1 /*
   2  * Author: Tatu Ylonen <ylo@cs.hut.fi>
   3  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
   4  *                    All rights reserved
   5  * Rhosts authentication.  This file contains code to check whether to admit
   6  * the login based on rhosts authentication.  This file also processes
   7  * /etc/hosts.equiv.
   8  *
   9  * As far as I am concerned, the code I have written for this software
  10  * can be used freely for any purpose.  Any derived versions of this
  11  * software must be clearly marked as such, and if the derived work is
  12  * incompatible with the protocol description in the RFC file, it must be
  13  * called by a name other than "ssh" or "Secure Shell".
  14  */
  15 
  16 #include "includes.h"
  17 RCSID("$OpenBSD: auth-rhosts.c,v 1.28 2002/05/13 21:26:49 markus Exp $");
  18 
  19 #pragma ident   "%Z%%M% %I%     %E% SMI"
  20 
  21 #include "packet.h"
  22 #include "uidswap.h"
  23 #include "pathnames.h"
  24 #include "log.h"
  25 #include "servconf.h"
  26 #include "canohost.h"
  27 #include "auth.h"
  28 
  29 /* import */
  30 extern ServerOptions options;
  31 
  32 /*
  33  * This function processes an rhosts-style file (.rhosts, .shosts, or
  34  * /etc/hosts.equiv).  This returns true if authentication can be granted
  35  * based on the file, and returns zero otherwise.
  36  */
  37 
  38 static int
  39 check_rhosts_file(const char *filename, const char *hostname,
  40                   const char *ipaddr, const char *client_user,
  41                   const char *server_user)
  42 {
  43         FILE *f;
  44         char buf[1024]; /* Must not be larger than host, user, dummy below. */
  45 
  46         /* Open the .rhosts file, deny if unreadable */
  47         f = fopen(filename, "r");
  48         if (!f)
  49                 return 0;
  50 
  51         while (fgets(buf, sizeof(buf), f)) {
  52                 /* All three must be at least as big as buf to avoid overflows. */
  53                 char hostbuf[1024], userbuf[1024], dummy[1024], *host, *user, *cp;
  54                 int negated;
  55 
  56                 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
  57                         ;
  58                 if (*cp == '#' || *cp == '\n' || !*cp)
  59                         continue;
  60 
  61                 /*
  62                  * NO_PLUS is supported at least on OSF/1.  We skip it (we
  63                  * don't ever support the plus syntax).
  64                  */
  65                 if (strncmp(cp, "NO_PLUS", 7) == 0)
  66                         continue;
  67 
  68                 /*
  69                  * This should be safe because each buffer is as big as the
  70                  * whole string, and thus cannot be overwritten.
  71                  */
  72                 switch (sscanf(buf, "%1024s %1024s %1024s",
  73                                 hostbuf, userbuf, dummy)) {
  74                 case 0:
  75                         auth_debug_add("Found empty line in %.100s.", filename);
  76                         continue;
  77                 case 1:
  78                         /* Host name only. */
  79                         strlcpy(userbuf, server_user, sizeof(userbuf));
  80                         break;
  81                 case 2:
  82                         /* Got both host and user name. */
  83                         break;
  84                 case 3:
  85                         auth_debug_add("Found garbage in %.100s.", filename);
  86                         continue;
  87                 default:
  88                         /* Weird... */
  89                         continue;
  90                 }
  91 
  92                 host = hostbuf;
  93                 user = userbuf;
  94                 negated = 0;
  95 
  96                 /* Process negated host names, or positive netgroups. */
  97                 if (host[0] == '-') {
  98                         negated = 1;
  99                         host++;
 100                 } else if (host[0] == '+')
 101                         host++;
 102 
 103                 if (user[0] == '-') {
 104                         negated = 1;
 105                         user++;
 106                 } else if (user[0] == '+')
 107                         user++;
 108 
 109                 /* Check for empty host/user names (particularly '+'). */
 110                 if (!host[0] || !user[0]) {
 111                         /* We come here if either was '+' or '-'. */
 112                         auth_debug_add("Ignoring wild host/user names in %.100s.",
 113                             filename);
 114                         continue;
 115                 }
 116                 /* Verify that host name matches. */
 117                 if (host[0] == '@') {
 118                         if (!innetgr(host + 1, hostname, NULL, NULL) &&
 119                             !innetgr(host + 1, ipaddr, NULL, NULL))
 120                                 continue;
 121                 } else if (strcasecmp(host, hostname) && strcmp(host, ipaddr) != 0)
 122                         continue;       /* Different hostname. */
 123 
 124                 /* Verify that user name matches. */
 125                 if (user[0] == '@') {
 126                         if (!innetgr(user + 1, NULL, client_user, NULL))
 127                                 continue;
 128                 } else if (strcmp(user, client_user) != 0)
 129                         continue;       /* Different username. */
 130 
 131                 /* Found the user and host. */
 132                 fclose(f);
 133 
 134                 /* If the entry was negated, deny access. */
 135                 if (negated) {
 136                         auth_debug_add("Matched negative entry in %.100s.",
 137                              filename);
 138                         return 0;
 139                 }
 140                 /* Accept authentication. */
 141                 return 1;
 142         }
 143 
 144         /* Authentication using this file denied. */
 145         fclose(f);
 146         return 0;
 147 }
 148 
 149 /*
 150  * Tries to authenticate the user using the .shosts or .rhosts file. Returns
 151  * true if authentication succeeds.  If ignore_rhosts is true, only
 152  * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
 153  */
 154 
 155 int
 156 auth_rhosts(struct passwd *pw, const char *client_user)
 157 {
 158         const char *hostname, *ipaddr;
 159 
 160         hostname = get_canonical_hostname(options.verify_reverse_mapping);
 161         ipaddr = get_remote_ipaddr();
 162         return auth_rhosts2(pw, client_user, hostname, ipaddr);
 163 }
 164 
 165 static int
 166 auth_rhosts2_raw(struct passwd *pw, const char *client_user, const char *hostname,
 167     const char *ipaddr)
 168 {
 169         char buf[1024];
 170         struct stat st;
 171         static const char *rhosts_files[] = {".shosts", ".rhosts", NULL};
 172         u_int rhosts_file_index;
 173 
 174         debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s",
 175             client_user, hostname, ipaddr);
 176 
 177         /* no user given */
 178         if (pw == NULL)
 179                 return 0;
 180 
 181         /* Switch to the user's uid. */
 182         temporarily_use_uid(pw);
 183         /*
 184          * Quick check: if the user has no .shosts or .rhosts files, return
 185          * failure immediately without doing costly lookups from name
 186          * servers.
 187          */
 188         for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
 189             rhosts_file_index++) {
 190                 /* Check users .rhosts or .shosts. */
 191                 snprintf(buf, sizeof buf, "%.500s/%.100s",
 192                          pw->pw_dir, rhosts_files[rhosts_file_index]);
 193                 if (stat(buf, &st) >= 0)
 194                         break;
 195         }
 196         /* Switch back to privileged uid. */
 197         restore_uid();
 198 
 199         /* Deny if The user has no .shosts or .rhosts file and there are no system-wide files. */
 200         if (!rhosts_files[rhosts_file_index] &&
 201             stat(_PATH_RHOSTS_EQUIV, &st) < 0 &&
 202             stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0)
 203                 return 0;
 204 
 205         /* If not logging in as superuser, try /etc/hosts.equiv and shosts.equiv. */
 206         if (pw->pw_uid != 0) {
 207                 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr,
 208                     client_user, pw->pw_name)) {
 209                         auth_debug_add("Accepted for %.100s [%.100s] by /etc/hosts.equiv.",
 210                             hostname, ipaddr);
 211                         return 1;
 212                 }
 213                 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr,
 214                     client_user, pw->pw_name)) {
 215                         auth_debug_add("Accepted for %.100s [%.100s] by %.100s.",
 216                             hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV);
 217                         return 1;
 218                 }
 219         }
 220         /*
 221          * Check that the home directory is owned by root or the user, and is
 222          * not group or world writable.
 223          */
 224         if (stat(pw->pw_dir, &st) < 0) {
 225                 log("Rhosts authentication refused for %.100s: "
 226                     "no home directory %.200s", pw->pw_name, pw->pw_dir);
 227                 auth_debug_add("Rhosts authentication refused for %.100s: "
 228                     "no home directory %.200s", pw->pw_name, pw->pw_dir);
 229                 return 0;
 230         }
 231         if (options.strict_modes &&
 232             ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
 233             (st.st_mode & 022) != 0)) {
 234                 log("Rhosts authentication refused for %.100s: "
 235                     "bad ownership or modes for home directory.", pw->pw_name);
 236                 auth_debug_add("Rhosts authentication refused for %.100s: "
 237                     "bad ownership or modes for home directory.", pw->pw_name);
 238                 return 0;
 239         }
 240         /* Temporarily use the user's uid. */
 241         temporarily_use_uid(pw);
 242 
 243         /* Check all .rhosts files (currently .shosts and .rhosts). */
 244         for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
 245             rhosts_file_index++) {
 246                 /* Check users .rhosts or .shosts. */
 247                 snprintf(buf, sizeof buf, "%.500s/%.100s",
 248                          pw->pw_dir, rhosts_files[rhosts_file_index]);
 249                 if (stat(buf, &st) < 0)
 250                         continue;
 251 
 252                 /*
 253                  * Make sure that the file is either owned by the user or by
 254                  * root, and make sure it is not writable by anyone but the
 255                  * owner.  This is to help avoid novices accidentally
 256                  * allowing access to their account by anyone.
 257                  */
 258                 if (options.strict_modes &&
 259                     ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
 260                     (st.st_mode & 022) != 0)) {
 261                         log("Rhosts authentication refused for %.100s: bad modes for %.200s",
 262                             pw->pw_name, buf);
 263                         auth_debug_add("Bad file modes for %.200s", buf);
 264                         continue;
 265                 }
 266                 /* Check if we have been configured to ignore .rhosts and .shosts files. */
 267                 if (options.ignore_rhosts) {
 268                         auth_debug_add("Server has been configured to ignore %.100s.",
 269                             rhosts_files[rhosts_file_index]);
 270                         continue;
 271                 }
 272                 /* Check if authentication is permitted by the file. */
 273                 if (check_rhosts_file(buf, hostname, ipaddr, client_user, pw->pw_name)) {
 274                         auth_debug_add("Accepted by %.100s.",
 275                             rhosts_files[rhosts_file_index]);
 276                         /* Restore the privileged uid. */
 277                         restore_uid();
 278                         auth_debug_add("Accepted host %s ip %s client_user %s server_user %s",
 279                                 hostname, ipaddr, client_user, pw->pw_name);
 280                         return 1;
 281                 }
 282         }
 283 
 284         /* Restore the privileged uid. */
 285         restore_uid();
 286         return 0;
 287 }
 288 
 289 int
 290 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
 291     const char *ipaddr)
 292 {
 293         int ret;
 294 
 295         auth_debug_reset();
 296         ret = auth_rhosts2_raw(pw, client_user, hostname, ipaddr);
 297         auth_debug_send();
 298         return ret;
 299 }