auth-rhosts.c

   1 /* $OpenBSD: auth-rhosts.c,v 1.43 2008/06/13 14:18:51 dtucker Exp $ */
   2 /*
   3  * Author: Tatu Ylonen <ylo@cs.hut.fi>
   4  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
   5  *                    All rights reserved
   6  * Rhosts authentication.  This file contains code to check whether to admit
   7  * the login based on rhosts authentication.  This file also processes
   8  * /etc/hosts.equiv.
   9  *
  10  * As far as I am concerned, the code I have written for this software
  11  * can be used freely for any purpose.  Any derived versions of this
  12  * software must be clearly marked as such, and if the derived work is
  13  * incompatible with the protocol description in the RFC file, it must be
  14  * called by a name other than "ssh" or "Secure Shell".
  15  */
  16
  17 #include "includes.h"
  18
  19 #include <sys/types.h>
  20 #include <sys/stat.h>
  21
  22 #ifdef HAVE_NETGROUP_H
  23 # include <netgroup.h>
  24 #endif
  25 #include <pwd.h>
  26 #include <stdio.h>
  27 #include <string.h>
  28 #include <stdarg.h>
  29 #include <fcntl.h>
  30 #include <unistd.h>
  31
  32 #include "packet.h"
  33 #include "buffer.h"
  34 #include "uidswap.h"
  35 #include "pathnames.h"
  36 #include "log.h"
  37 #include "servconf.h"
  38 #include "canohost.h"
  39 #include "key.h"
  40 #include "hostfile.h"
  41 #include "auth.h"
  42 #include "misc.h"
  43
  44 /* import */
  45 extern ServerOptions options;
  46 extern int use_privsep;
  47
  48 /*
  49  * This function processes an rhosts-style file (.rhosts, .shosts, or
  50  * /etc/hosts.equiv).  This returns true if authentication can be granted
  51  * based on the file, and returns zero otherwise.
  52  */
  53
  54 static int
  55 check_rhosts_file(const char *filename, const char *hostname,
  56                   const char *ipaddr, const char *client_user,
  57                   const char *server_user)
  58 {
  59         FILE *f;
  60         char buf[1024]; /* Must not be larger than host, user, dummy below. */
  61         int fd;
  62         struct stat st;
  63
  64         /* Open the .rhosts file, deny if unreadable */
  65         if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1)
  66                 return 0;
  67         if (fstat(fd, &st) == -1) {
  68                 close(fd);
  69                 return 0;
  70         }
  71         if (!S_ISREG(st.st_mode)) {
  72                 logit("User %s hosts file %s is not a regular file",
  73                     server_user, filename);
  74                 close(fd);
  75                 return 0;
  76         }
  77         unset_nonblock(fd);
  78         if ((f = fdopen(fd, "r")) == NULL) {
  79                 close(fd);
  80                 return 0;
  81         }
  82         while (fgets(buf, sizeof(buf), f)) {
  83                 /* All three must be at least as big as buf to avoid overflows. */
  84                 char hostbuf[1024], userbuf[1024], dummy[1024], *host, *user, *cp;
  85                 int negated;
  86
  87                 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
  88                         ;
  89                 if (*cp == '#' || *cp == '\n' || !*cp)
  90                         continue;
  91
  92                 /*
  93                  * NO_PLUS is supported at least on OSF/1.  We skip it (we
  94                  * don't ever support the plus syntax).
  95                  */
  96                 if (strncmp(cp, "NO_PLUS", 7) == 0)
  97                         continue;
  98
  99                 /*
 100                  * This should be safe because each buffer is as big as the
 101                  * whole string, and thus cannot be overwritten.
 102                  */
 103                 switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf,
 104                     dummy)) {
 105                 case 0:
 106                         auth_debug_add("Found empty line in %.100s.", filename);
 107                         continue;
 108                 case 1:
 109                         /* Host name only. */
 110                         strlcpy(userbuf, server_user, sizeof(userbuf));
 111                         break;
 112                 case 2:
 113                         /* Got both host and user name. */
 114                         break;
 115                 case 3:
 116                         auth_debug_add("Found garbage in %.100s.", filename);
 117                         continue;
 118                 default:
 119                         /* Weird... */
 120                         continue;
 121                 }
 122
 123                 host = hostbuf;
 124                 user = userbuf;
 125                 negated = 0;
 126
 127                 /* Process negated host names, or positive netgroups. */
 128                 if (host[0] == '-') {
 129                         negated = 1;
 130                         host++;
 131                 } else if (host[0] == '+')
 132                         host++;
 133
 134                 if (user[0] == '-') {
 135                         negated = 1;
 136                         user++;
 137                 } else if (user[0] == '+')
 138                         user++;
 139
 140                 /* Check for empty host/user names (particularly '+'). */
 141                 if (!host[0] || !user[0]) {
 142                         /* We come here if either was '+' or '-'. */
 143                         auth_debug_add("Ignoring wild host/user names in %.100s.",
 144                             filename);
 145                         continue;
 146                 }
 147                 /* Verify that host name matches. */
 148                 if (host[0] == '@') {
 149                         if (!innetgr(host + 1, hostname, NULL, NULL) &&
 150                             !innetgr(host + 1, ipaddr, NULL, NULL))
 151                                 continue;
 152                 } else if (strcasecmp(host, hostname) && strcmp(host, ipaddr) != 0)
 153                         continue;       /* Different hostname. */
 154
 155                 /* Verify that user name matches. */
 156                 if (user[0] == '@') {
 157                         if (!innetgr(user + 1, NULL, client_user, NULL))
 158                                 continue;
 159                 } else if (strcmp(user, client_user) != 0)
 160                         continue;       /* Different username. */
 161
 162                 /* Found the user and host. */
 163                 fclose(f);
 164
 165                 /* If the entry was negated, deny access. */
 166                 if (negated) {
 167                         auth_debug_add("Matched negative entry in %.100s.",
 168                             filename);
 169                         return 0;
 170                 }
 171                 /* Accept authentication. */
 172                 return 1;
 173         }
 174
 175         /* Authentication using this file denied. */
 176         fclose(f);
 177         return 0;
 178 }
 179
 180 /*
 181  * Tries to authenticate the user using the .shosts or .rhosts file. Returns
 182  * true if authentication succeeds.  If ignore_rhosts is true, only
 183  * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
 184  */
 185
 186 int
 187 auth_rhosts(struct passwd *pw, const char *client_user)
 188 {
 189         const char *hostname, *ipaddr;
 190
 191         hostname = get_canonical_hostname(options.use_dns);
 192         ipaddr = get_remote_ipaddr();
 193         return auth_rhosts2(pw, client_user, hostname, ipaddr);
 194 }
 195
 196 static int
 197 auth_rhosts2_raw(struct passwd *pw, const char *client_user, const char *hostname,
 198     const char *ipaddr)
 199 {
 200         char buf[1024];
 201         struct stat st;
 202         static const char *rhosts_files[] = {".shosts", ".rhosts", NULL};
 203         u_int rhosts_file_index;
 204
 205         debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s",
 206             client_user, hostname, ipaddr);
 207
 208         /* Switch to the user's uid. */
 209         temporarily_use_uid(pw);
 210         /*
 211          * Quick check: if the user has no .shosts or .rhosts files, return
 212          * failure immediately without doing costly lookups from name
 213          * servers.
 214          */
 215         for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
 216             rhosts_file_index++) {
 217                 /* Check users .rhosts or .shosts. */
 218                 snprintf(buf, sizeof buf, "%.500s/%.100s",
 219                          pw->pw_dir, rhosts_files[rhosts_file_index]);
 220                 if (stat(buf, &st) >= 0)
 221                         break;
 222         }
 223         /* Switch back to privileged uid. */
 224         restore_uid();
 225
 226         /* Deny if The user has no .shosts or .rhosts file and there are no system-wide files. */
 227         if (!rhosts_files[rhosts_file_index] &&
 228             stat(_PATH_RHOSTS_EQUIV, &st) < 0 &&
 229             stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0)
 230                 return 0;
 231
 232         /* If not logging in as superuser, try /etc/hosts.equiv and shosts.equiv. */
 233         if (pw->pw_uid != 0) {
 234                 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr,
 235                     client_user, pw->pw_name)) {
 236                         auth_debug_add("Accepted for %.100s [%.100s] by /etc/hosts.equiv.",
 237                             hostname, ipaddr);
 238                         return 1;
 239                 }
 240                 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr,
 241                     client_user, pw->pw_name)) {
 242                         auth_debug_add("Accepted for %.100s [%.100s] by %.100s.",
 243                             hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV);
 244                         return 1;
 245                 }
 246         }
 247         /*
 248          * Check that the home directory is owned by root or the user, and is
 249          * not group or world writable.
 250          */
 251         if (stat(pw->pw_dir, &st) < 0) {
 252                 logit("Rhosts authentication refused for %.100s: "
 253                     "no home directory %.200s", pw->pw_name, pw->pw_dir);
 254                 auth_debug_add("Rhosts authentication refused for %.100s: "
 255                     "no home directory %.200s", pw->pw_name, pw->pw_dir);
 256                 return 0;
 257         }
 258         if (options.strict_modes &&
 259             ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
 260             (st.st_mode & 022) != 0)) {
 261                 logit("Rhosts authentication refused for %.100s: "
 262                     "bad ownership or modes for home directory.", pw->pw_name);
 263                 auth_debug_add("Rhosts authentication refused for %.100s: "
 264                     "bad ownership or modes for home directory.", pw->pw_name);
 265                 return 0;
 266         }
 267         /* Temporarily use the user's uid. */
 268         temporarily_use_uid(pw);
 269
 270         /* Check all .rhosts files (currently .shosts and .rhosts). */
 271         for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
 272             rhosts_file_index++) {
 273                 /* Check users .rhosts or .shosts. */
 274                 snprintf(buf, sizeof buf, "%.500s/%.100s",
 275                          pw->pw_dir, rhosts_files[rhosts_file_index]);
 276                 if (stat(buf, &st) < 0)
 277                         continue;
 278
 279                 /*
 280                  * Make sure that the file is either owned by the user or by
 281                  * root, and make sure it is not writable by anyone but the
 282                  * owner.  This is to help avoid novices accidentally
 283                  * allowing access to their account by anyone.
 284                  */
 285                 if (options.strict_modes &&
 286                     ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
 287                     (st.st_mode & 022) != 0)) {
 288                         logit("Rhosts authentication refused for %.100s: bad modes for %.200s",
 289                             pw->pw_name, buf);
 290                         auth_debug_add("Bad file modes for %.200s", buf);
 291                         continue;
 292                 }
 293                 /* Check if we have been configured to ignore .rhosts and .shosts files. */
 294                 if (options.ignore_rhosts) {
 295                         auth_debug_add("Server has been configured to ignore %.100s.",
 296                             rhosts_files[rhosts_file_index]);
 297                         continue;
 298                 }
 299                 /* Check if authentication is permitted by the file. */
 300                 if (check_rhosts_file(buf, hostname, ipaddr, client_user, pw->pw_name)) {
 301                         auth_debug_add("Accepted by %.100s.",
 302                             rhosts_files[rhosts_file_index]);
 303                         /* Restore the privileged uid. */
 304                         restore_uid();
 305                         auth_debug_add("Accepted host %s ip %s client_user %s server_user %s",
 306                                 hostname, ipaddr, client_user, pw->pw_name);
 307                         return 1;
 308                 }
 309         }
 310
 311         /* Restore the privileged uid. */
 312         restore_uid();
 313         return 0;
 314 }
 315
 316 int
 317 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
 318     const char *ipaddr)
 319 {
 320         int ret;
 321
 322         auth_debug_reset();
 323         ret = auth_rhosts2_raw(pw, client_user, hostname, ipaddr);
 324         if (!use_privsep)
 325                 auth_debug_send();
 326         return ret;
 327 }