1 /*
   2  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  * 1. Redistributions of source code must retain the above copyright
   8  *    notice, this list of conditions and the following disclaimer.
   9  * 2. Redistributions in binary form must reproduce the above copyright
  10  *    notice, this list of conditions and the following disclaimer in the
  11  *    documentation and/or other materials provided with the distribution.
  12  *
  13  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  14  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  15  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  16  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  17  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  18  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  19  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  20  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  21  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  22  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  23  */
  24 /*
  25  * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
  26  * Use is subject to license terms.
  27  */
  28 
  29 #include "includes.h"
  30 RCSID("$OpenBSD: auth2-pubkey.c,v 1.2 2002/05/31 11:35:15 markus Exp $");
  31 
  32 #include "ssh2.h"
  33 #include "xmalloc.h"
  34 #include "packet.h"
  35 #include "buffer.h"
  36 #include "log.h"
  37 #include "servconf.h"
  38 #include "compat.h"
  39 #include "bufaux.h"
  40 #include "auth.h"
  41 #include "key.h"
  42 #include "pathnames.h"
  43 #include "uidswap.h"
  44 #include "auth-options.h"
  45 #include "canohost.h"
  46 
  47 #ifdef USE_PAM
  48 #include <security/pam_appl.h>
  49 #include "auth-pam.h"
  50 #endif /* USE_PAM */
  51 
  52 /* import */
  53 extern ServerOptions options;
  54 extern u_char *session_id2;
  55 extern int session_id2_len;
  56 
  57 static void
  58 userauth_pubkey(Authctxt *authctxt)
  59 {
  60         Buffer b;
  61         Key *key = NULL;
  62         char *pkalg;
  63         u_char *pkblob, *sig;
  64         u_int alen, blen, slen;
  65         int have_sig, pktype;
  66         int authenticated = 0;
  67 
  68         if (!authctxt || !authctxt->method)
  69                 fatal("%s: missing context", __func__);
  70 
  71         have_sig = packet_get_char();
  72         if (datafellows & SSH_BUG_PKAUTH) {
  73                 debug2("userauth_pubkey: SSH_BUG_PKAUTH");
  74                 /* no explicit pkalg given */
  75                 pkblob = packet_get_string(&blen);
  76                 buffer_init(&b);
  77                 buffer_append(&b, pkblob, blen);
  78                 /* so we have to extract the pkalg from the pkblob */
  79                 pkalg = buffer_get_string(&b, &alen);
  80                 buffer_free(&b);
  81         } else {
  82                 pkalg = packet_get_string(&alen);
  83                 pkblob = packet_get_string(&blen);
  84         }
  85         pktype = key_type_from_name(pkalg);
  86         if (pktype == KEY_UNSPEC) {
  87                 /* this is perfectly legal */
  88                 log("userauth_pubkey: unsupported public key algorithm: %s",
  89                     pkalg);
  90                 goto done;
  91         }
  92         key = key_from_blob(pkblob, blen);
  93         if (key == NULL) {
  94                 error("userauth_pubkey: cannot decode key: %s", pkalg);
  95                 goto done;
  96         }
  97         if (key->type != pktype) {
  98                 error("userauth_pubkey: type mismatch for decoded key "
  99                     "(received %d, expected %d)", key->type, pktype);
 100                 goto done;
 101         }
 102 
 103         /* Detect and count abandonment */
 104         if (authctxt->method->method_data) {
 105                 Key     *prev_key;
 106                 unsigned char   *prev_pkblob;
 107                 int      prev_blen;
 108 
 109                 /*
 110                  * Check for earlier test of a key that was allowed but
 111                  * not followed up with a pubkey req for the same pubkey
 112                  * and with a signature.
 113                  */
 114                 prev_key = authctxt->method->method_data;
 115                 if ((prev_blen = key_to_blob(prev_key,
 116                             &prev_pkblob, NULL))) {
 117                         if (prev_blen != blen ||
 118                             memcmp(prev_pkblob, pkblob, blen) != 0) {
 119                                 authctxt->method->abandons++;
 120                                 authctxt->method->attempts++;
 121                         }
 122                 }
 123                 key_free(prev_key);
 124                 authctxt->method->method_data = NULL;
 125         }
 126 
 127         if (have_sig) {
 128                 sig = packet_get_string(&slen);
 129                 packet_check_eom();
 130                 buffer_init(&b);
 131                 if (datafellows & SSH_OLD_SESSIONID) {
 132                         buffer_append(&b, session_id2, session_id2_len);
 133                 } else {
 134                         buffer_put_string(&b, session_id2, session_id2_len);
 135                 }
 136                 /* reconstruct packet */
 137                 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
 138                 buffer_put_cstring(&b, authctxt->user);
 139                 buffer_put_cstring(&b,
 140                     datafellows & SSH_BUG_PKSERVICE ?
 141                     "ssh-userauth" :
 142                     authctxt->service);
 143                 if (datafellows & SSH_BUG_PKAUTH) {
 144                         buffer_put_char(&b, have_sig);
 145                 } else {
 146                         buffer_put_cstring(&b, "publickey");
 147                         buffer_put_char(&b, have_sig);
 148                         buffer_put_cstring(&b, pkalg);
 149                 }
 150                 buffer_put_string(&b, pkblob, blen);
 151 #ifdef DEBUG_PK
 152                 buffer_dump(&b);
 153 #endif
 154                 /* test for correct signature */
 155                 if (user_key_allowed(authctxt->pw, key) &&
 156                     key_verify(key, sig, slen, buffer_ptr(&b),
 157                     buffer_len(&b)) == 1) {
 158                         authenticated = 1;
 159                 }
 160                 authctxt->method->postponed = 0;
 161                 buffer_free(&b);
 162                 xfree(sig);
 163         } else {
 164                 debug("test whether pkalg/pkblob are acceptable");
 165                 packet_check_eom();
 166 
 167                 /* XXX fake reply and always send PK_OK ? */
 168                 /*
 169                  * XXX this allows testing whether a user is allowed
 170                  * to login: if you happen to have a valid pubkey this
 171                  * message is sent. the message is NEVER sent at all
 172                  * if a user is not allowed to login. is this an
 173                  * issue? -markus
 174                  */
 175                 if (user_key_allowed(authctxt->pw, key)) {
 176                         packet_start(SSH2_MSG_USERAUTH_PK_OK);
 177                         packet_put_string(pkalg, alen);
 178                         packet_put_string(pkblob, blen);
 179                         packet_send();
 180                         packet_write_wait();
 181                         authctxt->method->postponed = 1;
 182                         /*
 183                          * Remember key that was tried so we can
 184                          * correctly detect abandonment.  See above.
 185                          */
 186                         authctxt->method->method_data = (void *) key;
 187                         key = NULL;
 188                 }
 189         }
 190         if (authenticated != 1)
 191                 auth_clear_options();
 192 
 193 done:
 194         /*
 195          * XXX TODO: add config options for specifying users for whom
 196          * this userauth is insufficient and what userauths may
 197          * continue.
 198          */
 199 #ifdef USE_PAM
 200         if (authenticated) {
 201                 if (!do_pam_non_initial_userauth(authctxt))
 202                         authenticated = 0;
 203         }
 204 #endif /* USE_PAM */
 205 
 206         debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg);
 207         if (key != NULL)
 208                 key_free(key);
 209         xfree(pkalg);
 210         xfree(pkblob);
 211 #ifdef HAVE_CYGWIN
 212         if (check_nt_auth(0, authctxt->pw) == 0)
 213                 return;
 214 #endif
 215         if (authenticated)
 216                 authctxt->method->authenticated = 1;
 217 }
 218 
 219 /* return 1 if user allows given key */
 220 static int
 221 user_key_allowed2(struct passwd *pw, Key *key, char *file)
 222 {
 223         char line[8192];
 224         int found_key = 0;
 225         FILE *f;
 226         u_long linenum = 0;
 227         struct stat st;
 228         Key *found;
 229         char *fp;
 230 
 231         if (pw == NULL)
 232                 return 0;
 233 
 234         /* Temporarily use the user's uid. */
 235         temporarily_use_uid(pw);
 236 
 237         debug("trying public key file %s", file);
 238 
 239         /* Fail quietly if file does not exist */
 240         if (stat(file, &st) < 0) {
 241                 /* Restore the privileged uid. */
 242                 restore_uid();
 243                 return 0;
 244         }
 245         /* Open the file containing the authorized keys. */
 246         f = fopen(file, "r");
 247         if (!f) {
 248                 /* Restore the privileged uid. */
 249                 restore_uid();
 250                 return 0;
 251         }
 252         if (options.strict_modes &&
 253             secure_filename(f, file, pw, line, sizeof(line)) != 0) {
 254                 (void) fclose(f);
 255                 log("Authentication refused: %s", line);
 256                 restore_uid();
 257                 return 0;
 258         }
 259 
 260         found_key = 0;
 261         found = key_new(key->type);
 262 
 263         while (fgets(line, sizeof(line), f)) {
 264                 char *cp, *options = NULL;
 265                 linenum++;
 266                 /* Skip leading whitespace, empty and comment lines. */
 267                 for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
 268                         ;
 269                 if (!*cp || *cp == '\n' || *cp == '#')
 270                         continue;
 271 
 272                 if (key_read(found, &cp) != 1) {
 273                         /* no key?  check if there are options for this key */
 274                         int quoted = 0;
 275                         debug2("user_key_allowed: check options: '%s'", cp);
 276                         options = cp;
 277                         for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
 278                                 if (*cp == '\\' && cp[1] == '"')
 279                                         cp++;   /* Skip both */
 280                                 else if (*cp == '"')
 281                                         quoted = !quoted;
 282                         }
 283                         /* Skip remaining whitespace. */
 284                         for (; *cp == ' ' || *cp == '\t'; cp++)
 285                                 ;
 286                         if (key_read(found, &cp) != 1) {
 287                                 debug2("user_key_allowed: advance: '%s'", cp);
 288                                 /* still no key?  advance to next line*/
 289                                 continue;
 290                         }
 291                 }
 292                 if (key_equal(found, key) &&
 293                     auth_parse_options(pw, options, file, linenum) == 1) {
 294                         found_key = 1;
 295                         debug("matching key found: file %s, line %lu",
 296                             file, linenum);
 297                         fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
 298                         verbose("Found matching %s key: %s",
 299                             key_type(found), fp);
 300                         xfree(fp);
 301                         break;
 302                 }
 303         }
 304         restore_uid();
 305         (void) fclose(f);
 306         key_free(found);
 307         if (!found_key)
 308                 debug2("key not found");
 309         return found_key;
 310 }
 311 
 312 /* check whether given key is in .ssh/authorized_keys* */
 313 int
 314 user_key_allowed(struct passwd *pw, Key *key)
 315 {
 316         int success;
 317         char *file;
 318 
 319         if (pw == NULL)
 320                 return 0;
 321 
 322         file = authorized_keys_file(pw);
 323         success = user_key_allowed2(pw, key, file);
 324         xfree(file);
 325         if (success)
 326                 return success;
 327 
 328         /* try suffix "2" for backward compat, too */
 329         file = authorized_keys_file2(pw);
 330         success = user_key_allowed2(pw, key, file);
 331         xfree(file);
 332         return success;
 333 }
 334 
 335 static
 336 void
 337 userauth_pubkey_abandon(Authctxt *authctxt, Authmethod *method)
 338 {
 339         if (!authctxt || !method)
 340                 return;
 341 
 342         if (method->method_data) {
 343                 method->abandons++;
 344                 method->attempts++;
 345                 key_free((Key *) method->method_data);
 346                 method->method_data = NULL;
 347         }
 348 }
 349 
 350 Authmethod method_pubkey = {
 351         "publickey",
 352         &options.pubkey_authentication,
 353         userauth_pubkey,
 354         userauth_pubkey_abandon,
 355         NULL, NULL,         /* method data and hist data */
 356         0,                  /* not initial userauth */
 357         0, 0, 0,            /* counters */
 358         0, 0, 0, 0, 0, 0    /* state */
 359 };