auth-rhosts.c

   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 1.32 2003/11/04 08:54:09 djm Exp $");
  18
  19 #include "packet.h"
  20 #include "uidswap.h"
  21 #include "pathnames.h"
  22 #include "log.h"
  23 #include "servconf.h"
  24 #include "canohost.h"
  25 #include "auth.h"
  26
  27 /* import */
  28 extern ServerOptions options;
  29 extern int use_privsep;
  30
  31 /*
  32  * This function processes an rhosts-style file (.rhosts, .shosts, or
  33  * /etc/hosts.equiv).  This returns true if authentication can be granted
  34  * based on the file, and returns zero otherwise.
  35  */
  36
  37 static int
  38 check_rhosts_file(const char *filename, const char *hostname,
  39                   const char *ipaddr, const char *client_user,
  40                   const char *server_user)
  41 {
  42         FILE *f;
  43         char buf[1024]; /* Must not be larger than host, user, dummy below. */
  44
  45         /* Open the .rhosts file, deny if unreadable */
  46         f = fopen(filename, "r");
  47         if (!f)
  48                 return 0;
  49
  50         while (fgets(buf, sizeof(buf), f)) {
  51                 /* All three must be at least as big as buf to avoid overflows. */
  52                 char hostbuf[1024], userbuf[1024], dummy[1024], *host, *user, *cp;
  53                 int negated;
  54
  55                 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
  56                         ;
  57                 if (*cp == '#' || *cp == '\n' || !*cp)
  58                         continue;
  59
  60                 /*
  61                  * NO_PLUS is supported at least on OSF/1.  We skip it (we
  62                  * don't ever support the plus syntax).
  63                  */
  64                 if (strncmp(cp, "NO_PLUS", 7) == 0)
  65                         continue;
  66
  67                 /*
  68                  * This should be safe because each buffer is as big as the
  69                  * whole string, and thus cannot be overwritten.
  70                  */
  71                 switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf,
  72                     dummy)) {
  73                 case 0:
  74                         auth_debug_add("Found empty line in %.100s.", filename);
  75                         continue;
  76                 case 1:
  77                         /* Host name only. */
  78                         strlcpy(userbuf, server_user, sizeof(userbuf));
  79                         break;
  80                 case 2:
  81                         /* Got both host and user name. */
  82                         break;
  83                 case 3:
  84                         auth_debug_add("Found garbage in %.100s.", filename);
  85                         continue;
  86                 default:
  87                         /* Weird... */
  88                         continue;
  89                 }
  90
  91                 host = hostbuf;
  92                 user = userbuf;
  93                 negated = 0;
  94
  95                 /* Process negated host names, or positive netgroups. */
  96                 if (host[0] == '-') {
  97                         negated = 1;
  98                         host++;
  99                 } else if (host[0] == '+')
 100                         host++;
 101
 102                 if (user[0] == '-') {
 103                         negated = 1;
 104                         user++;
 105                 } else if (user[0] == '+')
 106                         user++;
 107
 108                 /* Check for empty host/user names (particularly '+'). */
 109                 if (!host[0] || !user[0]) {
 110                         /* We come here if either was '+' or '-'. */
 111                         auth_debug_add("Ignoring wild host/user names in %.100s.",
 112                             filename);
 113                         continue;
 114                 }
 115                 /* Verify that host name matches. */
 116                 if (host[0] == '@') {
 117                         if (!innetgr(host + 1, hostname, NULL, NULL) &&
 118                             !innetgr(host + 1, ipaddr, NULL, NULL))
 119                                 continue;
 120                 } else if (strcasecmp(host, hostname) && strcmp(host, ipaddr) != 0)
 121                         continue;       /* Different hostname. */
 122
 123                 /* Verify that user name matches. */
 124                 if (user[0] == '@') {
 125                         if (!innetgr(user + 1, NULL, client_user, NULL))
 126                                 continue;
 127                 } else if (strcmp(user, client_user) != 0)
 128                         continue;       /* Different username. */
 129
 130                 /* Found the user and host. */
 131                 fclose(f);
 132
 133                 /* If the entry was negated, deny access. */
 134                 if (negated) {
 135                         auth_debug_add("Matched negative entry in %.100s.",
 136                              filename);
 137                         return 0;
 138                 }
 139                 /* Accept authentication. */
 140                 return 1;
 141         }
 142
 143         /* Authentication using this file denied. */
 144         fclose(f);
 145         return 0;
 146 }
 147
 148 /*
 149  * Tries to authenticate the user using the .shosts or .rhosts file. Returns
 150  * true if authentication succeeds.  If ignore_rhosts is true, only
 151  * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
 152  */
 153
 154 int
 155 auth_rhosts(struct passwd *pw, const char *client_user)
 156 {
 157         const char *hostname, *ipaddr;
 158
 159         hostname = get_canonical_hostname(options.use_dns);
 160         ipaddr = get_remote_ipaddr();
 161         return auth_rhosts2(pw, client_user, hostname, ipaddr);
 162 }
 163
 164 static int
 165 auth_rhosts2_raw(struct passwd *pw, const char *client_user, const char *hostname,
 166     const char *ipaddr)
 167 {
 168         char buf[1024];
 169         struct stat st;
 170         static const char *rhosts_files[] = {".shosts", ".rhosts", NULL};
 171         u_int rhosts_file_index;
 172
 173         debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s",
 174             client_user, hostname, ipaddr);
 175
 176         /* Switch to the user's uid. */
 177         temporarily_use_uid(pw);
 178         /*
 179          * Quick check: if the user has no .shosts or .rhosts files, return
 180          * failure immediately without doing costly lookups from name
 181          * servers.
 182          */
 183         for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
 184             rhosts_file_index++) {
 185                 /* Check users .rhosts or .shosts. */
 186                 snprintf(buf, sizeof buf, "%.500s/%.100s",
 187                          pw->pw_dir, rhosts_files[rhosts_file_index]);
 188                 if (stat(buf, &st) >= 0)
 189                         break;
 190         }
 191         /* Switch back to privileged uid. */
 192         restore_uid();
 193
 194         /* Deny if The user has no .shosts or .rhosts file and there are no system-wide files. */
 195         if (!rhosts_files[rhosts_file_index] &&
 196             stat(_PATH_RHOSTS_EQUIV, &st) < 0 &&
 197             stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0)
 198                 return 0;
 199
 200         /* If not logging in as superuser, try /etc/hosts.equiv and shosts.equiv. */
 201         if (pw->pw_uid != 0) {
 202                 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr,
 203                     client_user, pw->pw_name)) {
 204                         auth_debug_add("Accepted for %.100s [%.100s] by /etc/hosts.equiv.",
 205                             hostname, ipaddr);
 206                         return 1;
 207                 }
 208                 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr,
 209                     client_user, pw->pw_name)) {
 210                         auth_debug_add("Accepted for %.100s [%.100s] by %.100s.",
 211                             hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV);
 212                         return 1;
 213                 }
 214         }
 215         /*
 216          * Check that the home directory is owned by root or the user, and is
 217          * not group or world writable.
 218          */
 219         if (stat(pw->pw_dir, &st) < 0) {
 220                 logit("Rhosts authentication refused for %.100s: "
 221                     "no home directory %.200s", pw->pw_name, pw->pw_dir);
 222                 auth_debug_add("Rhosts authentication refused for %.100s: "
 223                     "no home directory %.200s", pw->pw_name, pw->pw_dir);
 224                 return 0;
 225         }
 226         if (options.strict_modes &&
 227             ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
 228             (st.st_mode & 022) != 0)) {
 229                 logit("Rhosts authentication refused for %.100s: "
 230                     "bad ownership or modes for home directory.", pw->pw_name);
 231                 auth_debug_add("Rhosts authentication refused for %.100s: "
 232                     "bad ownership or modes for home directory.", pw->pw_name);
 233                 return 0;
 234         }
 235         /* Temporarily use the user's uid. */
 236         temporarily_use_uid(pw);
 237
 238         /* Check all .rhosts files (currently .shosts and .rhosts). */
 239         for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
 240             rhosts_file_index++) {
 241                 /* Check users .rhosts or .shosts. */
 242                 snprintf(buf, sizeof buf, "%.500s/%.100s",
 243                          pw->pw_dir, rhosts_files[rhosts_file_index]);
 244                 if (stat(buf, &st) < 0)
 245                         continue;
 246
 247                 /*
 248                  * Make sure that the file is either owned by the user or by
 249                  * root, and make sure it is not writable by anyone but the
 250                  * owner.  This is to help avoid novices accidentally
 251                  * allowing access to their account by anyone.
 252                  */
 253                 if (options.strict_modes &&
 254                     ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
 255                     (st.st_mode & 022) != 0)) {
 256                         logit("Rhosts authentication refused for %.100s: bad modes for %.200s",
 257                             pw->pw_name, buf);
 258                         auth_debug_add("Bad file modes for %.200s", buf);
 259                         continue;
 260                 }
 261                 /* Check if we have been configured to ignore .rhosts and .shosts files. */
 262                 if (options.ignore_rhosts) {
 263                         auth_debug_add("Server has been configured to ignore %.100s.",
 264                             rhosts_files[rhosts_file_index]);
 265                         continue;
 266                 }
 267                 /* Check if authentication is permitted by the file. */
 268                 if (check_rhosts_file(buf, hostname, ipaddr, client_user, pw->pw_name)) {
 269                         auth_debug_add("Accepted by %.100s.",
 270                             rhosts_files[rhosts_file_index]);
 271                         /* Restore the privileged uid. */
 272                         restore_uid();
 273                         auth_debug_add("Accepted host %s ip %s client_user %s server_user %s",
 274                                 hostname, ipaddr, client_user, pw->pw_name);
 275                         return 1;
 276                 }
 277         }
 278
 279         /* Restore the privileged uid. */
 280         restore_uid();
 281         return 0;
 282 }
 283
 284 int
 285 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
 286     const char *ipaddr)
 287 {
 288         int ret;
 289
 290         auth_debug_reset();
 291         ret = auth_rhosts2_raw(pw, client_user, hostname, ipaddr);
 292         if (!use_privsep)
 293                 auth_debug_send();
 294         return ret;
 295 }