps_netstack);
 810 
 811                 if (connp->conn_recv_ancillary.crb_recvdstaddr) {
 812                         sin6_t  sin6d;
 813 
 814                         sin6d = sin6_null;
 815                         sin6d.sin6_addr = connp->conn_laddr_v6;
 816                         sin6d.sin6_port = connp->conn_lport;
 817                         sin6d.sin6_family = AF_INET;
 818                         tpi_mp = mi_tpi_extconn_ind(NULL,
 819                             (char *)&sin6d, sizeof (sin6_t),
 820                             (char *)&tcp,
 821                             (t_scalar_t)sizeof (intptr_t),
 822                             (char *)&sin6d, sizeof (sin6_t),
 823                             (t_scalar_t)ltcp->tcp_conn_req_seqnum);
 824                 } else {
 825                         tpi_mp = mi_tpi_conn_ind(NULL,
 826                             (char *)&sin6, sizeof (sin6_t),
 827                             (char *)&tcp, (t_scalar_t)sizeof (intptr_t),
 828                             (t_scalar_t)ltcp->tcp_conn_req_seqnum);
 829                 }
 830         } else {
 831                 ip6h = (ip6_t *)mp->b_rptr;
 832 
 833                 connp->conn_ipversion = IPV6_VERSION;
 834                 connp->conn_laddr_v6 = ip6h->ip6_dst;
 835                 connp->conn_faddr_v6 = ip6h->ip6_src;
 836                 connp->conn_saddr_v6 = connp->conn_laddr_v6;
 837 
 838                 sin6 = sin6_null;
 839                 sin6.sin6_addr = connp->conn_faddr_v6;
 840                 sin6.sin6_port = connp->conn_fport;
 841                 sin6.sin6_family = AF_INET6;
 842                 sin6.sin6_flowinfo = ip6h->ip6_vcf & ~IPV6_VERS_AND_FLOW_MASK;
 843                 sin6.__sin6_src_id = ip_srcid_find_addr(&connp->conn_laddr_v6,
 844                     IPCL_ZONEID(lconnp), tcps->tcps_netstack);
 845 
 846                 if (IN6_IS_ADDR_LINKSCOPE(&ip6h->ip6_src)) {
 847                         /* Pass up the scope_id of remote addr */
 848                         sin6.sin6_scope_id = ifindex;
 849                 } else {
 850                         sin6.sin6_scope_id = 0;
 851                 }
 852                 if (connp->conn_recv_ancillary.crb_recvdstaddr) {
 853                         sin6_t  sin6d;
 854 
 855                         sin6d = sin6_null;
 856                         sin6.sin6_addr = connp->conn_laddr_v6;
 857                         sin6d.sin6_port = connp->conn_lport;
 858                         sin6d.sin6_family = AF_INET6;
 859                         if (IN6_IS_ADDR_LINKSCOPE(&connp->conn_laddr_v6))
 860                                 sin6d.sin6_scope_id = ifindex;
 861 
 862                         tpi_mp = mi_tpi_extconn_ind(NULL,
 863                             (char *)&sin6d, sizeof (sin6_t),
 864                             (char *)&tcp, (t_scalar_t)sizeof (intptr_t),
 865                             (char *)&sin6d, sizeof (sin6_t),
 866                             (t_scalar_t)ltcp->tcp_conn_req_seqnum);
 867                 } else {
 868                         tpi_mp = mi_tpi_conn_ind(NULL,
 869                             (char *)&sin6, sizeof (sin6_t),
 870                             (char *)&tcp, (t_scalar_t)sizeof (intptr_t),
 871                             (t_scalar_t)ltcp->tcp_conn_req_seqnum);
 872                 }
 873         }
 874 
 875         tcp->tcp_mss = tcps->tcps_mss_def_ipv6;
 876         return (tpi_mp);
 877 }
 878 
 879 /* Handle a SYN on an AF_INET socket */
 880 static mblk_t *
 881 tcp_conn_create_v4(conn_t *lconnp, conn_t *connp, mblk_t *mp,
 882     ip_recv_attr_t *ira)
 883 {
 884         tcp_t           *ltcp = lconnp->conn_tcp;
 885         tcp_t           *tcp = connp->conn_tcp;
 886         sin_t           sin;
 887         mblk_t          *tpi_mp = NULL;
 888         tcp_stack_t     *tcps = tcp->tcp_tcps;
 889         ipha_t          *ipha;
 890 
 891         ASSERT(ira->ira_flags & IRAF_IS_IPV4);
 892         ipha = (ipha_t *)mp->b_rptr;
 893 
 894         connp->conn_ipversion = IPV4_VERSION;
 895         IN6_IPADDR_TO_V4MAPPED(ipha->ipha_dst, &connp->conn_laddr_v6);
 896         IN6_IPADDR_TO_V4MAPPED(ipha->ipha_src, &connp->conn_faddr_v6);
 897         connp->conn_saddr_v6 = connp->conn_laddr_v6;
 898 
 899         sin = sin_null;
 900         sin.sin_addr.s_addr = connp->conn_faddr_v4;
 901         sin.sin_port = connp->conn_fport;
 902         sin.sin_family = AF_INET;
 903         if (lconnp->conn_recv_ancillary.crb_recvdstaddr) {
 904                 sin_t   sind;
 905 
 906                 sind = sin_null;
 907                 sind.sin_addr.s_addr = connp->conn_laddr_v4;
 908                 sind.sin_port = connp->conn_lport;
 909                 sind.sin_family = AF_INET;
 910                 tpi_mp = mi_tpi_extconn_ind(NULL,
 911                     (char *)&sind, sizeof (sin_t), (char *)&tcp,
 912                     (t_scalar_t)sizeof (intptr_t), (char *)&sind,
 913                     sizeof (sin_t), (t_scalar_t)ltcp->tcp_conn_req_seqnum);
 914         } else {
 915                 tpi_mp = mi_tpi_conn_ind(NULL,
 916                     (char *)&sin, sizeof (sin_t),
 917                     (char *)&tcp, (t_scalar_t)sizeof (intptr_t),
 918                     (t_scalar_t)ltcp->tcp_conn_req_seqnum);
 919         }
 920 
 921         tcp->tcp_mss = tcps->tcps_mss_def_ipv4;
 922         return (tpi_mp);
 923 }
 924 
 925 /*
 926  * Called via squeue to get on to eager's perimeter. It sends a
 927  * TH_RST if eager is in the fanout table. The listener wants the
 928  * eager to disappear either by means of tcp_eager_blowoff() or
 929  * tcp_eager_cleanup() being called. tcp_eager_kill() can also be
 930  * called (via squeue) if the eager cannot be inserted in the
 931  * fanout table in tcp_input_listener().
 932  */
 933 /* ARGSUSED */
 934 void
 935 tcp_eager_kill(void *arg, mblk_t *mp, void *arg2, ip_recv_attr_t *dummy)
 936 {
 937         conn_t  *econnp = (conn_t *)arg;
 938         tcp_t   *eager = econnp->conn_tcp;
 939         tcp_t   *listener = eager->tcp_listener;
 940 
 941         /*
 942          * We could be called because listener is closing. Since
 943          * the eager was using listener's queue's, we avoid
 944          * using the listeners queues from now on.
 945          */
 946         ASSERT(eager->tcp_detached);
 947         econnp->conn_rq = NULL;
 948         econnp->conn_wq = NULL;
 949 
 950         /*
 951          * An eager's conn_fanout will be NULL if it's a duplicate
 952          * for an existing 4-tuples in the conn fanout table.
 953          * We don't want to send an RST out in such case.
 954          */
 955         if (econnp->conn_fanout != NULL && eager->tcp_state > TCPS_LISTEN) {
 956                 tcp_xmit_ctl("tcp_eager_kill, can't wait",
 957                     eager, eager->tcp_snxt, 0, TH_RST);
 958         }
 959 
 960         /* We are here because listener wants this eager gone */
 961         if (listener != NULL) {
 962                 mutex_enter(&listener->tcp_eager_lock);
 963                 tcp_eager_unlink(eager);
 964                 if (eager->tcp_tconnind_started) {
 965                         /*
 966                          * The eager has sent a conn_ind up to the
 967                          * listener but listener decides to close
 968                          * instead. We need to drop the extra ref
 969                          * placed on eager in tcp_input_data() before
 970                          * sending the conn_ind to listener.
 971                          */
 972                         CONN_DEC_REF(econnp);
 973                 }
 974                 mutex_exit(&listener->tcp_eager_lock);
 975                 CONN_DEC_REF(listener->tcp_connp);
 976         }
 977 
 978         if (eager->tcp_state != TCPS_CLOSED)
 979                 tcp_close_detached(eager);
 980 }
 981 
 982 /*
 983  * Reset any eager connection hanging off this listener marked
 984  * with 'seqnum' and then reclaim it's resources.
 985  */
 986 boolean_t
 987 tcp_eager_blowoff(tcp_t *listener, t_scalar_t seqnum)
 988 {
 989         tcp_t   *eager;
 990         mblk_t  *mp;
 991 
 992         eager = listener;
 993         mutex_enter(&listener->tcp_eager_lock);
 994         do {
 995                 eager = eager->tcp_eager_next_q;
 996                 if (eager == NULL) {
 997                         mutex_exit(&listener->tcp_eager_lock);
 998                         return (B_FALSE);
 999                 }
1000         } while (eager->tcp_conn_req_seqnum != seqnum);
1001 
1002         if (eager->tcp_closemp_used) {
1003                 mutex_exit(&listener->tcp_eager_lock);
1004                 return (B_TRUE);
1005         }
1006         eager->tcp_closemp_used = B_TRUE;
1007         TCP_DEBUG_GETPCSTACK(eager->tcmp_stk, 15);
1008         CONN_INC_REF(eager->tcp_connp);
1009         mutex_exit(&listener->tcp_eager_lock);
1010         mp = &eager->tcp_closemp;
1011         SQUEUE_ENTER_ONE(eager->tcp_connp->conn_sqp, mp, tcp_eager_kill,
1012             eager->tcp_connp, NULL, SQ_FILL, SQTAG_TCP_EAGER_BLOWOFF);
1013         return (B_TRUE);
1014 }
1015 
1016 /*
1017  * Reset any eager connection hanging off this listener
1018  * and then reclaim it's resources.
1019  */
1020 void
1021 tcp_eager_cleanup(tcp_t *listener, boolean_t q0_only)
1022 {
1023         tcp_t   *eager;
1024         mblk_t  *mp;
1025         tcp_stack_t     *tcps = listener->tcp_tcps;
1026 
1027         ASSERT(MUTEX_HELD(&listener->tcp_eager_lock));
1028 
1029         if (!q0_only) {
1030                 /* First cleanup q */
1031                 TCP_STAT(tcps, tcp_eager_blowoff_q);
1032                 eager = listener->tcp_eager_next_q;
1033                 while (eager != NULL) {
1034                         if (!eager->tcp_closemp_used) {
1035                                 eager->tcp_closemp_used = B_TRUE;
1036                                 TCP_DEBUG_GETPCSTACK(eager->tcmp_stk, 15);
1037                                 CONN_INC_REF(eager->tcp_connp);
1038                                 mp = &eager->tcp_closemp;
1039                                 SQUEUE_ENTER_ONE(eager->tcp_connp->conn_sqp, mp,
1040                                     tcp_eager_kill, eager->tcp_connp, NULL,
1041                                     SQ_FILL, SQTAG_TCP_EAGER_CLEANUP);
1042                         }
1043                         eager = eager->tcp_eager_next_q;
1044                 }
1045         }
1046         /* Then cleanup q0 */
1047         TCP_STAT(tcps, tcp_eager_blowoff_q0);
1048         eager = listener->tcp_eager_next_q0;
1049         while (eager != listener) {
1050                 if (!eager->tcp_closemp_used) {
1051                         eager->tcp_closemp_used = B_TRUE;
1052                         TCP_DEBUG_GETPCSTACK(eager->tcmp_stk, 15);
1053                         CONN_INC_REF(eager->tcp_connp);
1054                         mp = &eager->tcp_closemp;
1055                         SQUEUE_ENTER_ONE(eager->tcp_connp->conn_sqp, mp,
1056                             tcp_eager_kill, eager->tcp_connp, NULL, SQ_FILL,
1057                             SQTAG_TCP_EAGER_CLEANUP_Q0);
1058                 }
1059                 eager = eager->tcp_eager_next_q0;
1060         }
1061 }
1062 
1063 /*
1064  * If we are an eager connection hanging off a listener that hasn't
1065  * formally accepted the connection yet, get off its list and blow off
1066  * any data that we have accumulated.
1067  */
1068 void
1069 tcp_eager_unlink(tcp_t *tcp)
1070 {
1071         tcp_t   *listener = tcp->tcp_listener;
1072 
1073         ASSERT(listener != NULL);
1074         ASSERT(MUTEX_HELD(&listener->tcp_eager_lock));
1075         if (tcp->tcp_eager_next_q0 != NULL) {
1076                 ASSERT(tcp->tcp_eager_prev_q0 != NULL);
1077 
1078                 /* Remove the eager tcp from q0 */
1079                 tcp->tcp_eager_next_q0->tcp_eager_prev_q0 =
1080                     tcp->tcp_eager_prev_q0;
1081                 tcp->tcp_eager_prev_q0->tcp_eager_next_q0 =
1082                     tcp->tcp_eager_next_q0;
1083                 ASSERT(listener->tcp_conn_req_cnt_q0 > 0);
1084                 listener->tcp_conn_req_cnt_q0--;
1085 
1086                 tcp->tcp_eager_next_q0 = NULL;
1087                 tcp->tcp_eager_prev_q0 = NULL;
1088 
1089                 /*
1090                  * Take the eager out, if it is in the list of droppable
1091                  * eagers.
1092                  */
1093                 MAKE_UNDROPPABLE(tcp);
1094 
1095                 if (tcp->tcp_syn_rcvd_timeout != 0) {
1096                         /* we have timed out before */
1097                         ASSERT(listener->tcp_syn_rcvd_timeout > 0);
1098                         listener->tcp_syn_rcvd_timeout--;
1099                 }
1100         } else {
1101                 tcp_t   **tcpp = &listener->tcp_eager_next_q;
1102                 tcp_t   *prev = NULL;
1103 
1104                 for (; tcpp[0]; tcpp = &tcpp[0]->tcp_eager_next_q) {
1105                         if (tcpp[0] == tcp) {
1106                                 if (listener->tcp_eager_last_q == tcp) {
1107                                         /*
1108                                          * If we are unlinking the last
1109                                          * element on the list, adjust
1110                                          * tail pointer. Set tail pointer
1111                                          * to nil when list is empty.
1112                                          */
1113                                         ASSERT(tcp->tcp_eager_next_q == NULL);
1114                                         if (listener->tcp_eager_last_q ==
1115                                             listener->tcp_eager_next_q) {
1116                                                 listener->tcp_eager_last_q =
1117                                                     NULL;
1118                                         } else {
1119                                                 /*
1120                                                  * We won't get here if there
1121                                                  * is only one eager in the
1122                                                  * list.
1123                                                  */
1124                                                 ASSERT(prev != NULL);
1125                                                 listener->tcp_eager_last_q =
1126                                                     prev;
1127                                         }
1128                                 }
1129                                 tcpp[0] = tcp->tcp_eager_next_q;
1130                                 tcp->tcp_eager_next_q = NULL;
1131                                 tcp->tcp_eager_last_q = NULL;
1132                                 ASSERT(listener->tcp_conn_req_cnt_q > 0);
1133                                 listener->tcp_conn_req_cnt_q--;
1134                                 break;
1135                         }
1136                         prev = tcpp[0];
1137                 }
1138         }
1139         tcp->tcp_listener = NULL;
1140 }
1141 
1142 /* BEGIN CSTYLED */
1143 /*
1144  *
1145  * The sockfs ACCEPT path:
1146  * =======================
1147  *
1148  * The eager is now established in its own perimeter as soon as SYN is
1149  * received in tcp_input_listener(). When sockfs receives conn_ind, it
1150  * completes the accept processing on the acceptor STREAM. The sending
1151  * of conn_ind part is common for both sockfs listener and a TLI/XTI
1152  * listener but a TLI/XTI listener completes the accept processing
1153  * on the listener perimeter.
1154  *
1155  * Common control flow for 3 way handshake:
1156  * ----------------------------------------
1157  *
1158  * incoming SYN (listener perimeter)    -> tcp_input_listener()
1159  *
1160  * incoming SYN-ACK-ACK (eager perim)   -> tcp_input_data()
1161  * send T_CONN_IND (listener perim)     -> tcp_send_conn_ind()
1162  *
1163  * Sockfs ACCEPT Path:
1164  * -------------------
1165  *
1166  * open acceptor stream (tcp_open allocates tcp_tli_accept()
1167  * as STREAM entry point)
1168  *
1169  * soaccept() sends T_CONN_RES on the acceptor STREAM to tcp_tli_accept()
1170  *
1171  * tcp_tli_accept() extracts the eager and makes the q->q_ptr <-> eager
1172  * association (we are not behind eager's squeue but sockfs is protecting us
1173  * and no one knows about this stream yet. The STREAMS entry point q->q_info
1174  * is changed to point at tcp_wput().
1175  *
1176  * tcp_accept_common() sends any deferred eagers via tcp_send_pending() to
1177  * listener (done on listener's perimeter).
1178  *
1179  * tcp_tli_accept() calls tcp_accept_finish() on eagers perimeter to finish
1180  * accept.
1181  *
1182  * TLI/XTI client ACCEPT path:
1183  * ---------------------------
1184  *
1185  * soaccept() sends T_CONN_RES on the listener STREAM.
1186  *
1187  * tcp_tli_accept() -> tcp_accept_swap() complete the processing and send
1188  * a M_SETOPS mblk to eager perimeter to finish accept (tcp_accept_finish()).
1189  *
1190  * Locks:
1191  * ======
1192  *
1193  * listener->tcp_eager_lock protects the listeners->tcp_eager_next_q0 and
1194  * and listeners->tcp_eager_next_q.
1195  *
1196  * Referencing:
1197  * ============
1198  *
1199  * 1) We start out in tcp_input_listener by eager placing a ref on
1200  * listener and listener adding eager to listeners->tcp_eager_next_q0.
1201  *
1202  * 2) When a SYN-ACK-ACK arrives, we send the conn_ind to listener. Before
1203  * doing so we place a ref on the eager. This ref is finally dropped at the
1204  * end of tcp_accept_finish() while unwinding from the squeue, i.e. the
1205  * reference is dropped by the squeue framework.
1206  *
1207  * 3) The ref on listener placed in 1 above is dropped in tcp_accept_finish
1208  *
1209  * The reference must be released by the same entity that added the reference
1210  * In the above scheme, the eager is the entity that adds and releases the
1211  * references. Note that tcp_accept_finish executes in the squeue of the eager
1212  * (albeit after it is attached to the acceptor stream). Though 1. executes
1213  * in the listener's squeue, the eager is nascent at this point and the
1214  * reference can be considered to have been added on behalf of the eager.
1215  *
1216  * Eager getting a Reset or listener closing:
1217  * ==========================================
1218  *
1219  * Once the listener and eager are linked, the listener never does the unlink.
1220  * If the listener needs to close, tcp_eager_cleanup() is called which queues
1221  * a message on all eager perimeter. The eager then does the unlink, clears
1222  * any pointers to the listener's queue and drops the reference to the
1223  * listener. The listener waits in tcp_close outside the squeue until its
1224  * refcount has dropped to 1. This ensures that the listener has waited for
1225  * all eagers to clear their association with the listener.
1226  *
1227  * Similarly, if eager decides to go away, it can unlink itself and close.
1228  * When the T_CONN_RES comes down, we check if eager has closed. Note that
1229  * the reference to eager is still valid because of the extra ref we put
1230  * in tcp_send_conn_ind.
1231  *
1232  * Listener can always locate the eager under the protection
1233  * of the listener->tcp_eager_lock, and then do a refhold
1234  * on the eager during the accept processing.
1235  *
1236  * The acceptor stream accesses the eager in the accept processing
1237  * based on the ref placed on eager before sending T_conn_ind.
1238  * The only entity that can negate this refhold is a listener close
1239  * which is mutually exclusive with an active acceptor stream.
1240  *
1241  * Eager's reference on the listener
1242  * ===================================
1243  *
1244  * If the accept happens (even on a closed eager) the eager drops its
1245  * reference on the listener at the start of tcp_accept_finish. If the
1246  * eager is killed due to an incoming RST before the T_conn_ind is sent up,
1247  * the reference is dropped in tcp_closei_local. If the listener closes,
1248  * the reference is dropped in tcp_eager_kill. In all cases the reference
1249  * is dropped while executing in the eager's context (squeue).
1250  */
1251 /* END CSTYLED */
1252 
1253 /* Process the SYN packet, mp, directed at the listener 'tcp' */
1254 
1255 /*
1256  * THIS FUNCTION IS DIRECTLY CALLED BY IP VIA SQUEUE FOR SYN.
1257  * tcp_input_data will not see any packets for listeners since the listener
1258  * has conn_recv set to tcp_input_listener.
1259  */
1260 /* ARGSUSED */
1261 static void
1262 tcp_input_listener(void *arg, mblk_t *mp, void *arg2, ip_recv_attr_t *ira)
1263 {
1264         tcpha_t         *tcpha;
1265         uint32_t        seg_seq;
1266         tcp_t           *eager;
1267         int             err;
1268         conn_t          *econnp = NULL;
1269         squeue_t        *new_sqp;
1270         mblk_t          *mp1;
1271         uint_t          ip_hdr_len;
1272         conn_t          *lconnp = (conn_t *)arg;
1273         tcp_t           *listener = lconnp->conn_tcp;
1274         tcp_stack_t     *tcps = listener->tcp_tcps;
1275         ip_stack_t      *ipst = tcps->tcps_netstack->netstack_ip;
1276         uint_t          flags;
1277         mblk_t          *tpi_mp;
1278         uint_t          ifindex = ira->ira_ruifindex;
1279         boolean_t       tlc_set = B_FALSE;
1280 
1281         ip_hdr_len = ira->ira_ip_hdr_length;
1282         tcpha = (tcpha_t *)&mp->b_rptr[ip_hdr_len];
1283         flags = (unsigned int)tcpha->tha_flags & 0xFF;
1284 
1285         DTRACE_TCP5(receive, mblk_t *, NULL, ip_xmit_attr_t *, lconnp->conn_ixa,
1286             __dtrace_tcp_void_ip_t *, mp->b_rptr, tcp_t *, listener,
1287             __dtrace_tcp_tcph_t *, tcpha);
1288 
1289         if (!(flags & TH_SYN)) {
1290                 if ((flags & TH_RST) || (flags & TH_URG)) {
1291                         freemsg(mp);
1292                         return;
1293                 }
1294                 if (flags & TH_ACK) {
1295                         /* Note this executes in listener's squeue */
1296                         tcp_xmit_listeners_reset(mp, ira, ipst, lconnp);
1297                         return;
1298                 }
1299 
1300                 freemsg(mp);
1301                 return;
1302         }
1303 
1304         if (listener->tcp_state != TCPS_LISTEN)
1305                 goto error2;
1306 
1307         ASSERT(IPCL_IS_BOUND(lconnp));
1308 
1309         mutex_enter(&listener->tcp_eager_lock);
1310 
1311         /*
1312          * The system is under memory pressure, so we need to do our part
1313          * to relieve the pressure.  So we only accept new request if there
1314          * is nothing waiting to be accepted or waiting to complete the 3-way
1315          * handshake.  This means that busy listener will not get too many
1316          * new requests which they cannot handle in time while non-busy
1317          * listener is still functioning properly.
1318          */
1319         if (tcps->tcps_reclaim && (listener->tcp_conn_req_cnt_q > 0 ||
1320             listener->tcp_conn_req_cnt_q0 > 0)) {
1321                 mutex_exit(&listener->tcp_eager_lock);
1322                 TCP_STAT(tcps, tcp_listen_mem_drop);
1323                 goto error2;
1324         }
1325 
1326         if (listener->tcp_conn_req_cnt_q >= listener->tcp_conn_req_max) {
1327                 mutex_exit(&listener->tcp_eager_lock);
1328                 TCP_STAT(tcps, tcp_listendrop);
1329                 TCPS_BUMP_MIB(tcps, tcpListenDrop);
1330                 if (lconnp->conn_debug) {
1331                         (void) strlog(TCP_MOD_ID, 0, 1, SL_TRACE|SL_ERROR,
1332                             "tcp_input_listener: listen backlog (max=%d) "
1333                             "overflow (%d pending) on %s",
1334                             listener->tcp_conn_req_max,
1335                             listener->tcp_conn_req_cnt_q,
1336                             tcp_display(listener, NULL, DISP_PORT_ONLY));
1337                 }
1338                 goto error2;
1339         }
1340 
1341         if (listener->tcp_conn_req_cnt_q0 >=
1342             listener->tcp_conn_req_max + tcps->tcps_conn_req_max_q0) {
1343                 /*
1344                  * Q0 is full. Drop a pending half-open req from the queue
1345                  * to make room for the new SYN req. Also mark the time we
1346                  * drop a SYN.
1347                  *
1348                  * A more aggressive defense against SYN attack will
1349                  * be to set the "tcp_syn_defense" flag now.
1350                  */
1351                 TCP_STAT(tcps, tcp_listendropq0);
1352                 listener->tcp_last_rcv_lbolt = ddi_get_lbolt64();
1353                 if (!tcp_drop_q0(listener)) {
1354                         mutex_exit(&listener->tcp_eager_lock);
1355                         TCPS_BUMP_MIB(tcps, tcpListenDropQ0);
1356                         if (lconnp->conn_debug) {
1357                                 (void) strlog(TCP_MOD_ID, 0, 3, SL_TRACE,
1358                                     "tcp_input_listener: listen half-open "
1359                                     "queue (max=%d) full (%d pending) on %s",
1360                                     tcps->tcps_conn_req_max_q0,
1361                                     listener->tcp_conn_req_cnt_q0,
1362                                     tcp_display(listener, NULL,
1363                                     DISP_PORT_ONLY));
1364                         }
1365                         goto error2;
1366                 }
1367         }
1368 
1369         /*
1370          * Enforce the limit set on the number of connections per listener.
1371          * Note that tlc_cnt starts with 1.  So need to add 1 to tlc_max
1372          * for comparison.
1373          */
1374         if (listener->tcp_listen_cnt != NULL) {
1375                 tcp_listen_cnt_t *tlc = listener->tcp_listen_cnt;
1376                 int64_t now;
1377 
1378                 if (atomic_inc_32_nv(&tlc->tlc_cnt) > tlc->tlc_max + 1) {
1379                         mutex_exit(&listener->tcp_eager_lock);
1380                         now = ddi_get_lbolt64();
1381                         atomic_dec_32(&tlc->tlc_cnt);
1382                         TCP_STAT(tcps, tcp_listen_cnt_drop);
1383                         tlc->tlc_drop++;
1384                         if (now - tlc->tlc_report_time >
1385                             MSEC_TO_TICK(TCP_TLC_REPORT_INTERVAL)) {
1386                                 zcmn_err(lconnp->conn_zoneid, CE_WARN,
1387                                     "Listener (port %d) connection max (%u) "
1388                                     "reached: %u attempts dropped total\n",
1389                                     ntohs(listener->tcp_connp->conn_lport),
1390                                     tlc->tlc_max, tlc->tlc_drop);
1391                                 tlc->tlc_report_time = now;
1392                         }
1393                         goto error2;
1394                 }
1395                 tlc_set = B_TRUE;
1396         }
1397 
1398         mutex_exit(&listener->tcp_eager_lock);
1399 
1400         /*
1401          * IP sets ira_sqp to either the senders conn_sqp (for loopback)
1402          * or based on the ring (for packets from GLD). Otherwise it is
1403          * set based on lbolt i.e., a somewhat random number.
1404          */
1405         ASSERT(ira->ira_sqp != NULL);
1406         new_sqp = ira->ira_sqp;
1407 
1408         econnp = (conn_t *)tcp_get_conn(arg2, tcps);
1409         if (econnp == NULL)
1410                 goto error2;
1411 
1412         ASSERT(econnp->conn_netstack == lconnp->conn_netstack);
1413         econnp->conn_sqp = new_sqp;
1414         econnp->conn_initial_sqp = new_sqp;
1415         econnp->conn_ixa->ixa_sqp = new_sqp;
1416 
1417         econnp->conn_fport = tcpha->tha_lport;
1418         econnp->conn_lport = tcpha->tha_fport;
1419 
1420         err = conn_inherit_parent(lconnp, econnp);
1421         if (err != 0)
1422                 goto error3;
1423 
1424         /* We already know the laddr of the new connection is ours */
1425         econnp->conn_ixa->ixa_src_generation = ipst->ips_src_generation;
1426 
1427         ASSERT(OK_32PTR(mp->b_rptr));
1428         ASSERT(IPH_HDR_VERSION(mp->b_rptr) == IPV4_VERSION ||
1429             IPH_HDR_VERSION(mp->b_rptr) == IPV6_VERSION);
1430 
1431         if (lconnp->conn_family == AF_INET) {
1432                 ASSERT(IPH_HDR_VERSION(mp->b_rptr) == IPV4_VERSION);
1433                 tpi_mp = tcp_conn_create_v4(lconnp, econnp, mp, ira);
1434         } else {
1435                 tpi_mp = tcp_conn_create_v6(lconnp, econnp, mp, ira);
1436         }
1437 
1438         if (tpi_mp == NULL)
1439                 goto error3;
1440 
1441         eager = econnp->conn_tcp;
1442         eager->tcp_detached = B_TRUE;
1443         SOCK_CONNID_INIT(eager->tcp_connid);
1444 
1445         /*
1446          * Initialize the eager's tcp_t and inherit some parameters from
1447          * the listener.
1448          */
1449         tcp_init_values(eager, listener);
1450 
1451         ASSERT((econnp->conn_ixa->ixa_flags &
1452             (IXAF_SET_ULP_CKSUM | IXAF_VERIFY_SOURCE |
1453             IXAF_VERIFY_PMTU | IXAF_VERIFY_LSO)) ==
1454             (IXAF_SET_ULP_CKSUM | IXAF_VERIFY_SOURCE |
1455             IXAF_VERIFY_PMTU | IXAF_VERIFY_LSO));
1456 
1457         if (!tcps->tcps_dev_flow_ctl)
1458                 econnp->conn_ixa->ixa_flags |= IXAF_NO_DEV_FLOW_CTL;
1459 
1460         /* Prepare for diffing against previous packets */
1461         eager->tcp_recvifindex = 0;
1462         eager->tcp_recvhops = 0xffffffffU;
1463 
1464         if (!(ira->ira_flags & IRAF_IS_IPV4) && econnp->conn_bound_if == 0) {
1465                 if (IN6_IS_ADDR_LINKSCOPE(&econnp->conn_faddr_v6) ||
1466                     IN6_IS_ADDR_LINKSCOPE(&econnp->conn_laddr_v6)) {
1467                         econnp->conn_incoming_ifindex = ifindex;
1468                         econnp->conn_ixa->ixa_flags |= IXAF_SCOPEID_SET;
1469                         econnp->conn_ixa->ixa_scopeid = ifindex;
1470                 }
1471         }
1472 
1473         if ((ira->ira_flags & (IRAF_IS_IPV4|IRAF_IPV4_OPTIONS)) ==
1474             (IRAF_IS_IPV4|IRAF_IPV4_OPTIONS) &&
1475             tcps->tcps_rev_src_routes) {
1476                 ipha_t *ipha = (ipha_t *)mp->b_rptr;
1477                 ip_pkt_t *ipp = &econnp->conn_xmit_ipp;
1478 
1479                 /* Source routing option copyover (reverse it) */
1480                 err = ip_find_hdr_v4(ipha, ipp, B_TRUE);
1481                 if (err != 0) {
1482                         freemsg(tpi_mp);
1483                         goto error3;
1484                 }
1485                 ip_pkt_source_route_reverse_v4(ipp);
1486         }
1487 
1488         ASSERT(eager->tcp_conn.tcp_eager_conn_ind == NULL);
1489         ASSERT(!eager->tcp_tconnind_started);
1490         /*
1491          * If the SYN came with a credential, it's a loopback packet or a
1492          * labeled packet; attach the credential to the TPI message.
1493          */
1494         if (ira->ira_cred != NULL)
1495                 mblk_setcred(tpi_mp, ira->ira_cred, ira->ira_cpid);
1496 
1497         eager->tcp_conn.tcp_eager_conn_ind = tpi_mp;
1498         ASSERT(eager->tcp_ordrel_mp == NULL);
1499 
1500         /* Inherit the listener's non-STREAMS flag */
1501         if (IPCL_IS_NONSTR(lconnp)) {
1502                 econnp->conn_flags |= IPCL_NONSTR;
1503                 /* All non-STREAMS tcp_ts are sockets */
1504                 eager->tcp_issocket = B_TRUE;
1505         } else {
1506                 /*
1507                  * Pre-allocate the T_ordrel_ind mblk for TPI socket so that
1508                  * at close time, we will always have that to send up.
1509                  * Otherwise, we need to do special handling in case the
1510                  * allocation fails at that time.
1511                  */
1512                 if ((eager->tcp_ordrel_mp = mi_tpi_ordrel_ind()) == NULL)
1513                         goto error3;
1514         }
1515         /*
1516          * Now that the IP addresses and ports are setup in econnp we
1517          * can do the IPsec policy work.
1518          */
1519         if (ira->ira_flags & IRAF_IPSEC_SECURE) {
1520                 if (lconnp->conn_policy != NULL) {
1521                         /*
1522                          * Inherit the policy from the listener; use
1523                          * actions from ira
1524                          */
1525                         if (!ip_ipsec_policy_inherit(econnp, lconnp, ira)) {
1526                                 CONN_DEC_REF(econnp);
1527                                 freemsg(mp);
1528                                 goto error3;
1529                         }
1530                 }
1531         }
1532 
1533         /*
1534          * tcp_set_destination() may set tcp_rwnd according to the route
1535          * metrics. If it does not, the eager's receive window will be set
1536          * to the listener's receive window later in this function.
1537          */
1538         eager->tcp_rwnd = 0;
1539 
1540         if (is_system_labeled()) {
1541                 ip_xmit_attr_t *ixa = econnp->conn_ixa;
1542 
1543                 ASSERT(ira->ira_tsl != NULL);
1544                 /* Discard any old label */
1545                 if (ixa->ixa_free_flags & IXA_FREE_TSL) {
1546                         ASSERT(ixa->ixa_tsl != NULL);
1547                         label_rele(ixa->ixa_tsl);
1548                         ixa->ixa_free_flags &= ~IXA_FREE_TSL;
1549                         ixa->ixa_tsl = NULL;
1550                 }
1551                 if ((lconnp->conn_mlp_type != mlptSingle ||
1552                     lconnp->conn_mac_mode != CONN_MAC_DEFAULT) &&
1553                     ira->ira_tsl != NULL) {
1554                         /*
1555                          * If this is an MLP connection or a MAC-Exempt
1556                          * connection with an unlabeled node, packets are to be
1557                          * exchanged using the security label of the received
1558                          * SYN packet instead of the server application's label.
1559                          * tsol_check_dest called from ip_set_destination
1560                          * might later update TSF_UNLABELED by replacing
1561                          * ixa_tsl with a new label.
1562                          */
1563                         label_hold(ira->ira_tsl);
1564                         ip_xmit_attr_replace_tsl(ixa, ira->ira_tsl);
1565                         DTRACE_PROBE2(mlp_syn_accept, conn_t *,
1566                             econnp, ts_label_t *, ixa->ixa_tsl)
1567                 } else {
1568                         ixa->ixa_tsl = crgetlabel(econnp->conn_cred);
1569                         DTRACE_PROBE2(syn_accept, conn_t *,
1570                             econnp, ts_label_t *, ixa->ixa_tsl)
1571                 }
1572                 /*
1573                  * conn_connect() called from tcp_set_destination will verify
1574                  * the destination is allowed to receive packets at the
1575                  * security label of the SYN-ACK we are generating. As part of
1576                  * that, tsol_check_dest() may create a new effective label for
1577                  * this connection.
1578                  * Finally conn_connect() will call conn_update_label.
1579                  * All that remains for TCP to do is to call
1580                  * conn_build_hdr_template which is done as part of
1581                  * tcp_set_destination.
1582                  */
1583         }
1584 
1585         /*
1586          * Since we will clear tcp_listener before we clear tcp_detached
1587          * in the accept code we need tcp_hard_binding aka tcp_accept_inprogress
1588          * so we can tell a TCP_IS_DETACHED_NONEAGER apart.
1589          */
1590         eager->tcp_hard_binding = B_TRUE;
1591 
1592         tcp_bind_hash_insert(&tcps->tcps_bind_fanout[
1593             TCP_BIND_HASH(econnp->conn_lport)], eager, 0);
1594 
1595         CL_INET_CONNECT(econnp, B_FALSE, err);
1596         if (err != 0) {
1597                 tcp_bind_hash_remove(eager);
1598                 goto error3;
1599         }
1600 
1601         SOCK_CONNID_BUMP(eager->tcp_connid);
1602 
1603         /*
1604          * Adapt our mss, ttl, ... based on the remote address.
1605          */
1606 
1607         if (tcp_set_destination(eager) != 0) {
1608                 TCPS_BUMP_MIB(tcps, tcpAttemptFails);
1609                 /* Undo the bind_hash_insert */
1610                 tcp_bind_hash_remove(eager);
1611                 goto error3;
1612         }
1613 
1614         /* Process all TCP options. */
1615         tcp_process_options(eager, tcpha);
1616 
1617         /* Is the other end ECN capable? */
1618         if (tcps->tcps_ecn_permitted >= 1 &&
1619             (tcpha->tha_flags & (TH_ECE|TH_CWR)) == (TH_ECE|TH_CWR)) {
1620                 eager->tcp_ecn_ok = B_TRUE;
1621         }
1622 
1623         /*
1624          * The listener's conn_rcvbuf should be the default window size or a
1625          * window size changed via SO_RCVBUF option. First round up the
1626          * eager's tcp_rwnd to the nearest MSS. Then find out the window
1627          * scale option value if needed. Call tcp_rwnd_set() to finish the
1628          * setting.
1629          *
1630          * Note if there is a rpipe metric associated with the remote host,
1631          * we should not inherit receive window size from listener.
1632          */
1633         eager->tcp_rwnd = MSS_ROUNDUP(
1634             (eager->tcp_rwnd == 0 ? econnp->conn_rcvbuf :
1635             eager->tcp_rwnd), eager->tcp_mss);
1636         if (eager->tcp_snd_ws_ok)
1637                 tcp_set_ws_value(eager);
1638         /*
1639          * Note that this is the only place tcp_rwnd_set() is called for
1640          * accepting a connection.  We need to call it here instead of
1641          * after the 3-way handshake because we need to tell the other
1642          * side our rwnd in the SYN-ACK segment.
1643          */
1644         (void) tcp_rwnd_set(eager, eager->tcp_rwnd);
1645 
1646         ASSERT(eager->tcp_connp->conn_rcvbuf != 0 &&
1647             eager->tcp_connp->conn_rcvbuf == eager->tcp_rwnd);
1648 
1649         ASSERT(econnp->conn_rcvbuf != 0 &&
1650             econnp->conn_rcvbuf == eager->tcp_rwnd);
1651 
1652         /* Put a ref on the listener for the eager. */
1653         CONN_INC_REF(lconnp);
1654         mutex_enter(&listener->tcp_eager_lock);
1655         listener->tcp_eager_next_q0->tcp_eager_prev_q0 = eager;
1656         eager->tcp_eager_next_q0 = listener->tcp_eager_next_q0;
1657         listener->tcp_eager_next_q0 = eager;
1658         eager->tcp_eager_prev_q0 = listener;
1659 
1660         /* Set tcp_listener before adding it to tcp_conn_fanout */
1661         eager->tcp_listener = listener;
1662         eager->tcp_saved_listener = listener;
1663 
1664         /*
1665          * Set tcp_listen_cnt so that when the connection is done, the counter
1666          * is decremented.
1667          */
1668         eager->tcp_listen_cnt = listener->tcp_listen_cnt;
1669 
1670         /*
1671          * Tag this detached tcp vector for later retrieval
1672          * by our listener client in tcp_accept().
1673          */
1674         eager->tcp_conn_req_seqnum = listener->tcp_conn_req_seqnum;
1675         listener->tcp_conn_req_cnt_q0++;
1676         if (++listener->tcp_conn_req_seqnum == -1) {
1677                 /*
1678                  * -1 is "special" and defined in TPI as something
1679                  * that should never be used in T_CONN_IND
1680                  */
1681                 ++listener->tcp_conn_req_seqnum;
1682         }
1683         mutex_exit(&listener->tcp_eager_lock);
1684 
1685         if (listener->tcp_syn_defense) {
1686                 /* Don't drop the SYN that comes from a good IP source */
1687                 ipaddr_t *addr_cache;
1688 
1689                 addr_cache = (ipaddr_t *)(listener->tcp_ip_addr_cache);
1690                 if (addr_cache != NULL && econnp->conn_faddr_v4 ==
1691                     addr_cache[IP_ADDR_CACHE_HASH(econnp->conn_faddr_v4)]) {
1692                         eager->tcp_dontdrop = B_TRUE;
1693                 }
1694         }
1695 
1696         /*
1697          * We need to insert the eager in its own perimeter but as soon
1698          * as we do that, we expose the eager to the classifier and
1699          * should not touch any field outside the eager's perimeter.
1700          * So do all the work necessary before inserting the eager
1701          * in its own perimeter. Be optimistic that conn_connect()
1702          * will succeed but undo everything if it fails.
1703          */
1704         seg_seq = ntohl(tcpha->tha_seq);
1705         eager->tcp_irs = seg_seq;
1706         eager->tcp_rack = seg_seq;
1707         eager->tcp_rnxt = seg_seq + 1;
1708         eager->tcp_tcpha->tha_ack = htonl(eager->tcp_rnxt);
1709         TCPS_BUMP_MIB(tcps, tcpPassiveOpens);
1710         eager->tcp_state = TCPS_SYN_RCVD;
1711         DTRACE_TCP6(state__change, void, NULL, ip_xmit_attr_t *,
1712             econnp->conn_ixa, void, NULL, tcp_t *, eager, void, NULL,
1713             int32_t, TCPS_LISTEN);
1714 
1715         mp1 = tcp_xmit_mp(eager, eager->tcp_xmit_head, eager->tcp_mss,
1716             NULL, NULL, eager->tcp_iss, B_FALSE, NULL, B_FALSE);
1717         if (mp1 == NULL) {
1718                 /*
1719                  * Increment the ref count as we are going to
1720                  * enqueueing an mp in squeue
1721                  */
1722                 CONN_INC_REF(econnp);
1723                 goto error;
1724         }
1725 
1726         /*
1727          * We need to start the rto timer. In normal case, we start
1728          * the timer after sending the packet on the wire (or at
1729          * least believing that packet was sent by waiting for
1730          * conn_ip_output() to return). Since this is the first packet
1731          * being sent on the wire for the eager, our initial tcp_rto
1732          * is at least tcp_rexmit_interval_min which is a fairly
1733          * large value to allow the algorithm to adjust slowly to large
1734          * fluctuations of RTT during first few transmissions.
1735          *
1736          * Starting the timer first and then sending the packet in this
1737          * case shouldn't make much difference since tcp_rexmit_interval_min
1738          * is of the order of several 100ms and starting the timer
1739          * first and then sending the packet will result in difference
1740          * of few micro seconds.
1741          *
1742          * Without this optimization, we are forced to hold the fanout
1743          * lock across the ipcl_bind_insert() and sending the packet
1744          * so that we don't race against an incoming packet (maybe RST)
1745          * for this eager.
1746          *
1747          * It is necessary to acquire an extra reference on the eager
1748          * at this point and hold it until after tcp_send_data() to
1749          * ensure against an eager close race.
1750          */
1751 
1752         CONN_INC_REF(econnp);
1753 
1754         TCP_TIMER_RESTART(eager, eager->tcp_rto);
1755 
1756         /*
1757          * Insert the eager in its own perimeter now. We are ready to deal
1758          * with any packets on eager.
1759          */
1760         if (ipcl_conn_insert(econnp) != 0)
1761                 goto error;
1762 
1763         ASSERT(econnp->conn_ixa->ixa_notify_cookie == econnp->conn_tcp);
1764         freemsg(mp);
1765         /*
1766          * Send the SYN-ACK. Use the right squeue so that conn_ixa is
1767          * only used by one thread at a time.
1768          */
1769         if (econnp->conn_sqp == lconnp->conn_sqp) {
1770                 DTRACE_TCP5(send, mblk_t *, NULL, ip_xmit_attr_t *,
1771                     econnp->conn_ixa, __dtrace_tcp_void_ip_t *, mp1->b_rptr,
1772                     tcp_t *, eager, __dtrace_tcp_tcph_t *,
1773                     &mp1->b_rptr[econnp->conn_ixa->ixa_ip_hdr_length]);
1774                 (void) conn_ip_output(mp1, econnp->conn_ixa);
1775                 CONN_DEC_REF(econnp);
1776         } else {
1777                 SQUEUE_ENTER_ONE(econnp->conn_sqp, mp1, tcp_send_synack,
1778                     econnp, NULL, SQ_PROCESS, SQTAG_TCP_SEND_SYNACK);
1779         }
1780         return;
1781 error:
1782         freemsg(mp1);
1783         eager->tcp_closemp_used = B_TRUE;
1784         TCP_DEBUG_GETPCSTACK(eager->tcmp_stk, 15);
1785         mp1 = &eager->tcp_closemp;
1786         SQUEUE_ENTER_ONE(econnp->conn_sqp, mp1, tcp_eager_kill,
1787             econnp, NULL, SQ_FILL, SQTAG_TCP_CONN_REQ_2);
1788 
1789         /*
1790          * If a connection already exists, send the mp to that connections so
1791          * that it can be appropriately dealt with.
1792          */
1793         ipst = tcps->tcps_netstack->netstack_ip;
1794 
1795         if ((econnp = ipcl_classify(mp, ira, ipst)) != NULL) {
1796                 if (!IPCL_IS_CONNECTED(econnp)) {
1797                         /*
1798                          * Something bad happened. ipcl_conn_insert()
1799                          * failed because a connection already existed
1800                          * in connected hash but we can't find it
1801                          * anymore (someone blew it away). Just
1802                          * free this message and hopefully remote
1803                          * will retransmit at which time the SYN can be
1804                          * treated as a new connection or dealth with
1805                          * a TH_RST if a connection already exists.
1806                          */
1807                         CONN_DEC_REF(econnp);
1808                         freemsg(mp);
1809                 } else {
1810                         SQUEUE_ENTER_ONE(econnp->conn_sqp, mp, tcp_input_data,
1811                             econnp, ira, SQ_FILL, SQTAG_TCP_CONN_REQ_1);
1812                 }
1813         } else {
1814                 /* Nobody wants this packet */
1815                 freemsg(mp);
1816         }
1817         return;
1818 error3:
1819         CONN_DEC_REF(econnp);
1820 error2:
1821         freemsg(mp);
1822         if (tlc_set)
1823                 atomic_dec_32(&listener->tcp_listen_cnt->tlc_cnt);
1824 }
1825 
1826 /*
1827  * In an ideal case of vertical partition in NUMA architecture, its
1828  * beneficial to have the listener and all the incoming connections
1829  * tied to the same squeue. The other constraint is that incoming
1830  * connections should be tied to the squeue attached to interrupted
1831  * CPU for obvious locality reason so this leaves the listener to
1832  * be tied to the same squeue. Our only problem is that when listener
1833  * is binding, the CPU that will get interrupted by the NIC whose
1834  * IP address the listener is binding to is not even known. So
1835  * the code below allows us to change that binding at the time the
1836  * CPU is interrupted by virtue of incoming connection's squeue.
1837  *
1838  * This is usefull only in case of a listener bound to a specific IP
1839  * address. For other kind of listeners, they get bound the
1840  * very first time and there is no attempt to rebind them.
1841  */
1842 void
1843 tcp_input_listener_unbound(void *arg, mblk_t *mp, void *arg2,
1844     ip_recv_attr_t *ira)
1845 {
1846         conn_t          *connp = (conn_t *)arg;
1847         squeue_t        *sqp = (squeue_t *)arg2;
1848         squeue_t        *new_sqp;
1849         uint32_t        conn_flags;
1850 
1851         /*
1852          * IP sets ira_sqp to either the senders conn_sqp (for loopback)
1853          * or based on the ring (for packets from GLD). Otherwise it is
1854          * set based on lbolt i.e., a somewhat random number.
1855          */
1856         ASSERT(ira->ira_sqp != NULL);
1857         new_sqp = ira->ira_sqp;
1858 
1859         if (connp->conn_fanout == NULL)
1860                 goto done;
1861 
1862         if (!(connp->conn_flags & IPCL_FULLY_BOUND)) {
1863                 mutex_enter(&connp->conn_fanout->connf_lock);
1864                 mutex_enter(&connp->conn_lock);
1865                 /*
1866                  * No one from read or write side can access us now
1867                  * except for already queued packets on this squeue.
1868                  * But since we haven't changed the squeue yet, they
1869                  * can't execute. If they are processed after we have
1870                  * changed the squeue, they are sent back to the
1871                  * correct squeue down below.
1872                  * But a listner close can race with processing of
1873                  * incoming SYN. If incoming SYN processing changes
1874                  * the squeue then the listener close which is waiting
1875                  * to enter the squeue would operate on the wrong
1876                  * squeue. Hence we don't change the squeue here unless
1877                  * the refcount is exactly the minimum refcount. The
1878                  * minimum refcount of 4 is counted as - 1 each for
1879                  * TCP and IP, 1 for being in the classifier hash, and
1880                  * 1 for the mblk being processed.
1881                  */
1882 
1883                 if (connp->conn_ref != 4 ||
1884                     connp->conn_tcp->tcp_state != TCPS_LISTEN) {
1885                         mutex_exit(&connp->conn_lock);
1886                         mutex_exit(&connp->conn_fanout->connf_lock);
1887                         goto done;
1888                 }
1889                 if (connp->conn_sqp != new_sqp) {
1890                         while (connp->conn_sqp != new_sqp)
1891                                 (void) atomic_cas_ptr(&connp->conn_sqp, sqp,
1892                                     new_sqp);
1893                         /* No special MT issues for outbound ixa_sqp hint */
1894                         connp->conn_ixa->ixa_sqp = new_sqp;
1895                 }
1896 
1897                 do {
1898                         conn_flags = connp->conn_flags;
1899                         conn_flags |= IPCL_FULLY_BOUND;
1900                         (void) atomic_cas_32(&connp->conn_flags,
1901                             connp->conn_flags, conn_flags);
1902                 } while (!(connp->conn_flags & IPCL_FULLY_BOUND));
1903 
1904                 mutex_exit(&connp->conn_fanout->connf_lock);
1905                 mutex_exit(&connp->conn_lock);
1906 
1907                 /*
1908                  * Assume we have picked a good squeue for the listener. Make
1909                  * subsequent SYNs not try to change the squeue.
1910                  */
1911                 connp->conn_recv = tcp_input_listener;
1912         }
1913 
1914 done:
1915         if (connp->conn_sqp != sqp) {
1916                 CONN_INC_REF(connp);
1917                 SQUEUE_ENTER_ONE(connp->conn_sqp, mp, connp->conn_recv, connp,
1918                     ira, SQ_FILL, SQTAG_TCP_CONN_REQ_UNBOUND);
1919         } else {
1920                 tcp_input_listener(connp, mp, sqp, ira);
1921         }
1922 }
1923 
1924 /*
1925  * Send up all messages queued on tcp_rcv_list.
1926  */
1927 uint_t
1928 tcp_rcv_drain(tcp_t *tcp)
1929 {
1930         mblk_t *mp;
1931         uint_t ret = 0;
1932 #ifdef DEBUG
1933         uint_t cnt = 0;
1934 #endif
1935         queue_t *q = tcp->tcp_connp->conn_rq;
1936 
1937         /* Can't drain on an eager connection */
1938         if (tcp->tcp_listener != NULL)
1939                 return (ret);
1940 
1941         /* Can't be a non-STREAMS connection */
1942         ASSERT(!IPCL_IS_NONSTR(tcp->tcp_connp));
1943 
1944         /* No need for the push timer now. */
1945         if (tcp->tcp_push_tid != 0) {
1946                 (void) TCP_TIMER_CANCEL(tcp, tcp->tcp_push_tid);
1947                 tcp->tcp_push_tid = 0;
1948         }
1949 
1950         /*
1951          * Handle two cases here: we are currently fused or we were
1952          * previously fused and have some urgent data to be delivered
1953          * upstream.  The latter happens because we either ran out of
1954          * memory or were detached and therefore sending the SIGURG was
1955          * deferred until this point.  In either case we pass control
1956          * over to tcp_fuse_rcv_drain() since it may need to complete
1957          * some work.
1958          */
1959         if ((tcp->tcp_fused || tcp->tcp_fused_sigurg)) {
1960                 if (tcp_fuse_rcv_drain(q, tcp, tcp->tcp_fused ? NULL :
1961                     &tcp->tcp_fused_sigurg_mp))
1962                         return (ret);
1963         }
1964 
1965         while ((mp = tcp->tcp_rcv_list) != NULL) {
1966                 tcp->tcp_rcv_list = mp->b_next;
1967                 mp->b_next = NULL;
1968 #ifdef DEBUG
1969                 cnt += msgdsize(mp);
1970 #endif
1971                 putnext(q, mp);
1972         }
1973 #ifdef DEBUG
1974         ASSERT(cnt == tcp->tcp_rcv_cnt);
1975 #endif
1976         tcp->tcp_rcv_last_head = NULL;
1977         tcp->tcp_rcv_last_tail = NULL;
1978         tcp->tcp_rcv_cnt = 0;
1979 
1980         if (canputnext(q))
1981                 return (tcp_rwnd_reopen(tcp));
1982 
1983         return (ret);
1984 }
1985 
1986 /*
1987  * Queue data on tcp_rcv_list which is a b_next chain.
1988  * tcp_rcv_last_head/tail is the last element of this chain.
1989  * Each element of the chain is a b_cont chain.
1990  *
1991  * M_DATA messages are added to the current element.
1992  * Other messages are added as new (b_next) elements.
1993  */
1994 void
1995 tcp_rcv_enqueue(tcp_t *tcp, mblk_t *mp, uint_t seg_len, cred_t *cr)
1996 {
1997         ASSERT(seg_len == msgdsize(mp));
1998         ASSERT(tcp->tcp_rcv_list == NULL || tcp->tcp_rcv_last_head != NULL);
1999 
2000         if (is_system_labeled()) {
2001                 ASSERT(cr != NULL || msg_getcred(mp, NULL) != NULL);
2002                 /*
2003                  * Provide for protocols above TCP such as RPC. NOPID leaves
2004                  * db_cpid unchanged.
2005                  * The cred could have already been set.
2006                  */
2007                 if (cr != NULL)
2008                         mblk_setcred(mp, cr, NOPID);
2009         }
2010 
2011         if (tcp->tcp_rcv_list == NULL) {
2012                 ASSERT(tcp->tcp_rcv_last_head == NULL);
2013                 tcp->tcp_rcv_list = mp;
2014                 tcp->tcp_rcv_last_head = mp;
2015         } else if (DB_TYPE(mp) == DB_TYPE(tcp->tcp_rcv_last_head)) {
2016                 tcp->tcp_rcv_last_tail->b_cont = mp;
2017         } else {
2018                 tcp->tcp_rcv_last_head->b_next = mp;
2019                 tcp->tcp_rcv_last_head = mp;
2020         }
2021 
2022         while (mp->b_cont)
2023                 mp = mp->b_cont;
2024 
2025         tcp->tcp_rcv_last_tail = mp;
2026         tcp->tcp_rcv_cnt += seg_len;
2027         tcp->tcp_rwnd -= seg_len;
2028 }
2029 
2030 /* Generate an ACK-only (no data) segment for a TCP endpoint */
2031 mblk_t *
2032 tcp_ack_mp(tcp_t *tcp)
2033 {
2034         uint32_t        seq_no;
2035         tcp_stack_t     *tcps = tcp->tcp_tcps;
2036         conn_t          *connp = tcp->tcp_connp;
2037 
2038         /*
2039          * There are a few cases to be considered while setting the sequence no.
2040          * Essentially, we can come here while processing an unacceptable pkt
2041          * in the TCPS_SYN_RCVD state, in which case we set the sequence number
2042          * to snxt (per RFC 793), note the swnd wouldn't have been set yet.
2043          * If we are here for a zero window probe, stick with suna. In all
2044          * other cases, we check if suna + swnd encompasses snxt and set
2045          * the sequence number to snxt, if so. If snxt falls outside the
2046          * window (the receiver probably shrunk its window), we will go with
2047          * suna + swnd, otherwise the sequence no will be unacceptable to the
2048          * receiver.
2049          */
2050         if (tcp->tcp_zero_win_probe) {
2051                 seq_no = tcp->tcp_suna;
2052         } else if (tcp->tcp_state == TCPS_SYN_RCVD) {
2053                 ASSERT(tcp->tcp_swnd == 0);
2054                 seq_no = tcp->tcp_snxt;
2055         } else {
2056                 seq_no = SEQ_GT(tcp->tcp_snxt,
2057                     (tcp->tcp_suna + tcp->tcp_swnd)) ?
2058                     (tcp->tcp_suna + tcp->tcp_swnd) : tcp->tcp_snxt;
2059         }
2060 
2061         if (tcp->tcp_valid_bits) {
2062                 /*
2063                  * For the complex case where we have to send some
2064                  * controls (FIN or SYN), let tcp_xmit_mp do it.
2065                  */
2066                 return (tcp_xmit_mp(tcp, NULL, 0, NULL, NULL, seq_no, B_FALSE,
2067                     NULL, B_FALSE));
2068         } else {
2069                 /* Generate a simple ACK */
2070                 int     data_length;
2071                 uchar_t *rptr;
2072                 tcpha_t *tcpha;
2073                 mblk_t  *mp1;
2074                 int32_t total_hdr_len;
2075                 int32_t tcp_hdr_len;
2076                 int32_t num_sack_blk = 0;
2077                 int32_t sack_opt_len;
2078                 ip_xmit_attr_t *ixa = connp->conn_ixa;
2079 
2080                 /*
2081                  * Allocate space for TCP + IP headers
2082                  * and link-level header
2083                  */
2084                 if (tcp->tcp_snd_sack_ok && tcp->tcp_num_sack_blk > 0) {
2085                         num_sack_blk = MIN(tcp->tcp_max_sack_blk,
2086                             tcp->tcp_num_sack_blk);
2087                         sack_opt_len = num_sack_blk * sizeof (sack_blk_t) +
2088                             TCPOPT_NOP_LEN * 2 + TCPOPT_HEADER_LEN;
2089                         total_hdr_len = connp->conn_ht_iphc_len + sack_opt_len;
2090                         tcp_hdr_len = connp->conn_ht_ulp_len + sack_opt_len;
2091                 } else {
2092                         total_hdr_len = connp->conn_ht_iphc_len;
2093                         tcp_hdr_len = connp->conn_ht_ulp_len;
2094                 }
2095                 mp1 = allocb(total_hdr_len + tcps->tcps_wroff_xtra, BPRI_MED);
2096                 if (!mp1)
2097                         return (NULL);
2098 
2099                 /* Update the latest receive window size in TCP header. */
2100                 tcp->tcp_tcpha->tha_win =
2101                     htons(tcp->tcp_rwnd >> tcp->tcp_rcv_ws);
2102                 /* copy in prototype TCP + IP header */
2103                 rptr = mp1->b_rptr + tcps->tcps_wroff_xtra;
2104                 mp1->b_rptr = rptr;
2105                 mp1->b_wptr = rptr + total_hdr_len;
2106                 bcopy(connp->conn_ht_iphc, rptr, connp->conn_ht_iphc_len);
2107 
2108                 tcpha = (tcpha_t *)&rptr[ixa->ixa_ip_hdr_length];
2109 
2110                 /* Set the TCP sequence number. */
2111                 tcpha->tha_seq = htonl(seq_no);
2112 
2113                 /* Set up the TCP flag field. */
2114                 tcpha->tha_flags = (uchar_t)TH_ACK;
2115                 if (tcp->tcp_ecn_echo_on)
2116                         tcpha->tha_flags |= TH_ECE;
2117 
2118                 tcp->tcp_rack = tcp->tcp_rnxt;
2119                 tcp->tcp_rack_cnt = 0;
2120 
2121                 /* fill in timestamp option if in use */
2122                 if (tcp->tcp_snd_ts_ok) {
2123                         uint32_t llbolt = (uint32_t)LBOLT_FASTPATH;
2124 
2125                         U32_TO_BE32(llbolt,
2126                             (char *)tcpha + TCP_MIN_HEADER_LENGTH+4);
2127                         U32_TO_BE32(tcp->tcp_ts_recent,
2128                             (char *)tcpha + TCP_MIN_HEADER_LENGTH+8);
2129                 }
2130 
2131                 /* Fill in SACK options */
2132                 if (num_sack_blk > 0) {
2133                         uchar_t *wptr = (uchar_t *)tcpha +
2134                             connp->conn_ht_ulp_len;
2135                         sack_blk_t *tmp;
2136                         int32_t i;
2137 
2138                         wptr[0] = TCPOPT_NOP;
2139                         wptr[1] = TCPOPT_NOP;
2140                         wptr[2] = TCPOPT_SACK;
2141                         wptr[3] = TCPOPT_HEADER_LEN + num_sack_blk *
2142                             sizeof (sack_blk_t);
2143                         wptr += TCPOPT_REAL_SACK_LEN;
2144 
2145                         tmp = tcp->tcp_sack_list;
2146                         for (i = 0; i < num_sack_blk; i++) {
2147                                 U32_TO_BE32(tmp[i].begin, wptr);
2148                                 wptr += sizeof (tcp_seq);
2149                                 U32_TO_BE32(tmp[i].end, wptr);
2150                                 wptr += sizeof (tcp_seq);
2151                         }
2152                         tcpha->tha_offset_and_reserved +=
2153                             ((num_sack_blk * 2 + 1) << 4);
2154                 }
2155 
2156                 ixa->ixa_pktlen = total_hdr_len;
2157 
2158                 if (ixa->ixa_flags & IXAF_IS_IPV4) {
2159                         ((ipha_t *)rptr)->ipha_length = htons(total_hdr_len);
2160                 } else {
2161                         ip6_t *ip6 = (ip6_t *)rptr;
2162 
2163                         ip6->ip6_plen = htons(total_hdr_len - IPV6_HDR_LEN);
2164                 }
2165 
2166                 /*
2167                  * Prime pump for checksum calculation in IP.  Include the
2168                  * adjustment for a source route if any.
2169                  */
2170                 data_length = tcp_hdr_len + connp->conn_sum;
2171                 data_length = (data_length >> 16) + (data_length & 0xFFFF);
2172                 tcpha->tha_sum = htons(data_length);
2173 
2174                 if (tcp->tcp_ip_forward_progress) {
2175                         tcp->tcp_ip_forward_progress = B_FALSE;
2176                         connp->conn_ixa->ixa_flags |= IXAF_REACH_CONF;
2177                 } else {
2178                         connp->conn_ixa->ixa_flags &= ~IXAF_REACH_CONF;
2179                 }
2180                 return (mp1);
2181         }
2182 }
2183 
2184 /*
2185  * Dummy socket upcalls for if/when the conn_t gets detached from a
2186  * direct-callback sonode via a user-driven close().  Easy to catch with
2187  * DTrace FBT, and should be mostly harmless.
2188  */
2189 
2190 /* ARGSUSED */
2191 static sock_upper_handle_t
2192 tcp_dummy_newconn(sock_upper_handle_t x, sock_lower_handle_t y,
2193     sock_downcalls_t *z, cred_t *cr, pid_t pid, sock_upcalls_t **ignored)
2194 {
2195         ASSERT(0);      /* Panic in debug, otherwise ignore. */
2196         return (NULL);
2197 }
2198 
2199 /* ARGSUSED */
2200 static void
2201 tcp_dummy_connected(sock_upper_handle_t x, sock_connid_t y, cred_t *cr,
2202     pid_t pid)
2203 {
2204         ASSERT(x == NULL);
2205         /* Normally we'd crhold(cr) and attach it to socket state. */
2206         /* LINTED */
2207 }
2208 
2209 /* ARGSUSED */
2210 static int
2211 tcp_dummy_disconnected(sock_upper_handle_t x, sock_connid_t y, int blah)
2212 {
2213         ASSERT(0);      /* Panic in debug, otherwise ignore. */
2214         return (-1);
2215 }
2216 
2217 /* ARGSUSED */
2218 static void
2219 tcp_dummy_opctl(sock_upper_handle_t x, sock_opctl_action_t y, uintptr_t blah)
2220 {
2221         ASSERT(x == NULL);
2222         /* We really want this one to be a harmless NOP for now. */
2223         /* LINTED */
2224 }
2225 
2226 /* ARGSUSED */
2227 static ssize_t
2228 tcp_dummy_recv(sock_upper_handle_t x, mblk_t *mp, size_t len, int flags,
2229     int *error, boolean_t *push)
2230 {
2231         ASSERT(x == NULL);
2232 
2233         /*
2234          * Consume the message, set ESHUTDOWN, and return an error.
2235          * Nobody's home!
2236          */
2237         freemsg(mp);
2238         *error = ESHUTDOWN;
2239         return (-1);
2240 }
2241 
2242 /* ARGSUSED */
2243 static void
2244 tcp_dummy_set_proto_props(sock_upper_handle_t x, struct sock_proto_props *y)
2245 {
2246         ASSERT(0);      /* Panic in debug, otherwise ignore. */
2247 }
2248 
2249 /* ARGSUSED */
2250 static void
2251 tcp_dummy_txq_full(sock_upper_handle_t x, boolean_t y)
2252 {
2253         ASSERT(0);      /* Panic in debug, otherwise ignore. */
2254 }
2255 
2256 /* ARGSUSED */
2257 static void
2258 tcp_dummy_signal_oob(sock_upper_handle_t x, ssize_t len)
2259 {
2260         ASSERT(x == NULL);
2261         /* Otherwise, this would signal socket state about OOB data. */
2262 }
2263 
2264 /* ARGSUSED */
2265 static void
2266 tcp_dummy_set_error(sock_upper_handle_t x, int err)
2267 {
2268         ASSERT(0);      /* Panic in debug, otherwise ignore. */
2269 }
2270 
2271 /* ARGSUSED */
2272 static void
2273 tcp_dummy_onearg(sock_upper_handle_t x)
2274 {
2275         ASSERT(0);      /* Panic in debug, otherwise ignore. */
2276 }
2277 
2278 static sock_upcalls_t tcp_dummy_upcalls = {
2279         tcp_dummy_newconn,
2280         tcp_dummy_connected,
2281         tcp_dummy_disconnected,
2282         tcp_dummy_opctl,
2283         tcp_dummy_recv,
2284         tcp_dummy_set_proto_props,
2285         tcp_dummy_txq_full,
2286         tcp_dummy_signal_oob,
2287         tcp_dummy_onearg,
2288         tcp_dummy_set_error,
2289         tcp_dummy_onearg
2290 };
2291 
2292 /*
2293  * Handle M_DATA messages from IP. Its called directly from IP via
2294  * squeue for received IP packets.
2295  *
2296  * The first argument is always the connp/tcp to which the mp belongs.
2297  * There are no exceptions to this rule. The caller has already put
2298  * a reference on this connp/tcp and once tcp_input_data() returns,
2299  * the squeue will do the refrele.
2300  *
2301  * The TH_SYN for the listener directly go to tcp_input_listener via
2302  * squeue. ICMP errors go directly to tcp_icmp_input().
2303  *
2304  * sqp: NULL = recursive, sqp != NULL means called from squeue
2305  */
2306 void
2307 tcp_input_data(void *arg, mblk_t *mp, void *arg2, ip_recv_attr_t *ira)
2308 {
2309         int32_t         bytes_acked;
2310         int32_t         gap;
2311         mblk_t          *mp1;
2312         uint_t          flags;
2313         uint32_t        new_swnd = 0;
2314         uchar_t         *iphdr;
2315         uchar_t         *rptr;
2316         int32_t         rgap;
2317         uint32_t        seg_ack;
2318         int             seg_len;
2319         uint_t          ip_hdr_len;
2320         uint32_t        seg_seq;
2321         tcpha_t         *tcpha;
2322         int             urp;
2323         tcp_opt_t       tcpopt;
2324         ip_pkt_t        ipp;
2325         boolean_t       ofo_seg = B_FALSE; /* Out of order segment */
2326         uint32_t        cwnd;
2327         uint32_t        add;
2328         int             npkt;
2329         int             mss;
2330         conn_t          *connp = (conn_t *)arg;
2331         squeue_t        *sqp = (squeue_t *)arg2;
2332         tcp_t           *tcp = connp->conn_tcp;
2333         tcp_stack_t     *tcps = tcp->tcp_tcps;
2334         sock_upcalls_t  *sockupcalls;
2335 
2336         /*
2337          * RST from fused tcp loopback peer should trigger an unfuse.
2338          */
2339         if (tcp->tcp_fused) {
2340                 TCP_STAT(tcps, tcp_fusion_aborted);
2341                 tcp_unfuse(tcp);
2342         }
2343 
2344         iphdr = mp->b_rptr;
2345         rptr = mp->b_rptr;
2346         ASSERT(OK_32PTR(rptr));
2347 
2348         ip_hdr_len = ira->ira_ip_hdr_length;
2349         if (connp->conn_recv_ancillary.crb_all != 0) {
2350                 /*
2351                  * Record packet information in the ip_pkt_t
2352                  */
2353                 ipp.ipp_fields = 0;
2354                 if (ira->ira_flags & IRAF_IS_IPV4) {
2355                         (void) ip_find_hdr_v4((ipha_t *)rptr, &ipp,
2356                             B_FALSE);
2357                 } else {
2358                         uint8_t nexthdrp;
2359 
2360                         /*
2361                          * IPv6 packets can only be received by applications
2362                          * that are prepared to receive IPv6 addresses.
2363                          * The IP fanout must ensure this.
2364                          */
2365                         ASSERT(connp->conn_family == AF_INET6);
2366 
2367                         (void) ip_find_hdr_v6(mp, (ip6_t *)rptr, B_TRUE, &ipp,
2368                             &nexthdrp);
2369                         ASSERT(nexthdrp == IPPROTO_TCP);
2370 
2371                         /* Could have caused a pullup? */
2372                         iphdr = mp->b_rptr;
2373                         rptr = mp->b_rptr;
2374                 }
2375         }
2376         ASSERT(DB_TYPE(mp) == M_DATA);
2377         ASSERT(mp->b_next == NULL);
2378 
2379         tcpha = (tcpha_t *)&rptr[ip_hdr_len];
2380         seg_seq = ntohl(tcpha->tha_seq);
2381         seg_ack = ntohl(tcpha->tha_ack);
2382         ASSERT((uintptr_t)(mp->b_wptr - rptr) <= (uintptr_t)INT_MAX);
2383         seg_len = (int)(mp->b_wptr - rptr) -
2384             (ip_hdr_len + TCP_HDR_LENGTH(tcpha));
2385         if ((mp1 = mp->b_cont) != NULL && mp1->b_datap->db_type == M_DATA) {
2386                 do {
2387                         ASSERT((uintptr_t)(mp1->b_wptr - mp1->b_rptr) <=
2388                             (uintptr_t)INT_MAX);
2389                         seg_len += (int)(mp1->b_wptr - mp1->b_rptr);
2390                 } while ((mp1 = mp1->b_cont) != NULL &&
2391                     mp1->b_datap->db_type == M_DATA);
2392         }
2393 
2394         DTRACE_TCP5(receive, mblk_t *, NULL, ip_xmit_attr_t *, connp->conn_ixa,
2395             __dtrace_tcp_void_ip_t *, iphdr, tcp_t *, tcp,
2396             __dtrace_tcp_tcph_t *, tcpha);
2397 
2398         if (tcp->tcp_state == TCPS_TIME_WAIT) {
2399                 tcp_time_wait_processing(tcp, mp, seg_seq, seg_ack,
2400                     seg_len, tcpha, ira);
2401                 return;
2402         }
2403 
2404         if (sqp != NULL) {
2405                 /*
2406                  * This is the correct place to update tcp_last_recv_time. Note
2407                  * that it is also updated for tcp structure that belongs to
2408                  * global and listener queues which do not really need updating.
2409                  * But that should not cause any harm.  And it is updated for
2410                  * all kinds of incoming segments, not only for data segments.
2411                  */
2412                 tcp->tcp_last_recv_time = LBOLT_FASTPATH;
2413         }
2414 
2415         flags = (unsigned int)tcpha->tha_flags & 0xFF;
2416 
2417         BUMP_LOCAL(tcp->tcp_ibsegs);
2418         DTRACE_PROBE2(tcp__trace__recv, mblk_t *, mp, tcp_t *, tcp);
2419 
2420         if ((flags & TH_URG) && sqp != NULL) {
2421                 /*
2422                  * TCP can't handle urgent pointers that arrive before
2423                  * the connection has been accept()ed since it can't
2424                  * buffer OOB data.  Discard segment if this happens.
2425                  *
2426                  * We can't just rely on a non-null tcp_listener to indicate
2427                  * that the accept() has completed since unlinking of the
2428                  * eager and completion of the accept are not atomic.
2429                  * tcp_detached, when it is not set (B_FALSE) indicates
2430                  * that the accept() has completed.
2431                  *
2432                  * Nor can it reassemble urgent pointers, so discard
2433                  * if it's not the next segment expected.
2434                  *
2435                  * Otherwise, collapse chain into one mblk (discard if
2436                  * that fails).  This makes sure the headers, retransmitted
2437                  * data, and new data all are in the same mblk.
2438                  */
2439                 ASSERT(mp != NULL);
2440                 if (tcp->tcp_detached || !pullupmsg(mp, -1)) {
2441                         freemsg(mp);
2442                         return;
2443                 }
2444                 /* Update pointers into message */
2445                 iphdr = rptr = mp->b_rptr;
2446                 tcpha = (tcpha_t *)&rptr[ip_hdr_len];
2447                 if (SEQ_GT(seg_seq, tcp->tcp_rnxt)) {
2448                         /*
2449                          * Since we can't handle any data with this urgent
2450                          * pointer that is out of sequence, we expunge
2451                          * the data.  This allows us to still register
2452                          * the urgent mark and generate the M_PCSIG,
2453                          * which we can do.
2454                          */
2455                         mp->b_wptr = (uchar_t *)tcpha + TCP_HDR_LENGTH(tcpha);
2456                         seg_len = 0;
2457                 }
2458         }
2459 
2460         sockupcalls = connp->conn_upcalls;
2461         /* A conn_t may have belonged to a now-closed socket.  Be careful. */
2462         if (sockupcalls == NULL)
2463                 sockupcalls = &tcp_dummy_upcalls;
2464 
2465         switch (tcp->tcp_state) {
2466         case TCPS_SYN_SENT:
2467                 if (connp->conn_final_sqp == NULL &&
2468                     tcp_outbound_squeue_switch && sqp != NULL) {
2469                         ASSERT(connp->conn_initial_sqp == connp->conn_sqp);
2470                         connp->conn_final_sqp = sqp;
2471                         if (connp->conn_final_sqp != connp->conn_sqp) {
2472                                 DTRACE_PROBE1(conn__final__sqp__switch,
2473                                     conn_t *, connp);
2474                                 CONN_INC_REF(connp);
2475                                 SQUEUE_SWITCH(connp, connp->conn_final_sqp);
2476                                 SQUEUE_ENTER_ONE(connp->conn_sqp, mp,
2477                                     tcp_input_data, connp, ira, ip_squeue_flag,
2478                                     SQTAG_CONNECT_FINISH);
2479                                 return;
2480                         }
2481                         DTRACE_PROBE1(conn__final__sqp__same, conn_t *, connp);
2482                 }
2483                 if (flags & TH_ACK) {
2484                         /*
2485                          * Note that our stack cannot send data before a
2486                          * connection is established, therefore the
2487                          * following check is valid.  Otherwise, it has
2488                          * to be changed.
2489                          */
2490                         if (SEQ_LEQ(seg_ack, tcp->tcp_iss) ||
2491                             SEQ_GT(seg_ack, tcp->tcp_snxt)) {
2492                                 freemsg(mp);
2493                                 if (flags & TH_RST)
2494                                         return;
2495                                 tcp_xmit_ctl("TCPS_SYN_SENT-Bad_seq",
2496                                     tcp, seg_ack, 0, TH_RST);
2497                                 return;
2498                         }
2499                         ASSERT(tcp->tcp_suna + 1 == seg_ack);
2500                 }
2501                 if (flags & TH_RST) {
2502                         if (flags & TH_ACK) {
2503                                 DTRACE_TCP5(connect__refused, mblk_t *, NULL,
2504                                     ip_xmit_attr_t *, connp->conn_ixa,
2505                                     void_ip_t *, iphdr, tcp_t *, tcp,
2506                                     tcph_t *, tcpha);
2507                                 (void) tcp_clean_death(tcp, ECONNREFUSED);
2508                         }
2509                         freemsg(mp);
2510                         return;
2511                 }
2512                 if (!(flags & TH_SYN)) {
2513                         freemsg(mp);
2514                         return;
2515                 }
2516 
2517                 /* Process all TCP options. */
2518                 tcp_process_options(tcp, tcpha);
2519                 /*
2520                  * The following changes our rwnd to be a multiple of the
2521                  * MIN(peer MSS, our MSS) for performance reason.
2522                  */
2523                 (void) tcp_rwnd_set(tcp, MSS_ROUNDUP(connp->conn_rcvbuf,
2524                     tcp->tcp_mss));
2525 
2526                 /* Is the other end ECN capable? */
2527                 if (tcp->tcp_ecn_ok) {
2528                         if ((flags & (TH_ECE|TH_CWR)) != TH_ECE) {
2529                                 tcp->tcp_ecn_ok = B_FALSE;
2530                         }
2531                 }
2532                 /*
2533                  * Clear ECN flags because it may interfere with later
2534                  * processing.
2535                  */
2536                 flags &= ~(TH_ECE|TH_CWR);
2537 
2538                 tcp->tcp_irs = seg_seq;
2539                 tcp->tcp_rack = seg_seq;
2540                 tcp->tcp_rnxt = seg_seq + 1;
2541                 tcp->tcp_tcpha->tha_ack = htonl(tcp->tcp_rnxt);
2542                 if (!TCP_IS_DETACHED(tcp)) {
2543                         /* Allocate room for SACK options if needed. */
2544                         connp->conn_wroff = connp->conn_ht_iphc_len;
2545                         if (tcp->tcp_snd_sack_ok)
2546                                 connp->conn_wroff += TCPOPT_MAX_SACK_LEN;
2547                         if (!tcp->tcp_loopback)
2548                                 connp->conn_wroff += tcps->tcps_wroff_xtra;
2549 
2550                         (void) proto_set_tx_wroff(connp->conn_rq, connp,
2551                             connp->conn_wroff);
2552                 }
2553                 if (flags & TH_ACK) {
2554                         /*
2555                          * If we can't get the confirmation upstream, pretend
2556                          * we didn't even see this one.
2557                          *
2558                          * XXX: how can we pretend we didn't see it if we
2559                          * have updated rnxt et. al.
2560                          *
2561                          * For loopback we defer sending up the T_CONN_CON
2562                          * until after some checks below.
2563                          */
2564                         mp1 = NULL;
2565                         /*
2566                          * tcp_sendmsg() checks tcp_state without entering
2567                          * the squeue so tcp_state should be updated before
2568                          * sending up connection confirmation.  Probe the
2569                          * state change below when we are sure the connection
2570                          * confirmation has been sent.
2571                          */
2572                         tcp->tcp_state = TCPS_ESTABLISHED;
2573                         if (!tcp_conn_con(tcp, iphdr, mp,
2574                             tcp->tcp_loopback ? &mp1 : NULL, ira)) {
2575                                 tcp->tcp_state = TCPS_SYN_SENT;
2576                                 freemsg(mp);
2577                                 return;
2578                         }
2579                         TCPS_CONN_INC(tcps);
2580                         /* SYN was acked - making progress */
2581                         tcp->tcp_ip_forward_progress = B_TRUE;
2582 
2583                         /* One for the SYN */
2584                         tcp->tcp_suna = tcp->tcp_iss + 1;
2585                         tcp->tcp_valid_bits &= ~TCP_ISS_VALID;
2586 
2587                         /*
2588                          * If SYN was retransmitted, need to reset all
2589                          * retransmission info.  This is because this
2590                          * segment will be treated as a dup ACK.
2591                          */
2592                         if (tcp->tcp_rexmit) {
2593                                 tcp->tcp_rexmit = B_FALSE;
2594                                 tcp->tcp_rexmit_nxt = tcp->tcp_snxt;
2595                                 tcp->tcp_rexmit_max = tcp->tcp_snxt;
2596                                 tcp->tcp_ms_we_have_waited = 0;
2597 
2598                                 /*
2599                                  * Set tcp_cwnd back to 1 MSS, per
2600                                  * recommendation from
2601                                  * draft-floyd-incr-init-win-01.txt,
2602                                  * Increasing TCP's Initial Window.
2603                                  */
2604                                 tcp->tcp_cwnd = tcp->tcp_mss;
2605                         }
2606 
2607                         tcp->tcp_swl1 = seg_seq;
2608                         tcp->tcp_swl2 = seg_ack;
2609 
2610                         new_swnd = ntohs(tcpha->tha_win);
2611                         tcp->tcp_swnd = new_swnd;
2612                         if (new_swnd > tcp->tcp_max_swnd)
2613                                 tcp->tcp_max_swnd = new_swnd;
2614 
2615                         /*
2616                          * Always send the three-way handshake ack immediately
2617                          * in order to make the connection complete as soon as
2618                          * possible on the accepting host.
2619                          */
2620                         flags |= TH_ACK_NEEDED;
2621 
2622                         /*
2623                          * Trace connect-established here.
2624                          */
2625                         DTRACE_TCP5(connect__established, mblk_t *, NULL,
2626                             ip_xmit_attr_t *, tcp->tcp_connp->conn_ixa,
2627                             void_ip_t *, iphdr, tcp_t *, tcp, tcph_t *, tcpha);
2628 
2629                         /* Trace change from SYN_SENT -> ESTABLISHED here */
2630                         DTRACE_TCP6(state__change, void, NULL, ip_xmit_attr_t *,
2631                             connp->conn_ixa, void, NULL, tcp_t *, tcp,
2632                             void, NULL, int32_t, TCPS_SYN_SENT);
2633 
2634                         /*
2635                          * Special case for loopback.  At this point we have
2636                          * received SYN-ACK from the remote endpoint.  In
2637                          * order to ensure that both endpoints reach the
2638                          * fused state prior to any data exchange, the final
2639                          * ACK needs to be sent before we indicate T_CONN_CON
2640                          * to the module upstream.
2641                          */
2642                         if (tcp->tcp_loopback) {
2643                                 mblk_t *ack_mp;
2644 
2645                                 ASSERT(!tcp->tcp_unfusable);
2646                                 ASSERT(mp1 != NULL);
2647                                 /*
2648                                  * For loopback, we always get a pure SYN-ACK
2649                                  * and only need to send back the final ACK
2650                                  * with no data (this is because the other
2651                                  * tcp is ours and we don't do T/TCP).  This
2652                                  * final ACK triggers the passive side to
2653                                  * perform fusion in ESTABLISHED state.
2654                                  */
2655                                 if ((ack_mp = tcp_ack_mp(tcp)) != NULL) {
2656                                         if (tcp->tcp_ack_tid != 0) {
2657                                                 (void) TCP_TIMER_CANCEL(tcp,
2658                                                     tcp->tcp_ack_tid);
2659                                                 tcp->tcp_ack_tid = 0;
2660                                         }
2661                                         tcp_send_data(tcp, ack_mp);
2662                                         BUMP_LOCAL(tcp->tcp_obsegs);
2663                                         TCPS_BUMP_MIB(tcps, tcpOutAck);
2664 
2665                                         if (!IPCL_IS_NONSTR(connp)) {
2666                                                 /* Send up T_CONN_CON */
2667                                                 if (ira->ira_cred != NULL) {
2668                                                         mblk_setcred(mp1,
2669                                                             ira->ira_cred,
2670                                                             ira->ira_cpid);
2671                                                 }
2672                                                 putnext(connp->conn_rq, mp1);
2673                                         } else {
2674                                                 (*sockupcalls->su_connected)
2675                                                     (connp->conn_upper_handle,
2676                                                     tcp->tcp_connid,
2677                                                     ira->ira_cred,
2678                                                     ira->ira_cpid);
2679                                                 freemsg(mp1);
2680                                         }
2681 
2682                                         freemsg(mp);
2683                                         return;
2684                                 }
2685                                 /*
2686                                  * Forget fusion; we need to handle more
2687                                  * complex cases below.  Send the deferred
2688                                  * T_CONN_CON message upstream and proceed
2689                                  * as usual.  Mark this tcp as not capable
2690                                  * of fusion.
2691                                  */
2692                                 TCP_STAT(tcps, tcp_fusion_unfusable);
2693                                 tcp->tcp_unfusable = B_TRUE;
2694                                 if (!IPCL_IS_NONSTR(connp)) {
2695                                         if (ira->ira_cred != NULL) {
2696                                                 mblk_setcred(mp1, ira->ira_cred,
2697                                                     ira->ira_cpid);
2698                                         }
2699                                         putnext(connp->conn_rq, mp1);
2700                                 } else {
2701                                         (*sockupcalls->su_connected)
2702                                             (connp->conn_upper_handle,
2703                                             tcp->tcp_connid, ira->ira_cred,
2704                                             ira->ira_cpid);
2705                                         freemsg(mp1);
2706                                 }
2707                         }
2708 
2709                         /*
2710                          * Check to see if there is data to be sent.  If
2711                          * yes, set the transmit flag.  Then check to see
2712                          * if received data processing needs to be done.
2713                          * If not, go straight to xmit_check.  This short
2714                          * cut is OK as we don't support T/TCP.
2715                          */
2716                         if (tcp->tcp_unsent)
2717                                 flags |= TH_XMIT_NEEDED;
2718 
2719                         if (seg_len == 0 && !(flags & TH_URG)) {
2720                                 freemsg(mp);
2721                                 goto xmit_check;
2722                         }
2723 
2724                         flags &= ~TH_SYN;
2725                         seg_seq++;
2726                         break;
2727                 }
2728                 tcp->tcp_state = TCPS_SYN_RCVD;
2729                 DTRACE_TCP6(state__change, void, NULL, ip_xmit_attr_t *,
2730                     connp->conn_ixa, void_ip_t *, NULL, tcp_t *, tcp,
2731                     tcph_t *, NULL, int32_t, TCPS_SYN_SENT);
2732                 mp1 = tcp_xmit_mp(tcp, tcp->tcp_xmit_head, tcp->tcp_mss,
2733                     NULL, NULL, tcp->tcp_iss, B_FALSE, NULL, B_FALSE);
2734                 if (mp1 != NULL) {
2735                         tcp_send_data(tcp, mp1);
2736                         TCP_TIMER_RESTART(tcp, tcp->tcp_rto);
2737                 }
2738                 freemsg(mp);
2739                 return;
2740         case TCPS_SYN_RCVD:
2741                 if (flags & TH_ACK) {
2742                         uint32_t pinit_wnd;
2743 
2744                         /*
2745                          * In this state, a SYN|ACK packet is either bogus
2746                          * because the other side must be ACKing our SYN which
2747                          * indicates it has seen the ACK for their SYN and
2748                          * shouldn't retransmit it or we're crossing SYNs
2749                          * on active open.
2750                          */
2751                         if ((flags & TH_SYN) && !tcp->tcp_active_open) {
2752                                 freemsg(mp);
2753                                 tcp_xmit_ctl("TCPS_SYN_RCVD-bad_syn",
2754                                     tcp, seg_ack, 0, TH_RST);
2755                                 return;
2756                         }
2757                         /*
2758                          * NOTE: RFC 793 pg. 72 says this should be
2759                          * tcp->tcp_suna <= seg_ack <= tcp->tcp_snxt
2760                          * but that would mean we have an ack that ignored
2761                          * our SYN.
2762                          */
2763                         if (SEQ_LEQ(seg_ack, tcp->tcp_suna) ||
2764                             SEQ_GT(seg_ack, tcp->tcp_snxt)) {
2765                                 freemsg(mp);
2766                                 tcp_xmit_ctl("TCPS_SYN_RCVD-bad_ack",
2767                                     tcp, seg_ack, 0, TH_RST);
2768                                 return;
2769                         }
2770                         /*
2771                          * No sane TCP stack will send such a small window
2772                          * without receiving any data.  Just drop this invalid
2773                          * ACK.  We also shorten the abort timeout in case
2774                          * this is an attack.
2775                          */
2776                         pinit_wnd = ntohs(tcpha->tha_win) << tcp->tcp_snd_ws;
2777                         if (pinit_wnd < tcp->tcp_mss &&
2778                             pinit_wnd < tcp_init_wnd_chk) {
2779                                 freemsg(mp);
2780                                 TCP_STAT(tcps, tcp_zwin_ack_syn);
2781                                 tcp->tcp_second_ctimer_threshold =
2782                                     tcp_early_abort * SECONDS;
2783                                 return;
2784                         }
2785                 }
2786                 break;
2787         case TCPS_LISTEN:
2788                 /*
2789                  * Only a TLI listener can come through this path when a
2790                  * acceptor is going back to be a listener and a packet
2791                  * for the acceptor hits the classifier. For a socket
2792                  * listener, this can never happen because a listener
2793                  * can never accept connection on itself and hence a
2794                  * socket acceptor can not go back to being a listener.
2795                  */
2796                 ASSERT(!TCP_IS_SOCKET(tcp));
2797                 /*FALLTHRU*/
2798         case TCPS_CLOSED:
2799         case TCPS_BOUND: {
2800                 conn_t  *new_connp;
2801                 ip_stack_t *ipst = tcps->tcps_netstack->netstack_ip;
2802 
2803                 /*
2804                  * Don't accept any input on a closed tcp as this TCP logically
2805                  * does not exist on the system. Don't proceed further with
2806                  * this TCP. For instance, this packet could trigger another
2807                  * close of this tcp which would be disastrous for tcp_refcnt.
2808                  * tcp_close_detached / tcp_clean_death / tcp_closei_local must
2809                  * be called at most once on a TCP. In this case we need to
2810                  * refeed the packet into the classifier and figure out where
2811                  * the packet should go.
2812                  */
2813                 new_connp = ipcl_classify(mp, ira, ipst);
2814                 if (new_connp != NULL) {
2815                         /* Drops ref on new_connp */
2816                         tcp_reinput(new_connp, mp, ira, ipst);
2817                         return;
2818                 }
2819                 /* We failed to classify. For now just drop the packet */
2820                 freemsg(mp);
2821                 return;
2822         }
2823         case TCPS_IDLE:
2824                 /*
2825                  * Handle the case where the tcp_clean_death() has happened
2826                  * on a connection (application hasn't closed yet) but a packet
2827                  * was already queued on squeue before tcp_clean_death()
2828                  * was processed. Calling tcp_clean_death() twice on same
2829                  * connection can result in weird behaviour.
2830                  */
2831                 freemsg(mp);
2832                 return;
2833         default:
2834                 break;
2835         }
2836 
2837         /*
2838          * Already on the correct queue/perimeter.
2839          * If this is a detached connection and not an eager
2840          * connection hanging off a listener then new data
2841          * (past the FIN) will cause a reset.
2842          * We do a special check here where it
2843          * is out of the main line, rather than check
2844          * if we are detached every time we see new
2845          * data down below.
2846          */
2847         if (TCP_IS_DETACHED_NONEAGER(tcp) &&
2848             (seg_len > 0 && SEQ_GT(seg_seq + seg_len, tcp->tcp_rnxt))) {
2849                 TCPS_BUMP_MIB(tcps, tcpInClosed);
2850                 DTRACE_PROBE2(tcp__trace__recv, mblk_t *, mp, tcp_t *, tcp);
2851                 freemsg(mp);
2852                 tcp_xmit_ctl("new data when detached", tcp,
2853                     tcp->tcp_snxt, 0, TH_RST);
2854                 (void) tcp_clean_death(tcp, EPROTO);
2855                 return;
2856         }
2857 
2858         mp->b_rptr = (uchar_t *)tcpha + TCP_HDR_LENGTH(tcpha);
2859         urp = ntohs(tcpha->tha_urp) - TCP_OLD_URP_INTERPRETATION;
2860         new_swnd = ntohs(tcpha->tha_win) <<
2861             ((tcpha->tha_flags & TH_SYN) ? 0 : tcp->tcp_snd_ws);
2862 
2863         /*
2864          * We are interested in two TCP options: timestamps (if negotiated) and
2865          * SACK (if negotiated). Skip option parsing if neither is negotiated.
2866          */
2867         if (tcp->tcp_snd_ts_ok || tcp->tcp_snd_sack_ok) {
2868                 int options;
2869                 if (tcp->tcp_snd_sack_ok)
2870                         tcpopt.tcp = tcp;
2871                 else
2872                         tcpopt.tcp = NULL;
2873                 options = tcp_parse_options(tcpha, &tcpopt);
2874                 /*
2875                  * RST segments must not be subject to PAWS and are not
2876                  * required to have timestamps.
2877                  * We do not drop keepalive segments without
2878                  * timestamps, to maintain compatibility with legacy TCP stacks.
2879                  */
2880                 boolean_t keepalive = (seg_len == 0 || seg_len == 1) &&
2881                     (seg_seq + 1 == tcp->tcp_rnxt);
2882                 if (tcp->tcp_snd_ts_ok && !(flags & TH_RST) && !keepalive) {
2883                         /*
2884                          * Per RFC 7323 section 3.2., silently drop non-RST
2885                          * segments without expected TSopt. This is a 'SHOULD'
2886                          * requirement.
2887                          * We accept keepalives without TSopt to maintain
2888                          * interoperability with tcp implementations that omit
2889                          * the TSopt on these. Keepalive data is discarded, so
2890                          * there is no risk corrupting data by accepting these.
2891                          */
2892                         if (!(options & TCP_OPT_TSTAMP_PRESENT)) {
2893                                 /*
2894                                  * Leave a breadcrumb for people to detect this
2895                                  * behavior.
2896                                  */
2897                                 DTRACE_TCP1(droppedtimestamp, tcp_t *, tcp);
2898                                 freemsg(mp);
2899                                 return;
2900                         }
2901 
2902                         if (!tcp_paws_check(tcp, &tcpopt)) {
2903                                 /*
2904                                  * This segment is not acceptable.
2905                                  * Drop it and send back an ACK.
2906                                  */
2907                                 freemsg(mp);
2908                                 flags |= TH_ACK_NEEDED;
2909                                 goto ack_check;
2910                         }
2911                 }
2912         }
2913 try_again:;
2914         mss = tcp->tcp_mss;
2915         gap = seg_seq - tcp->tcp_rnxt;
2916         rgap = tcp->tcp_rwnd - (gap + seg_len);
2917         /*
2918          * gap is the amount of sequence space between what we expect to see
2919          * and what we got for seg_seq.  A positive value for gap means
2920          * something got lost.  A negative value means we got some old stuff.
2921          */
2922         if (gap < 0) {
2923                 /* Old stuff present.  Is the SYN in there? */
2924                 if (seg_seq == tcp->tcp_irs && (flags & TH_SYN) &&
2925                     (seg_len != 0)) {
2926                         flags &= ~TH_SYN;
2927                         seg_seq++;
2928                         urp--;
2929                         /* Recompute the gaps after noting the SYN. */
2930                         goto try_again;
2931                 }
2932                 TCPS_BUMP_MIB(tcps, tcpInDataDupSegs);
2933                 TCPS_UPDATE_MIB(tcps, tcpInDataDupBytes,
2934                     (seg_len > -gap ? -gap : seg_len));
2935                 /* Remove the old stuff from seg_len. */
2936                 seg_len += gap;
2937                 /*
2938                  * Anything left?
2939                  * Make sure to check for unack'd FIN when rest of data
2940                  * has been previously ack'd.
2941                  */
2942                 if (seg_len < 0 || (seg_len == 0 && !(flags & TH_FIN))) {
2943                         /*
2944                          * Resets are only valid if they lie within our offered
2945                          * window.  If the RST bit is set, we just ignore this
2946                          * segment.
2947                          */
2948                         if (flags & TH_RST) {
2949                                 freemsg(mp);
2950                                 return;
2951                         }
2952 
2953                         /*
2954                          * The arriving of dup data packets indicate that we
2955                          * may have postponed an ack for too long, or the other
2956                          * side's RTT estimate is out of shape. Start acking
2957                          * more often.
2958                          */
2959                         if (SEQ_GEQ(seg_seq + seg_len - gap, tcp->tcp_rack) &&
2960                             tcp->tcp_rack_cnt >= 1 &&
2961                             tcp->tcp_rack_abs_max > 2) {
2962                                 tcp->tcp_rack_abs_max--;
2963                         }
2964                         tcp->tcp_rack_cur_max = 1;
2965 
2966                         /*
2967                          * This segment is "unacceptable".  None of its
2968                          * sequence space lies within our advertized window.
2969                          *
2970                          * Adjust seg_len to the original value for tracing.
2971                          */
2972                         seg_len -= gap;
2973                         if (connp->conn_debug) {
2974                                 (void) strlog(TCP_MOD_ID, 0, 1, SL_TRACE,
2975                                     "tcp_rput: unacceptable, gap %d, rgap %d, "
2976                                     "flags 0x%x, seg_seq %u, seg_ack %u, "
2977                                     "seg_len %d, rnxt %u, snxt %u, %s",
2978                                     gap, rgap, flags, seg_seq, seg_ack,
2979                                     seg_len, tcp->tcp_rnxt, tcp->tcp_snxt,
2980                                     tcp_display(tcp, NULL,
2981                                     DISP_ADDR_AND_PORT));
2982                         }
2983 
2984                         /*
2985                          * Arrange to send an ACK in response to the
2986                          * unacceptable segment per RFC 793 page 69. There
2987                          * is only one small difference between ours and the
2988                          * acceptability test in the RFC - we accept ACK-only
2989                          * packet with SEG.SEQ = RCV.NXT+RCV.WND and no ACK
2990                          * will be generated.
2991                          *
2992                          * Note that we have to ACK an ACK-only packet at least
2993                          * for stacks that send 0-length keep-alives with
2994                          * SEG.SEQ = SND.NXT-1 as recommended by RFC1122,
2995                          * section 4.2.3.6. As long as we don't ever generate
2996                          * an unacceptable packet in response to an incoming
2997                          * packet that is unacceptable, it should not cause
2998                          * "ACK wars".
2999                          */
3000                         flags |=  TH_ACK_NEEDED;
3001 
3002                         /*
3003                          * Continue processing this segment in order to use the
3004                          * ACK information it contains, but skip all other
3005                          * sequence-number processing.  Processing the ACK
3006                          * information is necessary in order to
3007                          * re-synchronize connections that may have lost
3008                          * synchronization.
3009                          *
3010                          * We clear seg_len and flag fields related to
3011                          * sequence number processing as they are not
3012                          * to be trusted for an unacceptable segment.
3013                          */
3014                         seg_len = 0;
3015                         flags &= ~(TH_SYN | TH_FIN | TH_URG);
3016                         goto process_ack;
3017                 }
3018 
3019                 /* Fix seg_seq, and chew the gap off the front. */
3020                 seg_seq = tcp->tcp_rnxt;
3021                 urp += gap;
3022                 do {
3023                         mblk_t  *mp2;
3024                         ASSERT((uintptr_t)(mp->b_wptr - mp->b_rptr) <=
3025                             (uintptr_t)UINT_MAX);
3026                         gap += (uint_t)(mp->b_wptr - mp->b_rptr);
3027                         if (gap > 0) {
3028                                 mp->b_rptr = mp->b_wptr - gap;
3029                                 break;
3030                         }
3031                         mp2 = mp;
3032                         mp = mp->b_cont;
3033                         freeb(mp2);
3034                 } while (gap < 0);
3035                 /*
3036                  * If the urgent data has already been acknowledged, we
3037                  * should ignore TH_URG below
3038                  */
3039                 if (urp < 0)
3040                         flags &= ~TH_URG;
3041         }
3042         /*
3043          * rgap is the amount of stuff received out of window.  A negative
3044          * value is the amount out of window.
3045          */
3046         if (rgap < 0) {
3047                 mblk_t  *mp2;
3048 
3049                 if (tcp->tcp_rwnd == 0) {
3050                         TCPS_BUMP_MIB(tcps, tcpInWinProbe);
3051                 } else {
3052                         TCPS_BUMP_MIB(tcps, tcpInDataPastWinSegs);
3053                         TCPS_UPDATE_MIB(tcps, tcpInDataPastWinBytes, -rgap);
3054                 }
3055 
3056                 /*
3057                  * seg_len does not include the FIN, so if more than
3058                  * just the FIN is out of window, we act like we don't
3059                  * see it.  (If just the FIN is out of window, rgap
3060                  * will be zero and we will go ahead and acknowledge
3061                  * the FIN.)
3062                  */
3063                 flags &= ~TH_FIN;
3064 
3065                 /* Fix seg_len and make sure there is something left. */
3066                 seg_len += rgap;
3067                 if (seg_len <= 0) {
3068                         /*
3069                          * Resets are only valid if they lie within our offered
3070                          * window.  If the RST bit is set, we just ignore this
3071                          * segment.
3072                          */
3073                         if (flags & TH_RST) {
3074                                 freemsg(mp);
3075                                 return;
3076                         }
3077 
3078                         /* Per RFC 793, we need to send back an ACK. */
3079                         flags |= TH_ACK_NEEDED;
3080 
3081                         /*
3082                          * Send SIGURG as soon as possible i.e. even
3083                          * if the TH_URG was delivered in a window probe
3084                          * packet (which will be unacceptable).
3085                          *
3086                          * We generate a signal if none has been generated
3087                          * for this connection or if this is a new urgent
3088                          * byte. Also send a zero-length "unmarked" message
3089                          * to inform SIOCATMARK that this is not the mark.
3090                          *
3091                          * tcp_urp_last_valid is cleared when the T_exdata_ind
3092                          * is sent up. This plus the check for old data
3093                          * (gap >= 0) handles the wraparound of the sequence
3094                          * number space without having to always track the
3095                          * correct MAX(tcp_urp_last, tcp_rnxt). (BSD tracks
3096                          * this max in its rcv_up variable).
3097                          *
3098                          * This prevents duplicate SIGURGS due to a "late"
3099                          * zero-window probe when the T_EXDATA_IND has already
3100                          * been sent up.
3101                          */
3102                         if ((flags & TH_URG) &&
3103                             (!tcp->tcp_urp_last_valid || SEQ_GT(urp + seg_seq,
3104                             tcp->tcp_urp_last))) {
3105                                 if (IPCL_IS_NONSTR(connp)) {
3106                                         if (!TCP_IS_DETACHED(tcp)) {
3107                                                 (*sockupcalls->su_signal_oob)
3108                                                     (connp->conn_upper_handle,
3109                                                     urp);
3110                                         }
3111                                 } else {
3112                                         mp1 = allocb(0, BPRI_MED);
3113                                         if (mp1 == NULL) {
3114                                                 freemsg(mp);
3115                                                 return;
3116                                         }
3117                                         if (!TCP_IS_DETACHED(tcp) &&
3118                                             !putnextctl1(connp->conn_rq,
3119                                             M_PCSIG, SIGURG)) {
3120                                                 /* Try again on the rexmit. */
3121                                                 freemsg(mp1);
3122                                                 freemsg(mp);
3123                                                 return;
3124                                         }
3125                                         /*
3126                                          * If the next byte would be the mark
3127                                          * then mark with MARKNEXT else mark
3128                                          * with NOTMARKNEXT.
3129                                          */
3130                                         if (gap == 0 && urp == 0)
3131                                                 mp1->b_flag |= MSGMARKNEXT;
3132                                         else
3133                                                 mp1->b_flag |= MSGNOTMARKNEXT;
3134                                         freemsg(tcp->tcp_urp_mark_mp);
3135                                         tcp->tcp_urp_mark_mp = mp1;
3136                                         flags |= TH_SEND_URP_MARK;
3137                                 }
3138                                 tcp->tcp_urp_last_valid = B_TRUE;
3139                                 tcp->tcp_urp_last = urp + seg_seq;
3140                         }
3141                         /*
3142                          * If this is a zero window probe, continue to
3143                          * process the ACK part.  But we need to set seg_len
3144                          * to 0 to avoid data processing.  Otherwise just
3145                          * drop the segment and send back an ACK.
3146                          */
3147                         if (tcp->tcp_rwnd == 0 && seg_seq == tcp->tcp_rnxt) {
3148                                 flags &= ~(TH_SYN | TH_URG);
3149                                 seg_len = 0;
3150                                 goto process_ack;
3151                         } else {
3152                                 freemsg(mp);
3153                                 goto ack_check;
3154                         }
3155                 }
3156                 /* Pitch out of window stuff off the end. */
3157                 rgap = seg_len;
3158                 mp2 = mp;
3159                 do {
3160                         ASSERT((uintptr_t)(mp2->b_wptr - mp2->b_rptr) <=
3161                             (uintptr_t)INT_MAX);
3162                         rgap -= (int)(mp2->b_wptr - mp2->b_rptr);
3163                         if (rgap < 0) {
3164                                 mp2->b_wptr += rgap;
3165                                 if ((mp1 = mp2->b_cont) != NULL) {
3166                                         mp2->b_cont = NULL;
3167                                         freemsg(mp1);
3168                                 }
3169                                 break;
3170                         }
3171                 } while ((mp2 = mp2->b_cont) != NULL);
3172         }
3173 ok:;
3174         /*
3175          * TCP should check ECN info for segments inside the window only.
3176          * Therefore the check should be done here.
3177          */
3178         if (tcp->tcp_ecn_ok) {
3179                 if (flags & TH_CWR) {
3180                         tcp->tcp_ecn_echo_on = B_FALSE;
3181                 }
3182                 /*
3183                  * Note that both ECN_CE and CWR can be set in the
3184                  * same segment.  In this case, we once again turn
3185                  * on ECN_ECHO.
3186                  */
3187                 if (connp->conn_ipversion == IPV4_VERSION) {
3188                         uchar_t tos = ((ipha_t *)rptr)->ipha_type_of_service;
3189 
3190                         if ((tos & IPH_ECN_CE) == IPH_ECN_CE) {
3191                                 tcp->tcp_ecn_echo_on = B_TRUE;
3192                         }
3193                 } else {
3194                         uint32_t vcf = ((ip6_t *)rptr)->ip6_vcf;
3195 
3196                         if ((vcf & htonl(IPH_ECN_CE << 20)) ==
3197                             htonl(IPH_ECN_CE << 20)) {
3198                                 tcp->tcp_ecn_echo_on = B_TRUE;
3199                         }
3200                 }
3201         }
3202 
3203         /*
3204          * Check whether we can update tcp_ts_recent. This test is from RFC
3205          * 7323, section 5.3.
3206          */
3207         if (tcp->tcp_snd_ts_ok && !(flags & TH_RST) &&
3208             TSTMP_GEQ(tcpopt.tcp_opt_ts_val, tcp->tcp_ts_recent) &&
3209             SEQ_LEQ(seg_seq, tcp->tcp_rack)) {
3210                 tcp->tcp_ts_recent = tcpopt.tcp_opt_ts_val;
3211                 tcp->tcp_last_rcv_lbolt = LBOLT_FASTPATH64;
3212         }
3213 
3214         if (seg_seq != tcp->tcp_rnxt || tcp->tcp_reass_head) {
3215                 /*
3216                  * FIN in an out of order segment.  We record this in
3217                  * tcp_valid_bits and the seq num of FIN in tcp_ofo_fin_seq.
3218                  * Clear the FIN so that any check on FIN flag will fail.
3219                  * Remember that FIN also counts in the sequence number
3220                  * space.  So we need to ack out of order FIN only segments.
3221                  */
3222                 if (flags & TH_FIN) {
3223                         tcp->tcp_valid_bits |= TCP_OFO_FIN_VALID;
3224                         tcp->tcp_ofo_fin_seq = seg_seq + seg_len;
3225                         flags &= ~TH_FIN;
3226                         flags |= TH_ACK_NEEDED;
3227                 }
3228                 if (seg_len > 0) {
3229                         /* Fill in the SACK blk list. */
3230                         if (tcp->tcp_snd_sack_ok) {
3231                                 tcp_sack_insert(tcp->tcp_sack_list,
3232                                     seg_seq, seg_seq + seg_len,
3233                                     &(tcp->tcp_num_sack_blk));
3234                         }
3235 
3236                         /*
3237                          * Attempt reassembly and see if we have something
3238                          * ready to go.
3239                          */
3240                         mp = tcp_reass(tcp, mp, seg_seq);
3241                         /* Always ack out of order packets */
3242                         flags |= TH_ACK_NEEDED | TH_PUSH;
3243                         if (mp) {
3244                                 ASSERT((uintptr_t)(mp->b_wptr - mp->b_rptr) <=
3245                                     (uintptr_t)INT_MAX);
3246                                 seg_len = mp->b_cont ? msgdsize(mp) :
3247                                     (int)(mp->b_wptr - mp->b_rptr);
3248                                 seg_seq = tcp->tcp_rnxt;
3249                                 /*
3250                                  * A gap is filled and the seq num and len
3251                                  * of the gap match that of a previously
3252                                  * received FIN, put the FIN flag back in.
3253                                  */
3254                                 if ((tcp->tcp_valid_bits & TCP_OFO_FIN_VALID) &&
3255                                     seg_seq + seg_len == tcp->tcp_ofo_fin_seq) {
3256                                         flags |= TH_FIN;
3257                                         tcp->tcp_valid_bits &=
3258                                             ~TCP_OFO_FIN_VALID;
3259                                 }
3260                                 if (tcp->tcp_reass_tid != 0) {
3261                                         (void) TCP_TIMER_CANCEL(tcp,
3262                                             tcp->tcp_reass_tid);
3263                                         /*
3264                                          * Restart the timer if there is still
3265                                          * data in the reassembly queue.
3266                                          */
3267                                         if (tcp->tcp_reass_head != NULL) {
3268                                                 tcp->tcp_reass_tid = TCP_TIMER(
3269                                                     tcp, tcp_reass_timer,
3270                                                     tcps->tcps_reass_timeout);
3271                                         } else {
3272                                                 tcp->tcp_reass_tid = 0;
3273                                         }
3274                                 }
3275                         } else {
3276                                 /*
3277                                  * Keep going even with NULL mp.
3278                                  * There may be a useful ACK or something else
3279                                  * we don't want to miss.
3280                                  *
3281                                  * But TCP should not perform fast retransmit
3282                                  * because of the ack number.  TCP uses
3283                                  * seg_len == 0 to determine if it is a pure
3284                                  * ACK.  And this is not a pure ACK.
3285                                  */
3286                                 seg_len = 0;
3287                                 ofo_seg = B_TRUE;
3288 
3289                                 if (tcps->tcps_reass_timeout != 0 &&
3290                                     tcp->tcp_reass_tid == 0) {
3291                                         tcp->tcp_reass_tid = TCP_TIMER(tcp,
3292                                             tcp_reass_timer,
3293                                             tcps->tcps_reass_timeout);
3294                                 }
3295                         }
3296                 }
3297         } else if (seg_len > 0) {
3298                 TCPS_BUMP_MIB(tcps, tcpInDataInorderSegs);
3299                 TCPS_UPDATE_MIB(tcps, tcpInDataInorderBytes, seg_len);
3300                 /*
3301                  * If an out of order FIN was received before, and the seq
3302                  * num and len of the new segment match that of the FIN,
3303                  * put the FIN flag back in.
3304                  */
3305                 if ((tcp->tcp_valid_bits & TCP_OFO_FIN_VALID) &&
3306                     seg_seq + seg_len == tcp->tcp_ofo_fin_seq) {
3307                         flags |= TH_FIN;
3308                         tcp->tcp_valid_bits &= ~TCP_OFO_FIN_VALID;
3309                 }
3310         }
3311         if ((flags & (TH_RST | TH_SYN | TH_URG | TH_ACK)) != TH_ACK) {
3312         if (flags & TH_RST) {
3313                 freemsg(mp);
3314                 switch (tcp->tcp_state) {
3315                 case TCPS_SYN_RCVD:
3316                         (void) tcp_clean_death(tcp, ECONNREFUSED);
3317                         break;
3318                 case TCPS_ESTABLISHED:
3319                 case TCPS_FIN_WAIT_1:
3320                 case TCPS_FIN_WAIT_2:
3321                 case TCPS_CLOSE_WAIT:
3322                         (void) tcp_clean_death(tcp, ECONNRESET);
3323                         break;
3324                 case TCPS_CLOSING:
3325                 case TCPS_LAST_ACK:
3326                         (void) tcp_clean_death(tcp, 0);
3327                         break;
3328                 default:
3329                         ASSERT(tcp->tcp_state != TCPS_TIME_WAIT);
3330                         (void) tcp_clean_death(tcp, ENXIO);
3331                         break;
3332                 }
3333                 return;
3334         }
3335         if (flags & TH_SYN) {
3336                 /*
3337                  * See RFC 793, Page 71
3338                  *
3339                  * The seq number must be in the window as it should
3340                  * be "fixed" above.  If it is outside window, it should
3341                  * be already rejected.  Note that we allow seg_seq to be
3342                  * rnxt + rwnd because we want to accept 0 window probe.
3343                  */
3344                 ASSERT(SEQ_GEQ(seg_seq, tcp->tcp_rnxt) &&
3345                     SEQ_LEQ(seg_seq, tcp->tcp_rnxt + tcp->tcp_rwnd));
3346                 freemsg(mp);
3347                 /*
3348                  * If the ACK flag is not set, just use our snxt as the
3349                  * seq number of the RST segment.
3350                  */
3351                 if (!(flags & TH_ACK)) {
3352                         seg_ack = tcp->tcp_snxt;
3353                 }
3354                 tcp_xmit_ctl("TH_SYN", tcp, seg_ack, seg_seq + 1,
3355                     TH_RST|TH_ACK);
3356                 ASSERT(tcp->tcp_state != TCPS_TIME_WAIT);
3357                 (void) tcp_clean_death(tcp, ECONNRESET);
3358                 return;
3359         }
3360         /*
3361          * urp could be -1 when the urp field in the packet is 0
3362          * and TCP_OLD_URP_INTERPRETATION is set. This implies that the urgent
3363          * byte was at seg_seq - 1, in which case we ignore the urgent flag.
3364          */
3365         if (flags & TH_URG && urp >= 0) {
3366                 if (!tcp->tcp_urp_last_valid ||
3367                     SEQ_GT(urp + seg_seq, tcp->tcp_urp_last)) {
3368                         /*
3369                          * Non-STREAMS sockets handle the urgent data a litte
3370                          * differently from STREAMS based sockets. There is no
3371                          * need to mark any mblks with the MSG{NOT,}MARKNEXT
3372                          * flags to keep SIOCATMARK happy. Instead a
3373                          * su_signal_oob upcall is made to update the mark.
3374                          * Neither is a T_EXDATA_IND mblk needed to be
3375                          * prepended to the urgent data. The urgent data is
3376                          * delivered using the su_recv upcall, where we set
3377                          * the MSG_OOB flag to indicate that it is urg data.
3378                          *
3379                          * Neither TH_SEND_URP_MARK nor TH_MARKNEXT_NEEDED
3380                          * are used by non-STREAMS sockets.
3381                          */
3382                         if (IPCL_IS_NONSTR(connp)) {
3383                                 if (!TCP_IS_DETACHED(tcp)) {
3384                                         (*sockupcalls->su_signal_oob)
3385                                             (connp->conn_upper_handle, urp);
3386                                 }
3387                         } else {
3388                                 /*
3389                                  * If we haven't generated the signal yet for
3390                                  * this urgent pointer value, do it now.  Also,
3391                                  * send up a zero-length M_DATA indicating
3392                                  * whether or not this is the mark. The latter
3393                                  * is not needed when a T_EXDATA_IND is sent up.
3394                                  * However, if there are allocation failures
3395                                  * this code relies on the sender retransmitting
3396                                  * and the socket code for determining the mark
3397                                  * should not block waiting for the peer to
3398                                  * transmit. Thus, for simplicity we always
3399                                  * send up the mark indication.
3400                                  */
3401                                 mp1 = allocb(0, BPRI_MED);
3402                                 if (mp1 == NULL) {
3403                                         freemsg(mp);
3404                                         return;
3405                                 }
3406                                 if (!TCP_IS_DETACHED(tcp) &&
3407                                     !putnextctl1(connp->conn_rq, M_PCSIG,
3408                                     SIGURG)) {
3409                                         /* Try again on the rexmit. */
3410                                         freemsg(mp1);
3411                                         freemsg(mp);
3412                                         return;
3413                                 }
3414                                 /*
3415                                  * Mark with NOTMARKNEXT for now.
3416                                  * The code below will change this to MARKNEXT
3417                                  * if we are at the mark.
3418                                  *
3419                                  * If there are allocation failures (e.g. in
3420                                  * dupmsg below) the next time tcp_input_data
3421                                  * sees the urgent segment it will send up the
3422                                  * MSGMARKNEXT message.
3423                                  */
3424                                 mp1->b_flag |= MSGNOTMARKNEXT;
3425                                 freemsg(tcp->tcp_urp_mark_mp);
3426                                 tcp->tcp_urp_mark_mp = mp1;
3427                                 flags |= TH_SEND_URP_MARK;
3428 #ifdef DEBUG
3429                                 (void) strlog(TCP_MOD_ID, 0, 1, SL_TRACE,
3430                                     "tcp_rput: sent M_PCSIG 2 seq %x urp %x "
3431                                     "last %x, %s",
3432                                     seg_seq, urp, tcp->tcp_urp_last,
3433                                     tcp_display(tcp, NULL, DISP_PORT_ONLY));
3434 #endif /* DEBUG */
3435                         }
3436                         tcp->tcp_urp_last_valid = B_TRUE;
3437                         tcp->tcp_urp_last = urp + seg_seq;
3438                 } else if (tcp->tcp_urp_mark_mp != NULL) {
3439                         /*
3440                          * An allocation failure prevented the previous
3441                          * tcp_input_data from sending up the allocated
3442                          * MSG*MARKNEXT message - send it up this time
3443                          * around.
3444                          */
3445                         flags |= TH_SEND_URP_MARK;
3446                 }
3447 
3448                 /*
3449                  * If the urgent byte is in this segment, make sure that it is
3450                  * all by itself.  This makes it much easier to deal with the
3451                  * possibility of an allocation failure on the T_exdata_ind.
3452                  * Note that seg_len is the number of bytes in the segment, and
3453                  * urp is the offset into the segment of the urgent byte.
3454                  * urp < seg_len means that the urgent byte is in this segment.
3455                  */
3456                 if (urp < seg_len) {
3457                         if (seg_len != 1) {
3458                                 uint32_t  tmp_rnxt;
3459                                 /*
3460                                  * Break it up and feed it back in.
3461                                  * Re-attach the IP header.
3462                                  */
3463                                 mp->b_rptr = iphdr;
3464                                 if (urp > 0) {
3465                                         /*
3466                                          * There is stuff before the urgent
3467                                          * byte.
3468                                          */
3469                                         mp1 = dupmsg(mp);
3470                                         if (!mp1) {
3471                                                 /*
3472                                                  * Trim from urgent byte on.
3473                                                  * The rest will come back.
3474                                                  */
3475                                                 (void) adjmsg(mp,
3476                                                     urp - seg_len);
3477                                                 tcp_input_data(connp,
3478                                                     mp, NULL, ira);
3479                                                 return;
3480                                         }
3481                                         (void) adjmsg(mp1, urp - seg_len);
3482                                         /* Feed this piece back in. */
3483                                         tmp_rnxt = tcp->tcp_rnxt;
3484                                         tcp_input_data(connp, mp1, NULL, ira);
3485                                         /*
3486                                          * If the data passed back in was not
3487                                          * processed (ie: bad ACK) sending
3488                                          * the remainder back in will cause a
3489                                          * loop. In this case, drop the
3490                                          * packet and let the sender try
3491                                          * sending a good packet.
3492                                          */
3493                                         if (tmp_rnxt == tcp->tcp_rnxt) {
3494                                                 freemsg(mp);
3495                                                 return;
3496                                         }
3497                                 }
3498                                 if (urp != seg_len - 1) {
3499                                         uint32_t  tmp_rnxt;
3500                                         /*
3501                                          * There is stuff after the urgent
3502                                          * byte.
3503                                          */
3504                                         mp1 = dupmsg(mp);
3505                                         if (!mp1) {
3506                                                 /*
3507                                                  * Trim everything beyond the
3508                                                  * urgent byte.  The rest will
3509                                                  * come back.
3510                                                  */
3511                                                 (void) adjmsg(mp,
3512                                                     urp + 1 - seg_len);
3513                                                 tcp_input_data(connp,
3514                                                     mp, NULL, ira);
3515                                                 return;
3516                                         }
3517                                         (void) adjmsg(mp1, urp + 1 - seg_len);
3518                                         tmp_rnxt = tcp->tcp_rnxt;
3519                                         tcp_input_data(connp, mp1, NULL, ira);
3520                                         /*
3521                                          * If the data passed back in was not
3522                                          * processed (ie: bad ACK) sending
3523                                          * the remainder back in will cause a
3524                                          * loop. In this case, drop the
3525                                          * packet and let the sender try
3526                                          * sending a good packet.
3527                                          */
3528                                         if (tmp_rnxt == tcp->tcp_rnxt) {
3529                                                 freemsg(mp);
3530                                                 return;
3531                                         }
3532                                 }
3533                                 tcp_input_data(connp, mp, NULL, ira);
3534                                 return;
3535                         }
3536                         /*
3537                          * This segment contains only the urgent byte.  We
3538                          * have to allocate the T_exdata_ind, if we can.
3539                          */
3540                         if (IPCL_IS_NONSTR(connp)) {
3541                                 int error;
3542 
3543                                 (*sockupcalls->su_recv)
3544                                     (connp->conn_upper_handle, mp, seg_len,
3545                                     MSG_OOB, &error, NULL);
3546                                 /*
3547                                  * We should never be in middle of a
3548                                  * fallback, the squeue guarantees that.
3549                                  */
3550                                 ASSERT(error != EOPNOTSUPP);
3551                                 mp = NULL;
3552                                 goto update_ack;
3553                         } else if (!tcp->tcp_urp_mp) {
3554                                 struct T_exdata_ind *tei;
3555                                 mp1 = allocb(sizeof (struct T_exdata_ind),
3556                                     BPRI_MED);
3557                                 if (!mp1) {
3558                                         /*
3559                                          * Sigh... It'll be back.
3560                                          * Generate any MSG*MARK message now.
3561                                          */
3562                                         freemsg(mp);
3563                                         seg_len = 0;
3564                                         if (flags & TH_SEND_URP_MARK) {
3565 
3566 
3567                                                 ASSERT(tcp->tcp_urp_mark_mp);
3568                                                 tcp->tcp_urp_mark_mp->b_flag &=
3569                                                     ~MSGNOTMARKNEXT;
3570                                                 tcp->tcp_urp_mark_mp->b_flag |=
3571                                                     MSGMARKNEXT;
3572                                         }
3573                                         goto ack_check;
3574                                 }
3575                                 mp1->b_datap->db_type = M_PROTO;
3576                                 tei = (struct T_exdata_ind *)mp1->b_rptr;
3577                                 tei->PRIM_type = T_EXDATA_IND;
3578                                 tei->MORE_flag = 0;
3579                                 mp1->b_wptr = (uchar_t *)&tei[1];
3580                                 tcp->tcp_urp_mp = mp1;
3581 #ifdef DEBUG
3582                                 (void) strlog(TCP_MOD_ID, 0, 1, SL_TRACE,
3583                                     "tcp_rput: allocated exdata_ind %s",
3584                                     tcp_display(tcp, NULL,
3585                                     DISP_PORT_ONLY));
3586 #endif /* DEBUG */
3587                                 /*
3588                                  * There is no need to send a separate MSG*MARK
3589                                  * message since the T_EXDATA_IND will be sent
3590                                  * now.
3591                                  */
3592                                 flags &= ~TH_SEND_URP_MARK;
3593                                 freemsg(tcp->tcp_urp_mark_mp);
3594                                 tcp->tcp_urp_mark_mp = NULL;
3595                         }
3596                         /*
3597                          * Now we are all set.  On the next putnext upstream,
3598                          * tcp_urp_mp will be non-NULL and will get prepended
3599                          * to what has to be this piece containing the urgent
3600                          * byte.  If for any reason we abort this segment below,
3601                          * if it comes back, we will have this ready, or it
3602                          * will get blown off in close.
3603                          */
3604                 } else if (urp == seg_len) {
3605                         /*
3606                          * The urgent byte is the next byte after this sequence
3607                          * number. If this endpoint is non-STREAMS, then there
3608                          * is nothing to do here since the socket has already
3609                          * been notified about the urg pointer by the
3610                          * su_signal_oob call above.
3611                          *
3612                          * In case of STREAMS, some more work might be needed.
3613                          * If there is data it is marked with MSGMARKNEXT and
3614                          * and any tcp_urp_mark_mp is discarded since it is not
3615                          * needed. Otherwise, if the code above just allocated
3616                          * a zero-length tcp_urp_mark_mp message, that message
3617                          * is tagged with MSGMARKNEXT. Sending up these
3618                          * MSGMARKNEXT messages makes SIOCATMARK work correctly
3619                          * even though the T_EXDATA_IND will not be sent up
3620                          * until the urgent byte arrives.
3621                          */
3622                         if (!IPCL_IS_NONSTR(tcp->tcp_connp)) {
3623                                 if (seg_len != 0) {
3624                                         flags |= TH_MARKNEXT_NEEDED;
3625                                         freemsg(tcp->tcp_urp_mark_mp);
3626                                         tcp->tcp_urp_mark_mp = NULL;
3627                                         flags &= ~TH_SEND_URP_MARK;
3628                                 } else if (tcp->tcp_urp_mark_mp != NULL) {
3629                                         flags |= TH_SEND_URP_MARK;
3630                                         tcp->tcp_urp_mark_mp->b_flag &=
3631                                             ~MSGNOTMARKNEXT;
3632                                         tcp->tcp_urp_mark_mp->b_flag |=
3633                                             MSGMARKNEXT;
3634                                 }
3635                         }
3636 #ifdef DEBUG
3637                         (void) strlog(TCP_MOD_ID, 0, 1, SL_TRACE,
3638                             "tcp_rput: AT MARK, len %d, flags 0x%x, %s",
3639                             seg_len, flags,
3640                             tcp_display(tcp, NULL, DISP_PORT_ONLY));
3641 #endif /* DEBUG */
3642                 }
3643 #ifdef DEBUG
3644                 else {
3645                         /* Data left until we hit mark */
3646                         (void) strlog(TCP_MOD_ID, 0, 1, SL_TRACE,
3647                             "tcp_rput: URP %d bytes left, %s",
3648                             urp - seg_len, tcp_display(tcp, NULL,
3649                             DISP_PORT_ONLY));
3650                 }
3651 #endif /* DEBUG */
3652         }
3653 
3654 process_ack:
3655         if (!(flags & TH_ACK)) {
3656                 freemsg(mp);
3657                 goto xmit_check;
3658         }
3659         }
3660         bytes_acked = (int)(seg_ack - tcp->tcp_suna);
3661 
3662         if (bytes_acked > 0)
3663                 tcp->tcp_ip_forward_progress = B_TRUE;
3664         if (tcp->tcp_state == TCPS_SYN_RCVD) {
3665                 /*
3666                  * tcp_sendmsg() checks tcp_state without entering
3667                  * the squeue so tcp_state should be updated before
3668                  * sending up a connection confirmation or a new
3669                  * connection indication.
3670                  */
3671                 tcp->tcp_state = TCPS_ESTABLISHED;
3672 
3673                 /*
3674                  * We are seeing the final ack in the three way
3675                  * hand shake of a active open'ed connection
3676                  * so we must send up a T_CONN_CON
3677                  */
3678                 if (tcp->tcp_active_open) {
3679                         if (!tcp_conn_con(tcp, iphdr, mp, NULL, ira)) {
3680                                 freemsg(mp);
3681                                 tcp->tcp_state = TCPS_SYN_RCVD;
3682                                 return;
3683                         }
3684                         /*
3685                          * Don't fuse the loopback endpoints for
3686                          * simultaneous active opens.
3687                          */
3688                         if (tcp->tcp_loopback) {
3689                                 TCP_STAT(tcps, tcp_fusion_unfusable);
3690                                 tcp->tcp_unfusable = B_TRUE;
3691                         }
3692                         /*
3693                          * For simultaneous active open, trace receipt of final
3694                          * ACK as tcp:::connect-established.
3695                          */
3696                         DTRACE_TCP5(connect__established, mblk_t *, NULL,
3697                             ip_xmit_attr_t *, connp->conn_ixa, void_ip_t *,
3698                             iphdr, tcp_t *, tcp, tcph_t *, tcpha);
3699                 } else if (IPCL_IS_NONSTR(connp)) {
3700                         /*
3701                          * 3-way handshake has completed, so notify socket
3702                          * of the new connection.
3703                          *
3704                          * We are here means eager is fine but it can
3705                          * get a TH_RST at any point between now and till
3706                          * accept completes and disappear. We need to
3707                          * ensure that reference to eager is valid after
3708                          * we get out of eager's perimeter. So we do
3709                          * an extra refhold.
3710                          */
3711                         CONN_INC_REF(connp);
3712 
3713                         if (!tcp_newconn_notify(tcp, ira)) {
3714                                 /*
3715                                  * The state-change probe for SYN_RCVD ->
3716                                  * ESTABLISHED has not fired yet. We reset
3717                                  * the state to SYN_RCVD so that future
3718                                  * state-change probes report correct state
3719                                  * transistions.
3720                                  */
3721                                 tcp->tcp_state = TCPS_SYN_RCVD;
3722                                 freemsg(mp);
3723                                 /* notification did not go up, so drop ref */
3724                                 CONN_DEC_REF(connp);
3725                                 /* ... and close the eager */
3726                                 ASSERT(TCP_IS_DETACHED(tcp));
3727                                 (void) tcp_close_detached(tcp);
3728                                 return;
3729                         }
3730                         /*
3731                          * tcp_newconn_notify() changes conn_upcalls and
3732                          * connp->conn_upper_handle.  Fix things now, in case
3733                          * there's data attached to this ack.
3734                          */
3735                         if (connp->conn_upcalls != NULL)
3736                                 sockupcalls = connp->conn_upcalls;
3737                         /*
3738                          * For passive open, trace receipt of final ACK as
3739                          * tcp:::accept-established.
3740                          */
3741                         DTRACE_TCP5(accept__established, mlbk_t *, NULL,
3742                             ip_xmit_attr_t *, connp->conn_ixa, void_ip_t *,
3743                             iphdr, tcp_t *, tcp, tcph_t *, tcpha);
3744                 } else {
3745                         /*
3746                          * 3-way handshake complete - this is a STREAMS based
3747                          * socket, so pass up the T_CONN_IND.
3748                          */
3749                         tcp_t   *listener = tcp->tcp_listener;
3750                         mblk_t  *mp = tcp->tcp_conn.tcp_eager_conn_ind;
3751 
3752                         tcp->tcp_tconnind_started = B_TRUE;
3753                         tcp->tcp_conn.tcp_eager_conn_ind = NULL;
3754                         ASSERT(mp != NULL);
3755                         /*
3756                          * We are here means eager is fine but it can
3757                          * get a TH_RST at any point between now and till
3758                          * accept completes and disappear. We need to
3759                          * ensure that reference to eager is valid after
3760                          * we get out of eager's perimeter. So we do
3761                          * an extra refhold.
3762                          */
3763                         CONN_INC_REF(connp);
3764 
3765                         /*
3766                          * The listener also exists because of the refhold
3767                          * done in tcp_input_listener. Its possible that it
3768                          * might have closed. We will check that once we
3769                          * get inside listeners context.
3770                          */
3771                         CONN_INC_REF(listener->tcp_connp);
3772                         if (listener->tcp_connp->conn_sqp ==
3773                             connp->conn_sqp) {
3774                                 /*
3775                                  * We optimize by not calling an SQUEUE_ENTER
3776                                  * on the listener since we know that the
3777                                  * listener and eager squeues are the same.
3778                                  * We are able to make this check safely only
3779                                  * because neither the eager nor the listener
3780                                  * can change its squeue. Only an active connect
3781                                  * can change its squeue
3782                                  */
3783                                 tcp_send_conn_ind(listener->tcp_connp, mp,
3784                                     listener->tcp_connp->conn_sqp);
3785                                 CONN_DEC_REF(listener->tcp_connp);
3786                         } else if (!tcp->tcp_loopback) {
3787                                 SQUEUE_ENTER_ONE(listener->tcp_connp->conn_sqp,
3788                                     mp, tcp_send_conn_ind,
3789                                     listener->tcp_connp, NULL, SQ_FILL,
3790                                     SQTAG_TCP_CONN_IND);
3791                         } else {
3792                                 SQUEUE_ENTER_ONE(listener->tcp_connp->conn_sqp,
3793                                     mp, tcp_send_conn_ind,
3794                                     listener->tcp_connp, NULL, SQ_NODRAIN,
3795                                     SQTAG_TCP_CONN_IND);
3796                         }
3797                         /*
3798                          * For passive open, trace receipt of final ACK as
3799                          * tcp:::accept-established.
3800                          */
3801                         DTRACE_TCP5(accept__established, mlbk_t *, NULL,
3802                             ip_xmit_attr_t *, connp->conn_ixa, void_ip_t *,
3803                             iphdr, tcp_t *, tcp, tcph_t *, tcpha);
3804                 }
3805                 TCPS_CONN_INC(tcps);
3806 
3807                 tcp->tcp_suna = tcp->tcp_iss + 1; /* One for the SYN */
3808                 bytes_acked--;
3809                 /* SYN was acked - making progress */
3810                 tcp->tcp_ip_forward_progress = B_TRUE;
3811 
3812                 /*
3813                  * If SYN was retransmitted, need to reset all
3814                  * retransmission info as this segment will be
3815                  * treated as a dup ACK.
3816                  */
3817                 if (tcp->tcp_rexmit) {
3818                         tcp->tcp_rexmit = B_FALSE;
3819                         tcp->tcp_rexmit_nxt = tcp->tcp_snxt;
3820                         tcp->tcp_rexmit_max = tcp->tcp_snxt;
3821                         tcp->tcp_ms_we_have_waited = 0;
3822                         tcp->tcp_cwnd = mss;
3823                 }
3824 
3825                 /*
3826                  * We set the send window to zero here.
3827                  * This is needed if there is data to be
3828                  * processed already on the queue.
3829                  * Later (at swnd_update label), the
3830                  * "new_swnd > tcp_swnd" condition is satisfied
3831                  * the XMIT_NEEDED flag is set in the current
3832                  * (SYN_RCVD) state. This ensures tcp_wput_data() is
3833                  * called if there is already data on queue in
3834                  * this state.
3835                  */
3836                 tcp->tcp_swnd = 0;
3837 
3838                 if (new_swnd > tcp->tcp_max_swnd)
3839                         tcp->tcp_max_swnd = new_swnd;
3840                 tcp->tcp_swl1 = seg_seq;
3841                 tcp->tcp_swl2 = seg_ack;
3842                 tcp->tcp_valid_bits &= ~TCP_ISS_VALID;
3843 
3844                 /* Trace change from SYN_RCVD -> ESTABLISHED here */
3845                 DTRACE_TCP6(state__change, void, NULL, ip_xmit_attr_t *,
3846                     connp->conn_ixa, void, NULL, tcp_t *, tcp, void, NULL,
3847                     int32_t, TCPS_SYN_RCVD);
3848 
3849                 /* Fuse when both sides are in ESTABLISHED state */
3850                 if (tcp->tcp_loopback && do_tcp_fusion)
3851                         tcp_fuse(tcp, iphdr, tcpha);
3852 
3853         }
3854         /* This code follows 4.4BSD-Lite2 mostly. */
3855         if (bytes_acked < 0)
3856                 goto est;
3857 
3858         /*
3859          * If TCP is ECN capable and the congestion experience bit is
3860          * set, reduce tcp_cwnd and tcp_ssthresh.  But this should only be
3861          * done once per window (or more loosely, per RTT).
3862          */
3863         if (tcp->tcp_cwr && SEQ_GT(seg_ack, tcp->tcp_cwr_snd_max))
3864                 tcp->tcp_cwr = B_FALSE;
3865         if (tcp->tcp_ecn_ok && (flags & TH_ECE)) {
3866                 if (!tcp->tcp_cwr) {
3867                         npkt = ((tcp->tcp_snxt - tcp->tcp_suna) >> 1) / mss;
3868                         tcp->tcp_cwnd_ssthresh = MAX(npkt, 2) * mss;
3869                         tcp->tcp_cwnd = npkt * mss;
3870                         /*
3871                          * If the cwnd is 0, use the timer to clock out
3872                          * new segments.  This is required by the ECN spec.
3873                          */
3874                         if (npkt == 0) {
3875                                 TCP_TIMER_RESTART(tcp, tcp->tcp_rto);
3876                                 /*
3877                                  * This makes sure that when the ACK comes
3878                                  * back, we will increase tcp_cwnd by 1 MSS.
3879                                  */
3880                                 tcp->tcp_cwnd_cnt = 0;
3881                         }
3882                         tcp->tcp_cwr = B_TRUE;
3883                         /*
3884                          * This marks the end of the current window of in
3885                          * flight data.  That is why we don't use
3886                          * tcp_suna + tcp_swnd.  Only data in flight can
3887                          * provide ECN info.
3888                          */
3889                         tcp->tcp_cwr_snd_max = tcp->tcp_snxt;
3890                         tcp->tcp_ecn_cwr_sent = B_FALSE;
3891                 }
3892         }
3893 
3894         mp1 = tcp->tcp_xmit_head;
3895         if (bytes_acked == 0) {
3896                 if (!ofo_seg && seg_len == 0 && new_swnd == tcp->tcp_swnd) {
3897                         int dupack_cnt;
3898 
3899                         TCPS_BUMP_MIB(tcps, tcpInDupAck);
3900                         /*
3901                          * Fast retransmit.  When we have seen exactly three
3902                          * identical ACKs while we have unacked data
3903                          * outstanding we take it as a hint that our peer
3904                          * dropped something.
3905                          *
3906                          * If TCP is retransmitting, don't do fast retransmit.
3907                          */
3908                         if (mp1 && tcp->tcp_suna != tcp->tcp_snxt &&
3909                             ! tcp->tcp_rexmit) {
3910                                 /* Do Limited Transmit */
3911                                 if ((dupack_cnt = ++tcp->tcp_dupack_cnt) <
3912                                     tcps->tcps_dupack_fast_retransmit) {
3913                                         /*
3914                                          * RFC 3042
3915                                          *
3916                                          * What we need to do is temporarily
3917                                          * increase tcp_cwnd so that new
3918                                          * data can be sent if it is allowed
3919                                          * by the receive window (tcp_rwnd).
3920                                          * tcp_wput_data() will take care of
3921                                          * the rest.
3922                                          *
3923                                          * If the connection is SACK capable,
3924                                          * only do limited xmit when there
3925                                          * is SACK info.
3926                                          *
3927                                          * Note how tcp_cwnd is incremented.
3928                                          * The first dup ACK will increase
3929                                          * it by 1 MSS.  The second dup ACK
3930                                          * will increase it by 2 MSS.  This
3931                                          * means that only 1 new segment will
3932                                          * be sent for each dup ACK.
3933                                          */
3934                                         if (tcp->tcp_unsent > 0 &&
3935                                             (!tcp->tcp_snd_sack_ok ||
3936                                             (tcp->tcp_snd_sack_ok &&
3937                                             tcp->tcp_notsack_list != NULL))) {
3938                                                 tcp->tcp_cwnd += mss <<
3939                                                     (tcp->tcp_dupack_cnt - 1);
3940                                                 flags |= TH_LIMIT_XMIT;
3941                                         }
3942                                 } else if (dupack_cnt ==
3943                                     tcps->tcps_dupack_fast_retransmit) {
3944 
3945                                 /*
3946                                  * If we have reduced tcp_ssthresh
3947                                  * because of ECN, do not reduce it again
3948                                  * unless it is already one window of data
3949                                  * away.  After one window of data, tcp_cwr
3950                                  * should then be cleared.  Note that
3951                                  * for non ECN capable connection, tcp_cwr
3952                                  * should always be false.
3953                                  *
3954                                  * Adjust cwnd since the duplicate
3955                                  * ack indicates that a packet was
3956                                  * dropped (due to congestion.)
3957                                  */
3958                                 if (!tcp->tcp_cwr) {
3959                                         npkt = ((tcp->tcp_snxt -
3960                                             tcp->tcp_suna) >> 1) / mss;
3961                                         tcp->tcp_cwnd_ssthresh = MAX(npkt, 2) *
3962                                             mss;
3963                                         tcp->tcp_cwnd = (npkt +
3964                                             tcp->tcp_dupack_cnt) * mss;
3965                                 }
3966                                 if (tcp->tcp_ecn_ok) {
3967                                         tcp->tcp_cwr = B_TRUE;
3968                                         tcp->tcp_cwr_snd_max = tcp->tcp_snxt;
3969                                         tcp->tcp_ecn_cwr_sent = B_FALSE;
3970                                 }
3971 
3972                                 /*
3973                                  * We do Hoe's algorithm.  Refer to her
3974                                  * paper "Improving the Start-up Behavior
3975                                  * of a Congestion Control Scheme for TCP,"
3976                                  * appeared in SIGCOMM'96.
3977                                  *
3978                                  * Save highest seq no we have sent so far.
3979                                  * Be careful about the invisible FIN byte.
3980                                  */
3981                                 if ((tcp->tcp_valid_bits & TCP_FSS_VALID) &&
3982                                     (tcp->tcp_unsent == 0)) {
3983                                         tcp->tcp_rexmit_max = tcp->tcp_fss;
3984                                 } else {
3985                                         tcp->tcp_rexmit_max = tcp->tcp_snxt;
3986                                 }
3987 
3988                                 /*
3989                                  * For SACK:
3990                                  * Calculate tcp_pipe, which is the
3991                                  * estimated number of bytes in
3992                                  * network.
3993                                  *
3994                                  * tcp_fack is the highest sack'ed seq num
3995                                  * TCP has received.
3996                                  *
3997                                  * tcp_pipe is explained in the above quoted
3998                                  * Fall and Floyd's paper.  tcp_fack is
3999                                  * explained in Mathis and Mahdavi's
4000                                  * "Forward Acknowledgment: Refining TCP
4001                                  * Congestion Control" in SIGCOMM '96.
4002                                  */
4003                                 if (tcp->tcp_snd_sack_ok) {
4004                                         if (tcp->tcp_notsack_list != NULL) {
4005                                                 tcp->tcp_pipe = tcp->tcp_snxt -
4006                                                     tcp->tcp_fack;
4007                                                 tcp->tcp_sack_snxt = seg_ack;
4008                                                 flags |= TH_NEED_SACK_REXMIT;
4009                                         } else {
4010                                                 /*
4011                                                  * Always initialize tcp_pipe
4012                                                  * even though we don't have
4013                                                  * any SACK info.  If later
4014                                                  * we get SACK info and
4015                                                  * tcp_pipe is not initialized,
4016                                                  * funny things will happen.
4017                                                  */
4018                                                 tcp->tcp_pipe =
4019                                                     tcp->tcp_cwnd_ssthresh;
4020                                         }
4021                                 } else {
4022                                         flags |= TH_REXMIT_NEEDED;
4023                                 } /* tcp_snd_sack_ok */
4024 
4025                                 } else {
4026                                         /*
4027                                          * Here we perform congestion
4028                                          * avoidance, but NOT slow start.
4029                                          * This is known as the Fast
4030                                          * Recovery Algorithm.
4031                                          */
4032                                         if (tcp->tcp_snd_sack_ok &&
4033                                             tcp->tcp_notsack_list != NULL) {
4034                                                 flags |= TH_NEED_SACK_REXMIT;
4035                                                 tcp->tcp_pipe -= mss;
4036                                                 if (tcp->tcp_pipe < 0)
4037                                                         tcp->tcp_pipe = 0;
4038                                         } else {
4039                                         /*
4040                                          * We know that one more packet has
4041                                          * left the pipe thus we can update
4042                                          * cwnd.
4043                                          */
4044                                         cwnd = tcp->tcp_cwnd + mss;
4045                                         if (cwnd > tcp->tcp_cwnd_max)
4046                                                 cwnd = tcp->tcp_cwnd_max;
4047                                         tcp->tcp_cwnd = cwnd;
4048                                         if (tcp->tcp_unsent > 0)
4049                                                 flags |= TH_XMIT_NEEDED;
4050                                         }
4051                                 }
4052                         }
4053                 } else if (tcp->tcp_zero_win_probe) {
4054                         /*
4055                          * If the window has opened, need to arrange
4056                          * to send additional data.
4057                          */
4058                         if (new_swnd != 0) {
4059                                 /* tcp_suna != tcp_snxt */
4060                                 /* Packet contains a window update */
4061                                 TCPS_BUMP_MIB(tcps, tcpInWinUpdate);
4062                                 tcp->tcp_zero_win_probe = 0;
4063                                 tcp->tcp_timer_backoff = 0;
4064                                 tcp->tcp_ms_we_have_waited = 0;
4065 
4066                                 /*
4067                                  * Transmit starting with tcp_suna since
4068                                  * the one byte probe is not ack'ed.
4069                                  * If TCP has sent more than one identical
4070                                  * probe, tcp_rexmit will be set.  That means
4071                                  * tcp_ss_rexmit() will send out the one
4072                                  * byte along with new data.  Otherwise,
4073                                  * fake the retransmission.
4074                                  */
4075                                 flags |= TH_XMIT_NEEDED;
4076                                 if (!tcp->tcp_rexmit) {
4077                                         tcp->tcp_rexmit = B_TRUE;
4078                                         tcp->tcp_dupack_cnt = 0;
4079                                         tcp->tcp_rexmit_nxt = tcp->tcp_suna;
4080                                         tcp->tcp_rexmit_max = tcp->tcp_suna + 1;
4081                                 }
4082                         }
4083                 }
4084                 goto swnd_update;
4085         }
4086 
4087         /*
4088          * Check for "acceptability" of ACK value per RFC 793, pages 72 - 73.
4089          * If the ACK value acks something that we have not yet sent, it might
4090          * be an old duplicate segment.  Send an ACK to re-synchronize the
4091          * other side.
4092          * Note: reset in response to unacceptable ACK in SYN_RECEIVE
4093          * state is handled above, so we can always just drop the segment and
4094          * send an ACK here.
4095          *
4096          * In the case where the peer shrinks the window, we see the new window
4097          * update, but all the data sent previously is queued up by the peer.
4098          * To account for this, in tcp_process_shrunk_swnd(), the sequence
4099          * number, which was already sent, and within window, is recorded.
4100          * tcp_snxt is then updated.
4101          *
4102          * If the window has previously shrunk, and an ACK for data not yet
4103          * sent, according to tcp_snxt is recieved, it may still be valid. If
4104          * the ACK is for data within the window at the time the window was
4105          * shrunk, then the ACK is acceptable. In this case tcp_snxt is set to
4106          * the sequence number ACK'ed.
4107          *
4108          * If the ACK covers all the data sent at the time the window was
4109          * shrunk, we can now set tcp_is_wnd_shrnk to B_FALSE.
4110          *
4111          * Should we send ACKs in response to ACK only segments?
4112          */
4113 
4114         if (SEQ_GT(seg_ack, tcp->tcp_snxt)) {
4115                 if ((tcp->tcp_is_wnd_shrnk) &&
4116                     (SEQ_LEQ(seg_ack, tcp->tcp_snxt_shrunk))) {
4117                         uint32_t data_acked_ahead_snxt;
4118 
4119                         data_acked_ahead_snxt = seg_ack - tcp->tcp_snxt;
4120                         tcp_update_xmit_tail(tcp, seg_ack);
4121                         tcp->tcp_unsent -= data_acked_ahead_snxt;
4122                 } else {
4123                         TCPS_BUMP_MIB(tcps, tcpInAckUnsent);
4124                         /* drop the received segment */
4125                         freemsg(mp);
4126 
4127                         /*
4128                          * Send back an ACK.  If tcp_drop_ack_unsent_cnt is
4129                          * greater than 0, check if the number of such
4130                          * bogus ACks is greater than that count.  If yes,
4131                          * don't send back any ACK.  This prevents TCP from
4132                          * getting into an ACK storm if somehow an attacker
4133                          * successfully spoofs an acceptable segment to our
4134                          * peer.  If this continues (count > 2 X threshold),
4135                          * we should abort this connection.
4136                          */
4137                         if (tcp_drop_ack_unsent_cnt > 0 &&
4138                             ++tcp->tcp_in_ack_unsent >
4139                             tcp_drop_ack_unsent_cnt) {
4140                                 TCP_STAT(tcps, tcp_in_ack_unsent_drop);
4141                                 if (tcp->tcp_in_ack_unsent > 2 *
4142                                     tcp_drop_ack_unsent_cnt) {
4143                                         (void) tcp_clean_death(tcp, EPROTO);
4144                                 }
4145                                 return;
4146                         }
4147                         mp = tcp_ack_mp(tcp);
4148                         if (mp != NULL) {
4149                                 BUMP_LOCAL(tcp->tcp_obsegs);
4150                                 TCPS_BUMP_MIB(tcps, tcpOutAck);
4151                                 tcp_send_data(tcp, mp);
4152                         }
4153                         return;
4154                 }
4155         } else if (tcp->tcp_is_wnd_shrnk && SEQ_GEQ(seg_ack,
4156             tcp->tcp_snxt_shrunk)) {
4157                         tcp->tcp_is_wnd_shrnk = B_FALSE;
4158         }
4159 
4160         /*
4161          * TCP gets a new ACK, update the notsack'ed list to delete those
4162          * blocks that are covered by this ACK.
4163          */
4164         if (tcp->tcp_snd_sack_ok && tcp->tcp_notsack_list != NULL) {
4165                 tcp_notsack_remove(&(tcp->tcp_notsack_list), seg_ack,
4166                     &(tcp->tcp_num_notsack_blk), &(tcp->tcp_cnt_notsack_list));
4167         }
4168 
4169         /*
4170          * If we got an ACK after fast retransmit, check to see
4171          * if it is a partial ACK.  If it is not and the congestion
4172          * window was inflated to account for the other side's
4173          * cached packets, retract it.  If it is, do Hoe's algorithm.
4174          */
4175         if (tcp->tcp_dupack_cnt >= tcps->tcps_dupack_fast_retransmit) {
4176                 ASSERT(tcp->tcp_rexmit == B_FALSE);
4177                 if (SEQ_GEQ(seg_ack, tcp->tcp_rexmit_max)) {
4178                         tcp->tcp_dupack_cnt = 0;
4179                         /*
4180                          * Restore the orig tcp_cwnd_ssthresh after
4181                          * fast retransmit phase.
4182                          */
4183                         if (tcp->tcp_cwnd > tcp->tcp_cwnd_ssthresh) {
4184                                 tcp->tcp_cwnd = tcp->tcp_cwnd_ssthresh;
4185                         }
4186                         tcp->tcp_rexmit_max = seg_ack;
4187                         tcp->tcp_cwnd_cnt = 0;
4188 
4189                         /*
4190                          * Remove all notsack info to avoid confusion with
4191                          * the next fast retrasnmit/recovery phase.
4192                          */
4193                         if (tcp->tcp_snd_sack_ok) {
4194                                 TCP_NOTSACK_REMOVE_ALL(tcp->tcp_notsack_list,
4195                                     tcp);
4196                         }
4197                 } else {
4198                         if (tcp->tcp_snd_sack_ok &&
4199                             tcp->tcp_notsack_list != NULL) {
4200                                 flags |= TH_NEED_SACK_REXMIT;
4201                                 tcp->tcp_pipe -= mss;
4202                                 if (tcp->tcp_pipe < 0)
4203                                         tcp->tcp_pipe = 0;
4204                         } else {
4205                                 /*
4206                                  * Hoe's algorithm:
4207                                  *
4208                                  * Retransmit the unack'ed segment and
4209                                  * restart fast recovery.  Note that we
4210                                  * need to scale back tcp_cwnd to the
4211                                  * original value when we started fast
4212                                  * recovery.  This is to prevent overly
4213                                  * aggressive behaviour in sending new
4214                                  * segments.
4215                                  */
4216                                 tcp->tcp_cwnd = tcp->tcp_cwnd_ssthresh +
4217                                     tcps->tcps_dupack_fast_retransmit * mss;
4218                                 tcp->tcp_cwnd_cnt = tcp->tcp_cwnd;
4219                                 flags |= TH_REXMIT_NEEDED;
4220                         }
4221                 }
4222         } else {
4223                 tcp->tcp_dupack_cnt = 0;
4224                 if (tcp->tcp_rexmit) {
4225                         /*
4226                          * TCP is retranmitting.  If the ACK ack's all
4227                          * outstanding data, update tcp_rexmit_max and
4228                          * tcp_rexmit_nxt.  Otherwise, update tcp_rexmit_nxt
4229                          * to the correct value.
4230                          *
4231                          * Note that SEQ_LEQ() is used.  This is to avoid
4232                          * unnecessary fast retransmit caused by dup ACKs
4233                          * received when TCP does slow start retransmission
4234                          * after a time out.  During this phase, TCP may
4235                          * send out segments which are already received.
4236                          * This causes dup ACKs to be sent back.
4237                          */
4238                         if (SEQ_LEQ(seg_ack, tcp->tcp_rexmit_max)) {
4239                                 if (SEQ_GT(seg_ack, tcp->tcp_rexmit_nxt)) {
4240                                         tcp->tcp_rexmit_nxt = seg_ack;
4241                                 }
4242                                 if (seg_ack != tcp->tcp_rexmit_max) {
4243                                         flags |= TH_XMIT_NEEDED;
4244                                 }
4245                         } else {
4246                                 tcp->tcp_rexmit = B_FALSE;
4247                                 tcp->tcp_rexmit_nxt = tcp->tcp_snxt;
4248                         }
4249                         tcp->tcp_ms_we_have_waited = 0;
4250                 }
4251         }
4252 
4253         TCPS_BUMP_MIB(tcps, tcpInAckSegs);
4254         TCPS_UPDATE_MIB(tcps, tcpInAckBytes, bytes_acked);
4255         tcp->tcp_suna = seg_ack;
4256         if (tcp->tcp_zero_win_probe != 0) {
4257                 tcp->tcp_zero_win_probe = 0;
4258                 tcp->tcp_timer_backoff = 0;
4259         }
4260 
4261         /*
4262          * If tcp_xmit_head is NULL, then it must be the FIN being ack'ed.
4263          * Note that it cannot be the SYN being ack'ed.  The code flow
4264          * will not reach here.
4265          */
4266         if (mp1 == NULL) {
4267                 goto fin_acked;
4268         }
4269 
4270         /*
4271          * Update the congestion window.
4272          *
4273          * If TCP is not ECN capable or TCP is ECN capable but the
4274          * congestion experience bit is not set, increase the tcp_cwnd as
4275          * usual.
4276          */
4277         if (!tcp->tcp_ecn_ok || !(flags & TH_ECE)) {
4278                 cwnd = tcp->tcp_cwnd;
4279                 add = mss;
4280 
4281                 if (cwnd >= tcp->tcp_cwnd_ssthresh) {
4282                         /*
4283                          * This is to prevent an increase of less than 1 MSS of
4284                          * tcp_cwnd.  With partial increase, tcp_wput_data()
4285                          * may send out tinygrams in order to preserve mblk
4286                          * boundaries.
4287                          *
4288                          * By initializing tcp_cwnd_cnt to new tcp_cwnd and
4289                          * decrementing it by 1 MSS for every ACKs, tcp_cwnd is
4290                          * increased by 1 MSS for every RTTs.
4291                          */
4292                         if (tcp->tcp_cwnd_cnt <= 0) {
4293                                 tcp->tcp_cwnd_cnt = cwnd + add;
4294                         } else {
4295                                 tcp->tcp_cwnd_cnt -= add;
4296                                 add = 0;
4297                         }
4298                 }
4299                 tcp->tcp_cwnd = MIN(cwnd + add, tcp->tcp_cwnd_max);
4300         }
4301 
4302         /* See if the latest urgent data has been acknowledged */
4303         if ((tcp->tcp_valid_bits & TCP_URG_VALID) &&
4304             SEQ_GT(seg_ack, tcp->tcp_urg))
4305                 tcp->tcp_valid_bits &= ~TCP_URG_VALID;
4306 
4307         /* Can we update the RTT estimates? */
4308         if (tcp->tcp_snd_ts_ok) {
4309                 /* Ignore zero timestamp echo-reply. */
4310                 if (tcpopt.tcp_opt_ts_ecr != 0) {
4311                         tcp_set_rto(tcp, (int32_t)LBOLT_FASTPATH -
4312                             (int32_t)tcpopt.tcp_opt_ts_ecr);
4313                 }
4314 
4315                 /* If needed, restart the timer. */
4316                 if (tcp->tcp_set_timer == 1) {
4317                         TCP_TIMER_RESTART(tcp, tcp->tcp_rto);
4318                         tcp->tcp_set_timer = 0;
4319                 }
4320                 /*
4321                  * Update tcp_csuna in case the other side stops sending
4322                  * us timestamps.
4323                  */
4324                 tcp->tcp_csuna = tcp->tcp_snxt;
4325         } else if (SEQ_GT(seg_ack, tcp->tcp_csuna)) {
4326                 /*
4327                  * An ACK sequence we haven't seen before, so get the RTT
4328                  * and update the RTO. But first check if the timestamp is
4329                  * valid to use.
4330                  */
4331                 if ((mp1->b_next != NULL) &&
4332                     SEQ_GT(seg_ack, (uint32_t)(uintptr_t)(mp1->b_next)))
4333                         tcp_set_rto(tcp, (int32_t)LBOLT_FASTPATH -
4334                             (int32_t)(intptr_t)mp1->b_prev);
4335                 else
4336                         TCPS_BUMP_MIB(tcps, tcpRttNoUpdate);
4337 
4338                 /* Remeber the last sequence to be ACKed */
4339                 tcp->tcp_csuna = seg_ack;
4340                 if (tcp->tcp_set_timer == 1) {
4341                         TCP_TIMER_RESTART(tcp, tcp->tcp_rto);
4342                         tcp->tcp_set_timer = 0;
4343                 }
4344         } else {
4345                 TCPS_BUMP_MIB(tcps, tcpRttNoUpdate);
4346         }
4347 
4348         /* Eat acknowledged bytes off the xmit queue. */
4349         for (;;) {
4350                 mblk_t  *mp2;
4351                 uchar_t *wptr;
4352 
4353                 wptr = mp1->b_wptr;
4354                 ASSERT((uintptr_t)(wptr - mp1->b_rptr) <= (uintptr_t)INT_MAX);
4355                 bytes_acked -= (int)(wptr - mp1->b_rptr);
4356                 if (bytes_acked < 0) {
4357                         mp1->b_rptr = wptr + bytes_acked;
4358                         /*
4359                          * Set a new timestamp if all the bytes timed by the
4360                          * old timestamp have been ack'ed.
4361                          */
4362                         if (SEQ_GT(seg_ack,
4363                             (uint32_t)(uintptr_t)(mp1->b_next))) {
4364                                 mp1->b_prev =
4365                                     (mblk_t *)(uintptr_t)LBOLT_FASTPATH;
4366                                 mp1->b_next = NULL;
4367                         }
4368                         break;
4369                 }
4370                 mp1->b_next = NULL;
4371                 mp1->b_prev = NULL;
4372                 mp2 = mp1;
4373                 mp1 = mp1->b_cont;
4374 
4375                 /*
4376                  * This notification is required for some zero-copy
4377                  * clients to maintain a copy semantic. After the data
4378                  * is ack'ed, client is safe to modify or reuse the buffer.
4379                  */
4380                 if (tcp->tcp_snd_zcopy_aware &&
4381                     (mp2->b_datap->db_struioflag & STRUIO_ZCNOTIFY))
4382                         tcp_zcopy_notify(tcp);
4383                 freeb(mp2);
4384                 if (bytes_acked == 0) {
4385                         if (mp1 == NULL) {
4386                                 /* Everything is ack'ed, clear the tail. */
4387                                 tcp->tcp_xmit_tail = NULL;
4388                                 /*
4389                                  * Cancel the timer unless we are still
4390                                  * waiting for an ACK for the FIN packet.
4391                                  */
4392                                 if (tcp->tcp_timer_tid != 0 &&
4393                                     tcp->tcp_snxt == tcp->tcp_suna) {
4394                                         (void) TCP_TIMER_CANCEL(tcp,
4395                                             tcp->tcp_timer_tid);
4396                                         tcp->tcp_timer_tid = 0;
4397                                 }
4398                                 goto pre_swnd_update;
4399                         }
4400                         if (mp2 != tcp->tcp_xmit_tail)
4401                                 break;
4402                         tcp->tcp_xmit_tail = mp1;
4403                         ASSERT((uintptr_t)(mp1->b_wptr - mp1->b_rptr) <=
4404                             (uintptr_t)INT_MAX);
4405                         tcp->tcp_xmit_tail_unsent = (int)(mp1->b_wptr -
4406                             mp1->b_rptr);
4407                         break;
4408                 }
4409                 if (mp1 == NULL) {
4410                         /*
4411                          * More was acked but there is nothing more
4412                          * outstanding.  This means that the FIN was
4413                          * just acked or that we're talking to a clown.
4414                          */
4415 fin_acked:
4416                         ASSERT(tcp->tcp_fin_sent);
4417                         tcp->tcp_xmit_tail = NULL;
4418                         if (tcp->tcp_fin_sent) {
4419                                 /* FIN was acked - making progress */
4420                                 if (!tcp->tcp_fin_acked)
4421                                         tcp->tcp_ip_forward_progress = B_TRUE;
4422                                 tcp->tcp_fin_acked = B_TRUE;
4423                                 if (tcp->tcp_linger_tid != 0 &&
4424                                     TCP_TIMER_CANCEL(tcp,
4425                                     tcp->tcp_linger_tid) >= 0) {
4426                                         tcp_stop_lingering(tcp);
4427                                         freemsg(mp);
4428                                         mp = NULL;
4429                                 }
4430                         } else {
4431                                 /*
4432                                  * We should never get here because
4433                                  * we have already checked that the
4434                                  * number of bytes ack'ed should be
4435                                  * smaller than or equal to what we
4436                                  * have sent so far (it is the
4437                                  * acceptability check of the ACK).
4438                                  * We can only get here if the send
4439                                  * queue is corrupted.
4440                                  *
4441                                  * Terminate the connection and
4442                                  * panic the system.  It is better
4443                                  * for us to panic instead of
4444                                  * continuing to avoid other disaster.
4445                                  */
4446                                 tcp_xmit_ctl(NULL, tcp, tcp->tcp_snxt,
4447                                     tcp->tcp_rnxt, TH_RST|TH_ACK);
4448                                 panic("Memory corruption "
4449                                     "detected for connection %s.",
4450                                     tcp_display(tcp, NULL,
4451                                     DISP_ADDR_AND_PORT));
4452                                 /*NOTREACHED*/
4453                         }
4454                         goto pre_swnd_update;
4455                 }
4456                 ASSERT(mp2 != tcp->tcp_xmit_tail);
4457         }
4458         if (tcp->tcp_unsent) {
4459                 flags |= TH_XMIT_NEEDED;
4460         }
4461 pre_swnd_update:
4462         tcp->tcp_xmit_head = mp1;
4463 swnd_update:
4464         /*
4465          * The following check is different from most other implementations.
4466          * For bi-directional transfer, when segments are dropped, the
4467          * "normal" check will not accept a window update in those
4468          * retransmitted segemnts.  Failing to do that, TCP may send out
4469          * segments which are outside receiver's window.  As TCP accepts
4470          * the ack in those retransmitted segments, if the window update in
4471          * the same segment is not accepted, TCP will incorrectly calculates
4472          * that it can send more segments.  This can create a deadlock
4473          * with the receiver if its window becomes zero.
4474          */
4475         if (SEQ_LT(tcp->tcp_swl2, seg_ack) ||
4476             SEQ_LT(tcp->tcp_swl1, seg_seq) ||
4477             (tcp->tcp_swl1 == seg_seq && new_swnd > tcp->tcp_swnd)) {
4478                 /*
4479                  * The criteria for update is:
4480                  *
4481                  * 1. the segment acknowledges some data.  Or
4482                  * 2. the segment is new, i.e. it has a higher seq num. Or
4483                  * 3. the segment is not old and the advertised window is
4484                  * larger than the previous advertised window.
4485                  */
4486                 if (tcp->tcp_unsent && new_swnd > tcp->tcp_swnd)
4487                         flags |= TH_XMIT_NEEDED;
4488                 tcp->tcp_swnd = new_swnd;
4489                 if (new_swnd > tcp->tcp_max_swnd)
4490                         tcp->tcp_max_swnd = new_swnd;
4491                 tcp->tcp_swl1 = seg_seq;
4492                 tcp->tcp_swl2 = seg_ack;
4493         }
4494 est:
4495         if (tcp->tcp_state > TCPS_ESTABLISHED) {
4496 
4497                 switch (tcp->tcp_state) {
4498                 case TCPS_FIN_WAIT_1:
4499                         if (tcp->tcp_fin_acked) {
4500                                 tcp->tcp_state = TCPS_FIN_WAIT_2;
4501                                 DTRACE_TCP6(state__change, void, NULL,
4502                                     ip_xmit_attr_t *, connp->conn_ixa,
4503                                     void, NULL, tcp_t *, tcp, void, NULL,
4504                                     int32_t, TCPS_FIN_WAIT_1);
4505                                 /*
4506                                  * We implement the non-standard BSD/SunOS
4507                                  * FIN_WAIT_2 flushing algorithm.
4508                                  * If there is no user attached to this
4509                                  * TCP endpoint, then this TCP struct
4510                                  * could hang around forever in FIN_WAIT_2
4511                                  * state if the peer forgets to send us
4512                                  * a FIN.  To prevent this, we wait only
4513                                  * 2*MSL (a convenient time value) for
4514                                  * the FIN to arrive.  If it doesn't show up,
4515                                  * we flush the TCP endpoint.  This algorithm,
4516                                  * though a violation of RFC-793, has worked
4517                                  * for over 10 years in BSD systems.
4518                                  * Note: SunOS 4.x waits 675 seconds before
4519                                  * flushing the FIN_WAIT_2 connection.
4520                                  */
4521                                 TCP_TIMER_RESTART(tcp,
4522                                     tcp->tcp_fin_wait_2_flush_interval);
4523                         }
4524                         break;
4525                 case TCPS_FIN_WAIT_2:
4526                         break;  /* Shutdown hook? */
4527                 case TCPS_LAST_ACK:
4528                         freemsg(mp);
4529                         if (tcp->tcp_fin_acked) {
4530                                 (void) tcp_clean_death(tcp, 0);
4531                                 return;
4532                         }
4533                         goto xmit_check;
4534                 case TCPS_CLOSING:
4535                         if (tcp->tcp_fin_acked) {
4536                                 SET_TIME_WAIT(tcps, tcp, connp);
4537                                 DTRACE_TCP6(state__change, void, NULL,
4538                                     ip_xmit_attr_t *, connp->conn_ixa, void,
4539                                     NULL, tcp_t *, tcp, void, NULL, int32_t,
4540                                     TCPS_CLOSING);
4541                         }
4542                         /*FALLTHRU*/
4543                 case TCPS_CLOSE_WAIT:
4544                         freemsg(mp);
4545                         goto xmit_check;
4546                 default:
4547                         ASSERT(tcp->tcp_state != TCPS_TIME_WAIT);
4548                         break;
4549                 }
4550         }
4551         if (flags & TH_FIN) {
4552                 /* Make sure we ack the fin */
4553                 flags |= TH_ACK_NEEDED;
4554                 if (!tcp->tcp_fin_rcvd) {
4555                         tcp->tcp_fin_rcvd = B_TRUE;
4556                         tcp->tcp_rnxt++;
4557                         tcpha = tcp->tcp_tcpha;
4558                         tcpha->tha_ack = htonl(tcp->tcp_rnxt);
4559 
4560                         /*
4561                          * Generate the ordrel_ind at the end unless the
4562                          * conn is detached or it is a STREAMS based eager.
4563                          * In the eager case we defer the notification until
4564                          * tcp_accept_finish has run.
4565                          */
4566                         if (!TCP_IS_DETACHED(tcp) && (IPCL_IS_NONSTR(connp) ||
4567                             (tcp->tcp_listener == NULL &&
4568                             !tcp->tcp_hard_binding)))
4569                                 flags |= TH_ORDREL_NEEDED;
4570                         switch (tcp->tcp_state) {
4571                         case TCPS_SYN_RCVD:
4572                                 tcp->tcp_state = TCPS_CLOSE_WAIT;
4573                                 DTRACE_TCP6(state__change, void, NULL,
4574                                     ip_xmit_attr_t *, connp->conn_ixa,
4575                                     void, NULL, tcp_t *, tcp, void, NULL,
4576                                     int32_t, TCPS_SYN_RCVD);
4577                                 /* Keepalive? */
4578                                 break;
4579                         case TCPS_ESTABLISHED:
4580                                 tcp->tcp_state = TCPS_CLOSE_WAIT;
4581                                 DTRACE_TCP6(state__change, void, NULL,
4582                                     ip_xmit_attr_t *, connp->conn_ixa,
4583                                     void, NULL, tcp_t *, tcp, void, NULL,
4584                                     int32_t, TCPS_ESTABLISHED);
4585                                 /* Keepalive? */
4586                                 break;
4587                         case TCPS_FIN_WAIT_1:
4588                                 if (!tcp->tcp_fin_acked) {
4589                                         tcp->tcp_state = TCPS_CLOSING;
4590                                         DTRACE_TCP6(state__change, void, NULL,
4591                                             ip_xmit_attr_t *, connp->conn_ixa,
4592                                             void, NULL, tcp_t *, tcp, void,
4593                                             NULL, int32_t, TCPS_FIN_WAIT_1);
4594                                         break;
4595                                 }
4596                                 /* FALLTHRU */
4597                         case TCPS_FIN_WAIT_2:
4598                                 SET_TIME_WAIT(tcps, tcp, connp);
4599                                 DTRACE_TCP6(state__change, void, NULL,
4600                                     ip_xmit_attr_t *, connp->conn_ixa, void,
4601                                     NULL, tcp_t *, tcp, void, NULL, int32_t,
4602                                     TCPS_FIN_WAIT_2);
4603                                 if (seg_len) {
4604                                         /*
4605                                          * implies data piggybacked on FIN.
4606                                          * break to handle data.
4607                                          */
4608                                         break;
4609                                 }
4610                                 freemsg(mp);
4611                                 goto ack_check;
4612                         }
4613                 }
4614         }
4615         if (mp == NULL)
4616                 goto xmit_check;
4617         if (seg_len == 0) {
4618                 freemsg(mp);
4619                 goto xmit_check;
4620         }
4621         if (mp->b_rptr == mp->b_wptr) {
4622                 /*
4623                  * The header has been consumed, so we remove the
4624                  * zero-length mblk here.
4625                  */
4626                 mp1 = mp;
4627                 mp = mp->b_cont;
4628                 freeb(mp1);
4629         }
4630 update_ack:
4631         tcpha = tcp->tcp_tcpha;
4632         tcp->tcp_rack_cnt++;
4633         {
4634                 uint32_t cur_max;
4635 
4636                 cur_max = tcp->tcp_rack_cur_max;
4637                 if (tcp->tcp_rack_cnt >= cur_max) {
4638                         /*
4639                          * We have more unacked data than we should - send
4640                          * an ACK now.
4641                          */
4642                         flags |= TH_ACK_NEEDED;
4643                         cur_max++;
4644                         if (cur_max > tcp->tcp_rack_abs_max)
4645                                 tcp->tcp_rack_cur_max = tcp->tcp_rack_abs_max;
4646                         else
4647                                 tcp->tcp_rack_cur_max = cur_max;
4648                 } else if (TCP_IS_DETACHED(tcp)) {
4649                         /* We don't have an ACK timer for detached TCP. */
4650                         flags |= TH_ACK_NEEDED;
4651                 } else if (seg_len < mss) {
4652                         /*
4653                          * If we get a segment that is less than an mss, and we
4654                          * already have unacknowledged data, and the amount
4655                          * unacknowledged is not a multiple of mss, then we
4656                          * better generate an ACK now.  Otherwise, this may be
4657                          * the tail piece of a transaction, and we would rather
4658                          * wait for the response.
4659                          */
4660                         uint32_t udif;
4661                         ASSERT((uintptr_t)(tcp->tcp_rnxt - tcp->tcp_rack) <=
4662                             (uintptr_t)INT_MAX);
4663                         udif = (int)(tcp->tcp_rnxt - tcp->tcp_rack);
4664                         if (udif && (udif % mss))
4665                                 flags |= TH_ACK_NEEDED;
4666                         else
4667                                 flags |= TH_ACK_TIMER_NEEDED;
4668                 } else {
4669                         /* Start delayed ack timer */
4670                         flags |= TH_ACK_TIMER_NEEDED;
4671                 }
4672         }
4673         tcp->tcp_rnxt += seg_len;
4674         tcpha->tha_ack = htonl(tcp->tcp_rnxt);
4675 
4676         if (mp == NULL)
4677                 goto xmit_check;
4678 
4679         /* Update SACK list */
4680         if (tcp->tcp_snd_sack_ok && tcp->tcp_num_sack_blk > 0) {
4681                 tcp_sack_remove(tcp->tcp_sack_list, tcp->tcp_rnxt,
4682                     &(tcp->tcp_num_sack_blk));
4683         }
4684 
4685         if (tcp->tcp_urp_mp) {
4686                 tcp->tcp_urp_mp->b_cont = mp;
4687                 mp = tcp->tcp_urp_mp;
4688                 tcp->tcp_urp_mp = NULL;
4689                 /* Ready for a new signal. */
4690                 tcp->tcp_urp_last_valid = B_FALSE;
4691 #ifdef DEBUG
4692                 (void) strlog(TCP_MOD_ID, 0, 1, SL_TRACE,
4693                     "tcp_rput: sending exdata_ind %s",
4694                     tcp_display(tcp, NULL, DISP_PORT_ONLY));
4695 #endif /* DEBUG */
4696         }
4697 
4698         /*
4699          * Check for ancillary data changes compared to last segment.
4700          */
4701         if (connp->conn_recv_ancillary.crb_all != 0) {
4702                 mp = tcp_input_add_ancillary(tcp, mp, &ipp, ira);
4703                 if (mp == NULL)
4704                         return;
4705         }
4706 
4707         if (IPCL_IS_NONSTR(connp)) {
4708                 /*
4709                  * Non-STREAMS socket
4710                  */
4711                 boolean_t push = flags & (TH_PUSH|TH_FIN);
4712                 int error;
4713 
4714                 if ((*sockupcalls->su_recv)(connp->conn_upper_handle,
4715                     mp, seg_len, 0, &error, &push) <= 0) {
4716                         /*
4717                          * We should never be in middle of a
4718                          * fallback, the squeue guarantees that.
4719                          */
4720                         ASSERT(error != EOPNOTSUPP);
4721                         if (error == ENOSPC)
4722                                 tcp->tcp_rwnd -= seg_len;
4723                 } else if (push) {
4724                         /* PUSH bit set and sockfs is not flow controlled */
4725                         flags |= tcp_rwnd_reopen(tcp);
4726                 }
4727         } else if (tcp->tcp_listener != NULL || tcp->tcp_hard_binding) {
4728                 /*
4729                  * Side queue inbound data until the accept happens.
4730                  * tcp_accept/tcp_rput drains this when the accept happens.
4731                  * M_DATA is queued on b_cont. Otherwise (T_OPTDATA_IND or
4732                  * T_EXDATA_IND) it is queued on b_next.
4733                  * XXX Make urgent data use this. Requires:
4734                  *      Removing tcp_listener check for TH_URG
4735                  *      Making M_PCPROTO and MARK messages skip the eager case
4736                  */
4737 
4738                 tcp_rcv_enqueue(tcp, mp, seg_len, ira->ira_cred);
4739         } else {
4740                 /* Active STREAMS socket */
4741                 if (mp->b_datap->db_type != M_DATA ||
4742                     (flags & TH_MARKNEXT_NEEDED)) {
4743                         if (tcp->tcp_rcv_list != NULL) {
4744                                 flags |= tcp_rcv_drain(tcp);
4745                         }
4746                         ASSERT(tcp->tcp_rcv_list == NULL ||
4747                             tcp->tcp_fused_sigurg);
4748 
4749                         if (flags & TH_MARKNEXT_NEEDED) {
4750 #ifdef DEBUG
4751                                 (void) strlog(TCP_MOD_ID, 0, 1, SL_TRACE,
4752                                     "tcp_rput: sending MSGMARKNEXT %s",
4753                                     tcp_display(tcp, NULL,
4754                                     DISP_PORT_ONLY));
4755 #endif /* DEBUG */
4756                                 mp->b_flag |= MSGMARKNEXT;
4757                                 flags &= ~TH_MARKNEXT_NEEDED;
4758                         }
4759 
4760                         if (is_system_labeled())
4761                                 tcp_setcred_data(mp, ira);
4762 
4763                         putnext(connp->conn_rq, mp);
4764                         if (!canputnext(connp->conn_rq))
4765                                 tcp->tcp_rwnd -= seg_len;
4766                 } else if ((flags & (TH_PUSH|TH_FIN)) ||
4767                     tcp->tcp_rcv_cnt + seg_len >= connp->conn_rcvbuf >> 3) {
4768                         if (tcp->tcp_rcv_list != NULL) {
4769                                 /*
4770                                  * Enqueue the new segment first and then
4771                                  * call tcp_rcv_drain() to send all data
4772                                  * up.  The other way to do this is to
4773                                  * send all queued data up and then call
4774                                  * putnext() to send the new segment up.
4775                                  * This way can remove the else part later
4776                                  * on.
4777                                  *
4778                                  * We don't do this to avoid one more call to
4779                                  * canputnext() as tcp_rcv_drain() needs to
4780                                  * call canputnext().
4781                                  */
4782                                 tcp_rcv_enqueue(tcp, mp, seg_len,
4783                                     ira->ira_cred);
4784                                 flags |= tcp_rcv_drain(tcp);
4785                         } else {
4786                                 if (is_system_labeled())
4787                                         tcp_setcred_data(mp, ira);
4788 
4789                                 putnext(connp->conn_rq, mp);
4790                                 if (!canputnext(connp->conn_rq))
4791                                         tcp->tcp_rwnd -= seg_len;
4792                         }
4793                 } else {
4794                         /*
4795                          * Enqueue all packets when processing an mblk
4796                          * from the co queue and also enqueue normal packets.
4797                          */
4798                         tcp_rcv_enqueue(tcp, mp, seg_len, ira->ira_cred);
4799                 }
4800                 /*
4801                  * Make sure the timer is running if we have data waiting
4802                  * for a push bit. This provides resiliency against
4803                  * implementations that do not correctly generate push bits.
4804                  */
4805                 if (tcp->tcp_rcv_list != NULL && tcp->tcp_push_tid == 0) {
4806                         /*
4807                          * The connection may be closed at this point, so don't
4808                          * do anything for a detached tcp.
4809                          */
4810                         if (!TCP_IS_DETACHED(tcp))
4811                                 tcp->tcp_push_tid = TCP_TIMER(tcp,
4812                                     tcp_push_timer,
4813                                     tcps->tcps_push_timer_interval);
4814                 }
4815         }
4816 
4817 xmit_check:
4818         /* Is there anything left to do? */
4819         ASSERT(!(flags & TH_MARKNEXT_NEEDED));
4820         if ((flags & (TH_REXMIT_NEEDED|TH_XMIT_NEEDED|TH_ACK_NEEDED|
4821             TH_NEED_SACK_REXMIT|TH_LIMIT_XMIT|TH_ACK_TIMER_NEEDED|
4822             TH_ORDREL_NEEDED|TH_SEND_URP_MARK)) == 0)
4823                 goto done;
4824 
4825         /* Any transmit work to do and a non-zero window? */
4826         if ((flags & (TH_REXMIT_NEEDED|TH_XMIT_NEEDED|TH_NEED_SACK_REXMIT|
4827             TH_LIMIT_XMIT)) && tcp->tcp_swnd != 0) {
4828                 if (flags & TH_REXMIT_NEEDED) {
4829                         uint32_t snd_size = tcp->tcp_snxt - tcp->tcp_suna;
4830 
4831                         TCPS_BUMP_MIB(tcps, tcpOutFastRetrans);
4832                         if (snd_size > mss)
4833                                 snd_size = mss;
4834                         if (snd_size > tcp->tcp_swnd)
4835                                 snd_size = tcp->tcp_swnd;
4836                         mp1 = tcp_xmit_mp(tcp, tcp->tcp_xmit_head, snd_size,
4837                             NULL, NULL, tcp->tcp_suna, B_TRUE, &snd_size,
4838                             B_TRUE);
4839 
4840                         if (mp1 != NULL) {
4841                                 tcp->tcp_xmit_head->b_prev =
4842                                     (mblk_t *)LBOLT_FASTPATH;
4843                                 tcp->tcp_csuna = tcp->tcp_snxt;
4844                                 TCPS_BUMP_MIB(tcps, tcpRetransSegs);
4845                                 TCPS_UPDATE_MIB(tcps, tcpRetransBytes,
4846                                     snd_size);
4847                                 tcp_send_data(tcp, mp1);
4848                         }
4849                 }
4850                 if (flags & TH_NEED_SACK_REXMIT) {
4851                         tcp_sack_rexmit(tcp, &flags);
4852                 }
4853                 /*
4854                  * For TH_LIMIT_XMIT, tcp_wput_data() is called to send
4855                  * out new segment.  Note that tcp_rexmit should not be
4856                  * set, otherwise TH_LIMIT_XMIT should not be set.
4857                  */
4858                 if (flags & (TH_XMIT_NEEDED|TH_LIMIT_XMIT)) {
4859                         if (!tcp->tcp_rexmit) {
4860                                 tcp_wput_data(tcp, NULL, B_FALSE);
4861                         } else {
4862                                 tcp_ss_rexmit(tcp);
4863                         }
4864                 }
4865                 /*
4866                  * Adjust tcp_cwnd back to normal value after sending
4867                  * new data segments.
4868                  */
4869                 if (flags & TH_LIMIT_XMIT) {
4870                         tcp->tcp_cwnd -= mss << (tcp->tcp_dupack_cnt - 1);
4871                         /*
4872                          * This will restart the timer.  Restarting the
4873                          * timer is used to avoid a timeout before the
4874                          * limited transmitted segment's ACK gets back.
4875                          */
4876                         if (tcp->tcp_xmit_head != NULL)
4877                                 tcp->tcp_xmit_head->b_prev =
4878                                     (mblk_t *)LBOLT_FASTPATH;
4879                 }
4880 
4881                 /* Anything more to do? */
4882                 if ((flags & (TH_ACK_NEEDED|TH_ACK_TIMER_NEEDED|
4883                     TH_ORDREL_NEEDED|TH_SEND_URP_MARK)) == 0)
4884                         goto done;
4885         }
4886 ack_check:
4887         if (flags & TH_SEND_URP_MARK) {
4888                 ASSERT(tcp->tcp_urp_mark_mp);
4889                 ASSERT(!IPCL_IS_NONSTR(connp));
4890                 /*
4891                  * Send up any queued data and then send the mark message
4892                  */
4893                 if (tcp->tcp_rcv_list != NULL) {
4894                         flags |= tcp_rcv_drain(tcp);
4895 
4896                 }
4897                 ASSERT(tcp->tcp_rcv_list == NULL || tcp->tcp_fused_sigurg);
4898                 mp1 = tcp->tcp_urp_mark_mp;
4899                 tcp->tcp_urp_mark_mp = NULL;
4900                 if (is_system_labeled())
4901                         tcp_setcred_data(mp1, ira);
4902 
4903                 putnext(connp->conn_rq, mp1);
4904 #ifdef DEBUG
4905                 (void) strlog(TCP_MOD_ID, 0, 1, SL_TRACE,
4906                     "tcp_rput: sending zero-length %s %s",
4907                     ((mp1->b_flag & MSGMARKNEXT) ? "MSGMARKNEXT" :
4908                     "MSGNOTMARKNEXT"),
4909                     tcp_display(tcp, NULL, DISP_PORT_ONLY));
4910 #endif /* DEBUG */
4911                 flags &= ~TH_SEND_URP_MARK;
4912         }
4913         if (flags & TH_ACK_NEEDED) {
4914                 /*
4915                  * Time to send an ack for some reason.
4916                  */
4917                 mp1 = tcp_ack_mp(tcp);
4918 
4919                 if (mp1 != NULL) {
4920                         tcp_send_data(tcp, mp1);
4921                         BUMP_LOCAL(tcp->tcp_obsegs);
4922                         TCPS_BUMP_MIB(tcps, tcpOutAck);
4923                 }
4924                 if (tcp->tcp_ack_tid != 0) {
4925                         (void) TCP_TIMER_CANCEL(tcp, tcp->tcp_ack_tid);
4926                         tcp->tcp_ack_tid = 0;
4927                 }
4928         }
4929         if (flags & TH_ACK_TIMER_NEEDED) {
4930                 /*
4931                  * Arrange for deferred ACK or push wait timeout.
4932                  * Start timer if it is not already running.
4933                  */
4934                 if (tcp->tcp_ack_tid == 0) {
4935                         tcp->tcp_ack_tid = TCP_TIMER(tcp, tcp_ack_timer,
4936                             tcp->tcp_localnet ?
4937                             tcps->tcps_local_dack_interval :
4938                             tcps->tcps_deferred_ack_interval);
4939                 }
4940         }
4941         if (flags & TH_ORDREL_NEEDED) {
4942                 /*
4943                  * Notify upper layer about an orderly release. If this is
4944                  * a non-STREAMS socket, then just make an upcall. For STREAMS
4945                  * we send up an ordrel_ind, unless this is an eager, in which
4946                  * case the ordrel will be sent when tcp_accept_finish runs.
4947                  * Note that for non-STREAMS we make an upcall even if it is an
4948                  * eager, because we have an upper handle to send it to.
4949                  */
4950                 ASSERT(IPCL_IS_NONSTR(connp) || tcp->tcp_listener == NULL);
4951                 ASSERT(!tcp->tcp_detached);
4952 
4953                 if (IPCL_IS_NONSTR(connp)) {
4954                         ASSERT(tcp->tcp_ordrel_mp == NULL);
4955                         tcp->tcp_ordrel_done = B_TRUE;
4956                         (*sockupcalls->su_opctl)(connp->conn_upper_handle,
4957                             SOCK_OPCTL_SHUT_RECV, 0);
4958                         goto done;
4959                 }
4960 
4961                 if (tcp->tcp_rcv_list != NULL) {
4962                         /*
4963                          * Push any mblk(s) enqueued from co processing.
4964                          */
4965                         flags |= tcp_rcv_drain(tcp);
4966                 }
4967                 ASSERT(tcp->tcp_rcv_list == NULL || tcp->tcp_fused_sigurg);
4968 
4969                 mp1 = tcp->tcp_ordrel_mp;
4970                 tcp->tcp_ordrel_mp = NULL;
4971                 tcp->tcp_ordrel_done = B_TRUE;
4972                 putnext(connp->conn_rq, mp1);
4973         }
4974 done:
4975         ASSERT(!(flags & TH_MARKNEXT_NEEDED));
4976 }
4977 
4978 /*
4979  * Attach ancillary data to a received TCP segments for the
4980  * ancillary pieces requested by the application that are
4981  * different than they were in the previous data segment.
4982  *
4983  * Save the "current" values once memory allocation is ok so that
4984  * when memory allocation fails we can just wait for the next data segment.
4985  */
4986 static mblk_t *
4987 tcp_input_add_ancillary(tcp_t *tcp, mblk_t *mp, ip_pkt_t *ipp,
4988     ip_recv_attr_t *ira)
4989 {
4990         struct T_optdata_ind *todi;
4991         int optlen;
4992         uchar_t *optptr;
4993         struct T_opthdr *toh;
4994         crb_t addflag;  /* Which pieces to add */
4995         mblk_t *mp1;
4996         conn_t  *connp = tcp->tcp_connp;
4997 
4998         optlen = 0;
4999         addflag.crb_all = 0;
5000         /* If app asked for pktinfo and the index has changed ... */
5001         if (connp->conn_recv_ancillary.crb_ip_recvpktinfo &&
5002             ira->ira_ruifindex != tcp->tcp_recvifindex) {
5003                 optlen += sizeof (struct T_opthdr) +
5004                     sizeof (struct in6_pktinfo);
5005                 addflag.crb_ip_recvpktinfo = 1;
5006         }
5007         /* If app asked for hoplimit and it has changed ... */
5008         if (connp->conn_recv_ancillary.crb_ipv6_recvhoplimit &&
5009             ipp->ipp_hoplimit != tcp->tcp_recvhops) {
5010                 optlen += sizeof (struct T_opthdr) + sizeof (uint_t);
5011                 addflag.crb_ipv6_recvhoplimit = 1;
5012         }
5013         /* If app asked for tclass and it has changed ... */
5014         if (connp->conn_recv_ancillary.crb_ipv6_recvtclass &&
5015             ipp->ipp_tclass != tcp->tcp_recvtclass) {
5016                 optlen += sizeof (struct T_opthdr) + sizeof (uint_t);
5017                 addflag.crb_ipv6_recvtclass = 1;
5018         }
5019         /*
5020          * If app asked for hopbyhop headers and it has changed ...
5021          * For security labels, note that (1) security labels can't change on
5022          * a connected socket at all, (2) we're connected to at most one peer,
5023          * (3) if anything changes, then it must be some other extra option.
5024          */
5025         if (connp->conn_recv_ancillary.crb_ipv6_recvhopopts &&
5026             ip_cmpbuf(tcp->tcp_hopopts, tcp->tcp_hopoptslen,
5027             (ipp->ipp_fields & IPPF_HOPOPTS),
5028             ipp->ipp_hopopts, ipp->ipp_hopoptslen)) {
5029                 optlen += sizeof (struct T_opthdr) + ipp->ipp_hopoptslen;
5030                 addflag.crb_ipv6_recvhopopts = 1;
5031                 if (!ip_allocbuf((void **)&tcp->tcp_hopopts,
5032                     &tcp->tcp_hopoptslen, (ipp->ipp_fields & IPPF_HOPOPTS),
5033                     ipp->ipp_hopopts, ipp->ipp_hopoptslen))
5034                         return (mp);
5035         }
5036         /* If app asked for dst headers before routing headers ... */
5037         if (connp->conn_recv_ancillary.crb_ipv6_recvrthdrdstopts &&
5038             ip_cmpbuf(tcp->tcp_rthdrdstopts, tcp->tcp_rthdrdstoptslen,
5039             (ipp->ipp_fields & IPPF_RTHDRDSTOPTS),
5040             ipp->ipp_rthdrdstopts, ipp->ipp_rthdrdstoptslen)) {
5041                 optlen += sizeof (struct T_opthdr) +
5042                     ipp->ipp_rthdrdstoptslen;
5043                 addflag.crb_ipv6_recvrthdrdstopts = 1;
5044                 if (!ip_allocbuf((void **)&tcp->tcp_rthdrdstopts,
5045                     &tcp->tcp_rthdrdstoptslen,
5046                     (ipp->ipp_fields & IPPF_RTHDRDSTOPTS),
5047                     ipp->ipp_rthdrdstopts, ipp->ipp_rthdrdstoptslen))
5048                         return (mp);
5049         }
5050         /* If app asked for routing headers and it has changed ... */
5051         if (connp->conn_recv_ancillary.crb_ipv6_recvrthdr &&
5052             ip_cmpbuf(tcp->tcp_rthdr, tcp->tcp_rthdrlen,
5053             (ipp->ipp_fields & IPPF_RTHDR),
5054             ipp->ipp_rthdr, ipp->ipp_rthdrlen)) {
5055                 optlen += sizeof (struct T_opthdr) + ipp->ipp_rthdrlen;
5056                 addflag.crb_ipv6_recvrthdr = 1;
5057                 if (!ip_allocbuf((void **)&tcp->tcp_rthdr,
5058                     &tcp->tcp_rthdrlen, (ipp->ipp_fields & IPPF_RTHDR),
5059                     ipp->ipp_rthdr, ipp->ipp_rthdrlen))
5060                         return (mp);
5061         }
5062         /* If app asked for dest headers and it has changed ... */
5063         if ((connp->conn_recv_ancillary.crb_ipv6_recvdstopts ||
5064             connp->conn_recv_ancillary.crb_old_ipv6_recvdstopts) &&
5065             ip_cmpbuf(tcp->tcp_dstopts, tcp->tcp_dstoptslen,
5066             (ipp->ipp_fields & IPPF_DSTOPTS),
5067             ipp->ipp_dstopts, ipp->ipp_dstoptslen)) {
5068                 optlen += sizeof (struct T_opthdr) + ipp->ipp_dstoptslen;
5069                 addflag.crb_ipv6_recvdstopts = 1;
5070                 if (!ip_allocbuf((void **)&tcp->tcp_dstopts,
5071                     &tcp->tcp_dstoptslen, (ipp->ipp_fields & IPPF_DSTOPTS),
5072                     ipp->ipp_dstopts, ipp->ipp_dstoptslen))
5073                         return (mp);
5074         }
5075 
5076         if (optlen == 0) {
5077                 /* Nothing to add */
5078                 return (mp);
5079         }
5080         mp1 = allocb(sizeof (struct T_optdata_ind) + optlen, BPRI_MED);
5081         if (mp1 == NULL) {
5082                 /*
5083                  * Defer sending ancillary data until the next TCP segment
5084                  * arrives.
5085                  */
5086                 return (mp);
5087         }
5088         mp1->b_cont = mp;
5089         mp = mp1;
5090         mp->b_wptr += sizeof (*todi) + optlen;
5091         mp->b_datap->db_type = M_PROTO;
5092         todi = (struct T_optdata_ind *)mp->b_rptr;
5093         todi->PRIM_type = T_OPTDATA_IND;
5094         todi->DATA_flag = 1; /* MORE data */
5095         todi->OPT_length = optlen;
5096         todi->OPT_offset = sizeof (*todi);
5097         optptr = (uchar_t *)&todi[1];
5098         /*
5099          * If app asked for pktinfo and the index has changed ...
5100          * Note that the local address never changes for the connection.
5101          */
5102         if (addflag.crb_ip_recvpktinfo) {
5103                 struct in6_pktinfo *pkti;
5104                 uint_t ifindex;
5105 
5106                 ifindex = ira->ira_ruifindex;
5107                 toh = (struct T_opthdr *)optptr;
5108                 toh->level = IPPROTO_IPV6;
5109                 toh->name = IPV6_PKTINFO;
5110                 toh->len = sizeof (*toh) + sizeof (*pkti);
5111                 toh->status = 0;
5112                 optptr += sizeof (*toh);
5113                 pkti = (struct in6_pktinfo *)optptr;
5114                 pkti->ipi6_addr = connp->conn_laddr_v6;
5115                 pkti->ipi6_ifindex = ifindex;
5116                 optptr += sizeof (*pkti);
5117                 ASSERT(OK_32PTR(optptr));
5118                 /* Save as "last" value */
5119                 tcp->tcp_recvifindex = ifindex;
5120         }
5121         /* If app asked for hoplimit and it has changed ... */
5122         if (addflag.crb_ipv6_recvhoplimit) {
5123                 toh = (struct T_opthdr *)optptr;
5124                 toh->level = IPPROTO_IPV6;
5125                 toh->name = IPV6_HOPLIMIT;
5126                 toh->len = sizeof (*toh) + sizeof (uint_t);
5127                 toh->status = 0;
5128                 optptr += sizeof (*toh);
5129                 *(uint_t *)optptr = ipp->ipp_hoplimit;
5130                 optptr += sizeof (uint_t);
5131                 ASSERT(OK_32PTR(optptr));
5132                 /* Save as "last" value */
5133                 tcp->tcp_recvhops = ipp->ipp_hoplimit;
5134         }
5135         /* If app asked for tclass and it has changed ... */
5136         if (addflag.crb_ipv6_recvtclass) {
5137                 toh = (struct T_opthdr *)optptr;
5138                 toh->level = IPPROTO_IPV6;
5139                 toh->name = IPV6_TCLASS;
5140                 toh->len = sizeof (*toh) + sizeof (uint_t);
5141                 toh->status = 0;
5142                 optptr += sizeof (*toh);
5143                 *(uint_t *)optptr = ipp->ipp_tclass;
5144                 optptr += sizeof (uint_t);
5145                 ASSERT(OK_32PTR(optptr));
5146                 /* Save as "last" value */
5147                 tcp->tcp_recvtclass = ipp->ipp_tclass;
5148         }
5149         if (addflag.crb_ipv6_recvhopopts) {
5150                 toh = (struct T_opthdr *)optptr;
5151                 toh->level = IPPROTO_IPV6;
5152                 toh->name = IPV6_HOPOPTS;
5153                 toh->len = sizeof (*toh) + ipp->ipp_hopoptslen;
5154                 toh->status = 0;
5155                 optptr += sizeof (*toh);
5156                 bcopy((uchar_t *)ipp->ipp_hopopts, optptr, ipp->ipp_hopoptslen);
5157                 optptr += ipp->ipp_hopoptslen;
5158                 ASSERT(OK_32PTR(optptr));
5159                 /* Save as last value */
5160                 ip_savebuf((void **)&tcp->tcp_hopopts, &tcp->tcp_hopoptslen,
5161                     (ipp->ipp_fields & IPPF_HOPOPTS),
5162                     ipp->ipp_hopopts, ipp->ipp_hopoptslen);
5163         }
5164         if (addflag.crb_ipv6_recvrthdrdstopts) {
5165                 toh = (struct T_opthdr *)optptr;
5166                 toh->level = IPPROTO_IPV6;
5167                 toh->name = IPV6_RTHDRDSTOPTS;
5168                 toh->len = sizeof (*toh) + ipp->ipp_rthdrdstoptslen;
5169                 toh->status = 0;
5170                 optptr += sizeof (*toh);
5171                 bcopy(ipp->ipp_rthdrdstopts, optptr, ipp->ipp_rthdrdstoptslen);
5172                 optptr += ipp->ipp_rthdrdstoptslen;
5173                 ASSERT(OK_32PTR(optptr));
5174                 /* Save as last value */
5175                 ip_savebuf((void **)&tcp->tcp_rthdrdstopts,
5176                     &tcp->tcp_rthdrdstoptslen,
5177                     (ipp->ipp_fields & IPPF_RTHDRDSTOPTS),
5178                     ipp->ipp_rthdrdstopts, ipp->ipp_rthdrdstoptslen);
5179         }
5180         if (addflag.crb_ipv6_recvrthdr) {
5181                 toh = (struct T_opthdr *)optptr;
5182                 toh->level = IPPROTO_IPV6;
5183                 toh->name = IPV6_RTHDR;
5184                 toh->len = sizeof (*toh) + ipp->ipp_rthdrlen;
5185                 toh->status = 0;
5186                 optptr += sizeof (*toh);
5187                 bcopy(ipp->ipp_rthdr, optptr, ipp->ipp_rthdrlen);
5188                 optptr += ipp->ipp_rthdrlen;
5189                 ASSERT(OK_32PTR(optptr));
5190                 /* Save as last value */
5191                 ip_savebuf((void **)&tcp->tcp_rthdr, &tcp->tcp_rthdrlen,
5192                     (ipp->ipp_fields & IPPF_RTHDR),
5193                     ipp->ipp_rthdr, ipp->ipp_rthdrlen);
5194         }
5195         if (addflag.crb_ipv6_recvdstopts) {
5196                 toh = (struct T_opthdr *)optptr;
5197                 toh->level = IPPROTO_IPV6;
5198                 toh->name = IPV6_DSTOPTS;
5199                 toh->len = sizeof (*toh) + ipp->ipp_dstoptslen;
5200                 toh->status = 0;
5201                 optptr += sizeof (*toh);
5202                 bcopy(ipp->ipp_dstopts, optptr, ipp->ipp_dstoptslen);
5203                 optptr += ipp->ipp_dstoptslen;
5204                 ASSERT(OK_32PTR(optptr));
5205                 /* Save as last value */
5206                 ip_savebuf((void **)&tcp->tcp_dstopts, &tcp->tcp_dstoptslen,
5207                     (ipp->ipp_fields & IPPF_DSTOPTS),
5208                     ipp->ipp_dstopts, ipp->ipp_dstoptslen);
5209         }
5210         ASSERT(optptr == mp->b_wptr);
5211         return (mp);
5212 }
5213 
5214 /* The minimum of smoothed mean deviation in RTO calculation. */
5215 #define TCP_SD_MIN      400
5216 
5217 /*
5218  * Set RTO for this connection.  The formula is from Jacobson and Karels'
5219  * "Congestion Avoidance and Control" in SIGCOMM '88.  The variable names
5220  * are the same as those in Appendix A.2 of that paper.
5221  *
5222  * m = new measurement
5223  * sa = smoothed RTT average (8 * average estimates).
5224  * sv = smoothed mean deviation (mdev) of RTT (4 * deviation estimates).
5225  */
5226 static void
5227 tcp_set_rto(tcp_t *tcp, clock_t rtt)
5228 {
5229         long m = TICK_TO_MSEC(rtt);
5230         clock_t sa = tcp->tcp_rtt_sa;
5231         clock_t sv = tcp->tcp_rtt_sd;
5232         clock_t rto;
5233         tcp_stack_t     *tcps = tcp->tcp_tcps;
5234 
5235         TCPS_BUMP_MIB(tcps, tcpRttUpdate);
5236         tcp->tcp_rtt_update++;
5237 
5238         /* tcp_rtt_sa is not 0 means this is a new sample. */
5239         if (sa != 0) {
5240                 /*
5241                  * Update average estimator:
5242                  *      new rtt = 7/8 old rtt + 1/8 Error
5243                  */
5244 
5245                 /* m is now Error in estimate. */
5246                 m -= sa >> 3;
5247                 if ((sa += m) <= 0) {
5248                         /*
5249                          * Don't allow the smoothed average to be negative.
5250                          * We use 0 to denote reinitialization of the
5251                          * variables.
5252                          */
5253                         sa = 1;
5254                 }
5255 
5256                 /*
5257                  * Update deviation estimator:
5258                  *      new mdev = 3/4 old mdev + 1/4 (abs(Error) - old mdev)
5259                  */
5260                 if (m < 0)
5261                         m = -m;
5262                 m -= sv >> 2;
5263                 sv += m;
5264         } else {
5265                 /*
5266                  * This follows BSD's implementation.  So the reinitialized
5267                  * RTO is 3 * m.  We cannot go less than 2 because if the
5268                  * link is bandwidth dominated, doubling the window size
5269                  * during slow start means doubling the RTT.  We want to be
5270                  * more conservative when we reinitialize our estimates.  3
5271                  * is just a convenient number.
5272                  */
5273                 sa = m << 3;
5274                 sv = m << 1;
5275         }
5276         if (sv < TCP_SD_MIN) {
5277                 /*
5278                  * We do not know that if sa captures the delay ACK
5279                  * effect as in a long train of segments, a receiver
5280                  * does not delay its ACKs.  So set the minimum of sv
5281                  * to be TCP_SD_MIN, which is default to 400 ms, twice
5282                  * of BSD DATO.  That means the minimum of mean
5283                  * deviation is 100 ms.
5284                  *
5285                  */
5286                 sv = TCP_SD_MIN;
5287         }
5288         tcp->tcp_rtt_sa = sa;
5289         tcp->tcp_rtt_sd = sv;
5290         /*
5291          * RTO = average estimates (sa / 8) + 4 * deviation estimates (sv)
5292          *
5293          * Add tcp_rexmit_interval extra in case of extreme environment
5294          * where the algorithm fails to work.  The default value of
5295          * tcp_rexmit_interval_extra should be 0.
5296          *
5297          * As we use a finer grained clock than BSD and update
5298          * RTO for every ACKs, add in another .25 of RTT to the
5299          * deviation of RTO to accomodate burstiness of 1/4 of
5300          * window size.
5301          */
5302         rto = (sa >> 3) + sv + tcps->tcps_rexmit_interval_extra + (sa >> 5);
5303 
5304         TCP_SET_RTO(tcp, rto);
5305 
5306         /* Now, we can reset tcp_timer_backoff to use the new RTO... */
5307         tcp->tcp_timer_backoff = 0;
5308 }
5309 
5310 /*
5311  * On a labeled system we have some protocols above TCP, such as RPC, which
5312  * appear to assume that every mblk in a chain has a db_credp.
5313  */
5314 static void
5315 tcp_setcred_data(mblk_t *mp, ip_recv_attr_t *ira)
5316 {
5317         ASSERT(is_system_labeled());
5318         ASSERT(ira->ira_cred != NULL);
5319 
5320         while (mp != NULL) {
5321                 mblk_setcred(mp, ira->ira_cred, NOPID);
5322                 mp = mp->b_cont;
5323         }
5324 }
5325 
5326 uint_t
5327 tcp_rwnd_reopen(tcp_t *tcp)
5328 {
5329         uint_t ret = 0;
5330         uint_t thwin;
5331         conn_t *connp = tcp->tcp_connp;
5332 
5333         /* Learn the latest rwnd information that we sent to the other side. */
5334         thwin = ((uint_t)ntohs(tcp->tcp_tcpha->tha_win))
5335             << tcp->tcp_rcv_ws;
5336         /* This is peer's calculated send window (our receive window). */
5337         thwin -= tcp->tcp_rnxt - tcp->tcp_rack;
5338         /*
5339          * Increase the receive window to max.  But we need to do receiver
5340          * SWS avoidance.  This means that we need to check the increase of
5341          * of receive window is at least 1 MSS.
5342          */
5343         if (connp->conn_rcvbuf - thwin >= tcp->tcp_mss) {
5344                 /*
5345                  * If the window that the other side knows is less than max
5346                  * deferred acks segments, send an update immediately.
5347                  */
5348                 if (thwin < tcp->tcp_rack_cur_max * tcp->tcp_mss) {
5349                         TCPS_BUMP_MIB(tcp->tcp_tcps, tcpOutWinUpdate);
5350                         ret = TH_ACK_NEEDED;
5351                 }
5352                 tcp->tcp_rwnd = connp->conn_rcvbuf;
5353         }
5354         return (ret);
5355 }
5356 
5357 /*
5358  * Handle a packet that has been reclassified by TCP.
5359  * This function drops the ref on connp that the caller had.
5360  */
5361 void
5362 tcp_reinput(conn_t *connp, mblk_t *mp, ip_recv_attr_t *ira, ip_stack_t *ipst)
5363 {
5364         ipsec_stack_t   *ipss = ipst->ips_netstack->netstack_ipsec;
5365 
5366         if (connp->conn_incoming_ifindex != 0 &&
5367             connp->conn_incoming_ifindex != ira->ira_ruifindex) {
5368                 freemsg(mp);
5369                 CONN_DEC_REF(connp);
5370                 return;
5371         }
5372 
5373         if (CONN_INBOUND_POLICY_PRESENT_V6(connp, ipss) ||
5374             (ira->ira_flags & IRAF_IPSEC_SECURE)) {
5375                 ip6_t *ip6h;
5376                 ipha_t *ipha;
5377 
5378                 if (ira->ira_flags & IRAF_IS_IPV4) {
5379                         ipha = (ipha_t *)mp->b_rptr;
5380                         ip6h = NULL;
5381                 } else {
5382                         ipha = NULL;
5383                         ip6h = (ip6_t *)mp->b_rptr;
5384                 }
5385                 mp = ipsec_check_inbound_policy(mp, connp, ipha, ip6h, ira);
5386                 if (mp == NULL) {
5387                         BUMP_MIB(&ipst->ips_ip_mib, ipIfStatsInDiscards);
5388                         /* Note that mp is NULL */
5389                         ip_drop_input("ipIfStatsInDiscards", mp, NULL);
5390                         CONN_DEC_REF(connp);
5391                         return;
5392                 }
5393         }
5394 
5395         if (IPCL_IS_TCP(connp)) {
5396                 /*
5397                  * do not drain, certain use cases can blow
5398                  * the stack
5399                  */
5400                 SQUEUE_ENTER_ONE(connp->conn_sqp, mp,
5401                     connp->conn_recv, connp, ira,
5402                     SQ_NODRAIN, SQTAG_IP_TCP_INPUT);
5403         } else {
5404                 /* Not TCP; must be SOCK_RAW, IPPROTO_TCP */
5405                 (connp->conn_recv)(connp, mp, NULL,
5406                     ira);
5407                 CONN_DEC_REF(connp);
5408         }
5409 
5410 }
5411 
5412 /* ARGSUSED */
5413 static void
5414 tcp_rsrv_input(void *arg, mblk_t *mp, void *arg2, ip_recv_attr_t *dummy)
5415 {
5416         conn_t  *connp = (conn_t *)arg;
5417         tcp_t   *tcp = connp->conn_tcp;
5418         queue_t *q = connp->conn_rq;
5419 
5420         ASSERT(!IPCL_IS_NONSTR(connp));
5421         mutex_enter(&tcp->tcp_rsrv_mp_lock);
5422         tcp->tcp_rsrv_mp = mp;
5423         mutex_exit(&tcp->tcp_rsrv_mp_lock);
5424 
5425         if (TCP_IS_DETACHED(tcp) || q == NULL) {
5426                 return;
5427         }
5428 
5429         if (tcp->tcp_fused) {
5430                 tcp_fuse_backenable(tcp);
5431                 return;
5432         }
5433 
5434         if (canputnext(q)) {
5435                 /* Not flow-controlled, open rwnd */
5436                 tcp->tcp_rwnd = connp->conn_rcvbuf;
5437 
5438                 /*
5439                  * Send back a window update immediately if TCP is above
5440                  * ESTABLISHED state and the increase of the rcv window
5441                  * that the other side knows is at least 1 MSS after flow
5442                  * control is lifted.
5443                  */
5444                 if (tcp->tcp_state >= TCPS_ESTABLISHED &&
5445                     tcp_rwnd_reopen(tcp) == TH_ACK_NEEDED) {
5446                         tcp_xmit_ctl(NULL, tcp,
5447                             (tcp->tcp_swnd == 0) ? tcp->tcp_suna :
5448                             tcp->tcp_snxt, tcp->tcp_rnxt, TH_ACK);
5449                 }
5450         }
5451 }
5452 
5453 /*
5454  * The read side service routine is called mostly when we get back-enabled as a
5455  * result of flow control relief.  Since we don't actually queue anything in
5456  * TCP, we have no data to send out of here.  What we do is clear the receive
5457  * window, and send out a window update.
5458  */
5459 int
5460 tcp_rsrv(queue_t *q)
5461 {
5462         conn_t          *connp = Q_TO_CONN(q);
5463         tcp_t           *tcp = connp->conn_tcp;
5464         mblk_t          *mp;
5465 
5466         /* No code does a putq on the read side */
5467         ASSERT(q->q_first == NULL);
5468 
5469         /*
5470          * If tcp->tcp_rsrv_mp == NULL, it means that tcp_rsrv() has already
5471          * been run.  So just return.
5472          */
5473         mutex_enter(&tcp->tcp_rsrv_mp_lock);
5474         if ((mp = tcp->tcp_rsrv_mp) == NULL) {
5475                 mutex_exit(&tcp->tcp_rsrv_mp_lock);
5476                 return (0);
5477         }
5478         tcp->tcp_rsrv_mp = NULL;
5479         mutex_exit(&tcp->tcp_rsrv_mp_lock);
5480 
5481         CONN_INC_REF(connp);
5482         SQUEUE_ENTER_ONE(connp->conn_sqp, mp, tcp_rsrv_input, connp,
5483             NULL, SQ_PROCESS, SQTAG_TCP_RSRV);
5484         return (0);
5485 }
5486 
5487 /* At minimum we need 8 bytes in the TCP header for the lookup */
5488 #define ICMP_MIN_TCP_HDR        8
5489 
5490 /*
5491  * tcp_icmp_input is called as conn_recvicmp to process ICMP error messages
5492  * passed up by IP. The message is always received on the correct tcp_t.
5493  * Assumes that IP has pulled up everything up to and including the ICMP header.
5494  */
5495 /* ARGSUSED2 */
5496 void
5497 tcp_icmp_input(void *arg1, mblk_t *mp, void *arg2, ip_recv_attr_t *ira)
5498 {
5499         conn_t          *connp = (conn_t *)arg1;
5500         icmph_t         *icmph;
5501         ipha_t          *ipha;
5502         int             iph_hdr_length;
5503         tcpha_t         *tcpha;
5504         uint32_t        seg_seq;
5505         tcp_t           *tcp = connp->conn_tcp;
5506 
5507         /* Assume IP provides aligned packets */
5508         ASSERT(OK_32PTR(mp->b_rptr));
5509         ASSERT((MBLKL(mp) >= sizeof (ipha_t)));
5510 
5511         /*
5512          * It's possible we have a closed, but not yet destroyed, TCP
5513          * connection. Several fields (e.g. conn_ixa->ixa_ire) are invalid
5514          * in the closed state, so don't take any chances and drop the packet.
5515          */
5516         if (tcp->tcp_state == TCPS_CLOSED) {
5517                 freemsg(mp);
5518                 return;
5519         }
5520 
5521         /*
5522          * Verify IP version. Anything other than IPv4 or IPv6 packet is sent
5523          * upstream. ICMPv6 is handled in tcp_icmp_error_ipv6.
5524          */
5525         if (!(ira->ira_flags & IRAF_IS_IPV4)) {
5526                 tcp_icmp_error_ipv6(tcp, mp, ira);
5527                 return;
5528         }
5529 
5530         /* Skip past the outer IP and ICMP headers */
5531         iph_hdr_length = ira->ira_ip_hdr_length;
5532         icmph = (icmph_t *)&mp->b_rptr[iph_hdr_length];
5533         /*
5534          * If we don't have the correct outer IP header length
5535          * or if we don't have a complete inner IP header
5536          * drop it.
5537          */
5538         if (iph_hdr_length < sizeof (ipha_t) ||
5539             (ipha_t *)&icmph[1] + 1 > (ipha_t *)mp->b_wptr) {
5540 noticmpv4:
5541                 freemsg(mp);
5542                 return;
5543         }
5544         ipha = (ipha_t *)&icmph[1];
5545 
5546         /* Skip past the inner IP and find the ULP header */
5547         iph_hdr_length = IPH_HDR_LENGTH(ipha);
5548         tcpha = (tcpha_t *)((char *)ipha + iph_hdr_length);
5549         /*
5550          * If we don't have the correct inner IP header length or if the ULP
5551          * is not IPPROTO_TCP or if we don't have at least ICMP_MIN_TCP_HDR
5552          * bytes of TCP header, drop it.
5553          */
5554         if (iph_hdr_length < sizeof (ipha_t) ||
5555             ipha->ipha_protocol != IPPROTO_TCP ||
5556             (uchar_t *)tcpha + ICMP_MIN_TCP_HDR > mp->b_wptr) {
5557                 goto noticmpv4;
5558         }
5559 
5560         seg_seq = ntohl(tcpha->tha_seq);
5561         switch (icmph->icmph_type) {
5562         case ICMP_DEST_UNREACHABLE:
5563                 switch (icmph->icmph_code) {
5564                 case ICMP_FRAGMENTATION_NEEDED:
5565                         /*
5566                          * Update Path MTU, then try to send something out.
5567                          */
5568                         tcp_update_pmtu(tcp, B_TRUE);
5569                         tcp_rexmit_after_error(tcp);
5570                         break;
5571                 case ICMP_PORT_UNREACHABLE:
5572                 case ICMP_PROTOCOL_UNREACHABLE:
5573                         switch (tcp->tcp_state) {
5574                         case TCPS_SYN_SENT:
5575                         case TCPS_SYN_RCVD:
5576                                 /*
5577                                  * ICMP can snipe away incipient
5578                                  * TCP connections as long as
5579                                  * seq number is same as initial
5580                                  * send seq number.
5581                                  */
5582                                 if (seg_seq == tcp->tcp_iss) {
5583                                         (void) tcp_clean_death(tcp,
5584                                             ECONNREFUSED);
5585                                 }
5586                                 break;
5587                         }
5588                         break;
5589                 case ICMP_HOST_UNREACHABLE:
5590                 case ICMP_NET_UNREACHABLE:
5591                         /* Record the error in case we finally time out. */
5592                         if (icmph->icmph_code == ICMP_HOST_UNREACHABLE)
5593                                 tcp->tcp_client_errno = EHOSTUNREACH;
5594                         else
5595                                 tcp->tcp_client_errno = ENETUNREACH;
5596                         if (tcp->tcp_state == TCPS_SYN_RCVD) {
5597                                 if (tcp->tcp_listener != NULL &&
5598                                     tcp->tcp_listener->tcp_syn_defense) {
5599                                         /*
5600                                          * Ditch the half-open connection if we
5601                                          * suspect a SYN attack is under way.
5602                                          */
5603                                         (void) tcp_clean_death(tcp,
5604                                             tcp->tcp_client_errno);
5605                                 }
5606                         }
5607                         break;
5608                 default:
5609                         break;
5610                 }
5611                 break;
5612         case ICMP_SOURCE_QUENCH: {
5613                 /*
5614                  * use a global boolean to control
5615                  * whether TCP should respond to ICMP_SOURCE_QUENCH.
5616                  * The default is false.
5617                  */
5618                 if (tcp_icmp_source_quench) {
5619                         /*
5620                          * Reduce the sending rate as if we got a
5621                          * retransmit timeout
5622                          */
5623                         uint32_t npkt;
5624 
5625                         npkt = ((tcp->tcp_snxt - tcp->tcp_suna) >> 1) /
5626                             tcp->tcp_mss;
5627                         tcp->tcp_cwnd_ssthresh = MAX(npkt, 2) * tcp->tcp_mss;
5628                         tcp->tcp_cwnd = tcp->tcp_mss;
5629                         tcp->tcp_cwnd_cnt = 0;
5630                 }
5631                 break;
5632         }
5633         }
5634         freemsg(mp);
5635 }
5636 
5637 /*
5638  * tcp_icmp_error_ipv6 is called from tcp_icmp_input to process ICMPv6
5639  * error messages passed up by IP.
5640  * Assumes that IP has pulled up all the extension headers as well
5641  * as the ICMPv6 header.
5642  */
5643 static void
5644 tcp_icmp_error_ipv6(tcp_t *tcp, mblk_t *mp, ip_recv_attr_t *ira)
5645 {
5646         icmp6_t         *icmp6;
5647         ip6_t           *ip6h;
5648         uint16_t        iph_hdr_length = ira->ira_ip_hdr_length;
5649         tcpha_t         *tcpha;
5650         uint8_t         *nexthdrp;
5651         uint32_t        seg_seq;
5652 
5653         /*
5654          * Verify that we have a complete IP header.
5655          */
5656         ASSERT((MBLKL(mp) >= sizeof (ip6_t)));
5657 
5658         icmp6 = (icmp6_t *)&mp->b_rptr[iph_hdr_length];
5659         ip6h = (ip6_t *)&icmp6[1];
5660         /*
5661          * Verify if we have a complete ICMP and inner IP header.
5662          */
5663         if ((uchar_t *)&ip6h[1] > mp->b_wptr) {
5664 noticmpv6:
5665                 freemsg(mp);
5666                 return;
5667         }
5668 
5669         if (!ip_hdr_length_nexthdr_v6(mp, ip6h, &iph_hdr_length, &nexthdrp))
5670                 goto noticmpv6;
5671         tcpha = (tcpha_t *)((char *)ip6h + iph_hdr_length);
5672         /*
5673          * Validate inner header. If the ULP is not IPPROTO_TCP or if we don't
5674          * have at least ICMP_MIN_TCP_HDR bytes of  TCP header drop the
5675          * packet.
5676          */
5677         if ((*nexthdrp != IPPROTO_TCP) ||
5678             ((uchar_t *)tcpha + ICMP_MIN_TCP_HDR) > mp->b_wptr) {
5679                 goto noticmpv6;
5680         }
5681 
5682         seg_seq = ntohl(tcpha->tha_seq);
5683         switch (icmp6->icmp6_type) {
5684         case ICMP6_PACKET_TOO_BIG:
5685                 /*
5686                  * Update Path MTU, then try to send something out.
5687                  */
5688                 tcp_update_pmtu(tcp, B_TRUE);
5689                 tcp_rexmit_after_error(tcp);
5690                 break;
5691         case ICMP6_DST_UNREACH:
5692                 switch (icmp6->icmp6_code) {
5693                 case ICMP6_DST_UNREACH_NOPORT:
5694                         if (((tcp->tcp_state == TCPS_SYN_SENT) ||
5695                             (tcp->tcp_state == TCPS_SYN_RCVD)) &&
5696                             (seg_seq == tcp->tcp_iss)) {
5697                                 (void) tcp_clean_death(tcp, ECONNREFUSED);
5698                         }
5699                         break;
5700                 case ICMP6_DST_UNREACH_ADMIN:
5701                 case ICMP6_DST_UNREACH_NOROUTE:
5702                 case ICMP6_DST_UNREACH_BEYONDSCOPE:
5703                 case ICMP6_DST_UNREACH_ADDR:
5704                         /* Record the error in case we finally time out. */
5705                         tcp->tcp_client_errno = EHOSTUNREACH;
5706                         if (((tcp->tcp_state == TCPS_SYN_SENT) ||
5707                             (tcp->tcp_state == TCPS_SYN_RCVD)) &&
5708                             (seg_seq == tcp->tcp_iss)) {
5709                                 if (tcp->tcp_listener != NULL &&
5710                                     tcp->tcp_listener->tcp_syn_defense) {
5711                                         /*
5712                                          * Ditch the half-open connection if we
5713                                          * suspect a SYN attack is under way.
5714                                          */
5715                                         (void) tcp_clean_death(tcp,
5716                                             tcp->tcp_client_errno);
5717                                 }
5718                         }
5719 
5720 
5721                         break;
5722                 default:
5723                         break;
5724                 }
5725                 break;
5726         case ICMP6_PARAM_PROB:
5727                 /* If this corresponds to an ICMP_PROTOCOL_UNREACHABLE */
5728                 if (icmp6->icmp6_code == ICMP6_PARAMPROB_NEXTHEADER &&
5729                     (uchar_t *)ip6h + icmp6->icmp6_pptr ==
5730                     (uchar_t *)nexthdrp) {
5731                         if (tcp->tcp_state == TCPS_SYN_SENT ||
5732                             tcp->tcp_state == TCPS_SYN_RCVD) {
5733                                 (void) tcp_clean_death(tcp, ECONNREFUSED);
5734                         }
5735                         break;
5736                 }
5737                 break;
5738 
5739         case ICMP6_TIME_EXCEEDED:
5740         default:
5741                 break;
5742         }
5743         freemsg(mp);
5744 }
5745 
5746 /*
5747  * CALLED OUTSIDE OF SQUEUE! It can not follow any pointers that tcp might
5748  * change. But it can refer to fields like tcp_suna and tcp_snxt.
5749  *
5750  * Function tcp_verifyicmp is called as conn_verifyicmp to verify the ICMP
5751  * error messages received by IP. The message is always received on the correct
5752  * tcp_t.
5753  */
5754 /* ARGSUSED */
5755 boolean_t
5756 tcp_verifyicmp(conn_t *connp, void *arg2, icmph_t *icmph, icmp6_t *icmp6,
5757     ip_recv_attr_t *ira)
5758 {
5759         tcpha_t         *tcpha = (tcpha_t *)arg2;
5760         uint32_t        seq = ntohl(tcpha->tha_seq);
5761         tcp_t           *tcp = connp->conn_tcp;
5762 
5763         /*
5764          * TCP sequence number contained in payload of the ICMP error message
5765          * should be within the range SND.UNA <= SEG.SEQ < SND.NXT. Otherwise,
5766          * the message is either a stale ICMP error, or an attack from the
5767          * network. Fail the verification.
5768          */
5769         if (SEQ_LT(seq, tcp->tcp_suna) || SEQ_GEQ(seq, tcp->tcp_snxt))
5770                 return (B_FALSE);
5771 
5772         /* For "too big" we also check the ignore flag */
5773         if (ira->ira_flags & IRAF_IS_IPV4) {
5774                 ASSERT(icmph != NULL);
5775                 if (icmph->icmph_type == ICMP_DEST_UNREACHABLE &&
5776                     icmph->icmph_code == ICMP_FRAGMENTATION_NEEDED &&
5777                     tcp->tcp_tcps->tcps_ignore_path_mtu)
5778                         return (B_FALSE);
5779         } else {
5780                 ASSERT(icmp6 != NULL);
5781                 if (icmp6->icmp6_type == ICMP6_PACKET_TOO_BIG &&
5782                     tcp->tcp_tcps->tcps_ignore_path_mtu)
5783                         return (B_FALSE);
5784         }
5785         return (B_TRUE);
5786 }