auth-rhosts.c

   1 /* $OpenBSD: auth-rhosts.c,v 1.41 2006/08/03 03:34:41 deraadt 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
  30 #include "packet.h"
  31 #include "buffer.h"
  32 #include "uidswap.h"
  33 #include "pathnames.h"
  34 #include "log.h"
  35 #include "servconf.h"
  36 #include "canohost.h"
  37 #include "key.h"
  38 #include "hostfile.h"
  39 #include "auth.h"
  40
  41 /* import */
  42 extern ServerOptions options;
  43 extern int use_privsep;
  44
  45 /*
  46  * This function processes an rhosts-style file (.rhosts, .shosts, or
  47  * /etc/hosts.equiv).  This returns true if authentication can be granted
  48  * based on the file, and returns zero otherwise.
  49  */
  50
  51 static int
  52 check_rhosts_file(const char *filename, const char *hostname,
  53                   const char *ipaddr, const char *client_user,
  54                   const char *server_user)
  55 {
  56         FILE *f;
  57         char buf[1024]; /* Must not be larger than host, user, dummy below. */
  58
  59         /* Open the .rhosts file, deny if unreadable */
  60         f = fopen(filename, "r");
  61         if (!f)
  62                 return 0;
  63
  64         while (fgets(buf, sizeof(buf), f)) {
  65                 /* All three must be at least as big as buf to avoid overflows. */
  66                 char hostbuf[1024], userbuf[1024], dummy[1024], *host, *user, *cp;
  67                 int negated;
  68
  69                 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
  70                         ;
  71                 if (*cp == '#' || *cp == '\n' || !*cp)
  72                         continue;
  73
  74                 /*
  75                  * NO_PLUS is supported at least on OSF/1.  We skip it (we
  76                  * don't ever support the plus syntax).
  77                  */
  78                 if (strncmp(cp, "NO_PLUS", 7) == 0)
  79                         continue;
  80
  81                 /*
  82                  * This should be safe because each buffer is as big as the
  83                  * whole string, and thus cannot be overwritten.
  84                  */
  85                 switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf,
  86                     dummy)) {
  87                 case 0:
  88                         auth_debug_add("Found empty line in %.100s.", filename);
  89                         continue;
  90                 case 1:
  91                         /* Host name only. */
  92                         strlcpy(userbuf, server_user, sizeof(userbuf));
  93                         break;
  94                 case 2:
  95                         /* Got both host and user name. */
  96                         break;
  97                 case 3:
  98                         auth_debug_add("Found garbage in %.100s.", filename);
  99                         continue;
 100                 default:
 101                         /* Weird... */
 102                         continue;
 103                 }
 104
 105                 host = hostbuf;
 106                 user = userbuf;
 107                 negated = 0;
 108
 109                 /* Process negated host names, or positive netgroups. */
 110                 if (host[0] == '-') {
 111                         negated = 1;
 112                         host++;
 113                 } else if (host[0] == '+')
 114                         host++;
 115
 116                 if (user[0] == '-') {
 117                         negated = 1;
 118                         user++;
 119                 } else if (user[0] == '+')
 120                         user++;
 121
 122                 /* Check for empty host/user names (particularly '+'). */
 123                 if (!host[0] || !user[0]) {
 124                         /* We come here if either was '+' or '-'. */
 125                         auth_debug_add("Ignoring wild host/user names in %.100s.",
 126                             filename);
 127                         continue;
 128                 }
 129                 /* Verify that host name matches. */
 130                 if (host[0] == '@') {
 131                         if (!innetgr(host + 1, hostname, NULL, NULL) &&
 132                             !innetgr(host + 1, ipaddr, NULL, NULL))
 133                                 continue;
 134                 } else if (strcasecmp(host, hostname) && strcmp(host, ipaddr) != 0)
 135                         continue;       /* Different hostname. */
 136
 137                 /* Verify that user name matches. */
 138                 if (user[0] == '@') {
 139                         if (!innetgr(user + 1, NULL, client_user, NULL))
 140                                 continue;
 141                 } else if (strcmp(user, client_user) != 0)
 142                         continue;       /* Different username. */
 143
 144                 /* Found the user and host. */
 145                 fclose(f);
 146
 147                 /* If the entry was negated, deny access. */
 148                 if (negated) {
 149                         auth_debug_add("Matched negative entry in %.100s.",
 150                             filename);
 151                         return 0;
 152                 }
 153                 /* Accept authentication. */
 154                 return 1;
 155         }
 156
 157         /* Authentication using this file denied. */
 158         fclose(f);
 159         return 0;
 160 }
 161
 162 /*
 163  * Tries to authenticate the user using the .shosts or .rhosts file. Returns
 164  * true if authentication succeeds.  If ignore_rhosts is true, only
 165  * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
 166  */
 167
 168 int
 169 auth_rhosts(struct passwd *pw, const char *client_user)
 170 {
 171         const char *hostname, *ipaddr;
 172
 173         hostname = get_canonical_hostname(options.use_dns);
 174         ipaddr = get_remote_ipaddr();
 175         return auth_rhosts2(pw, client_user, hostname, ipaddr);
 176 }
 177
 178 static int
 179 auth_rhosts2_raw(struct passwd *pw, const char *client_user, const char *hostname,
 180     const char *ipaddr)
 181 {
 182         char buf[1024];
 183         struct stat st;
 184         static const char *rhosts_files[] = {".shosts", ".rhosts", NULL};
 185         u_int rhosts_file_index;
 186
 187         debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s",
 188             client_user, hostname, ipaddr);
 189
 190         /* Switch to the user's uid. */
 191         temporarily_use_uid(pw);
 192         /*
 193          * Quick check: if the user has no .shosts or .rhosts files, return
 194          * failure immediately without doing costly lookups from name
 195          * servers.
 196          */
 197         for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
 198             rhosts_file_index++) {
 199                 /* Check users .rhosts or .shosts. */
 200                 snprintf(buf, sizeof buf, "%.500s/%.100s",
 201                          pw->pw_dir, rhosts_files[rhosts_file_index]);
 202                 if (stat(buf, &st) >= 0)
 203                         break;
 204         }
 205         /* Switch back to privileged uid. */
 206         restore_uid();
 207
 208         /* Deny if The user has no .shosts or .rhosts file and there are no system-wide files. */
 209         if (!rhosts_files[rhosts_file_index] &&
 210             stat(_PATH_RHOSTS_EQUIV, &st) < 0 &&
 211             stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0)
 212                 return 0;
 213
 214         /* If not logging in as superuser, try /etc/hosts.equiv and shosts.equiv. */
 215         if (pw->pw_uid != 0) {
 216                 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr,
 217                     client_user, pw->pw_name)) {
 218                         auth_debug_add("Accepted for %.100s [%.100s] by /etc/hosts.equiv.",
 219                             hostname, ipaddr);
 220                         return 1;
 221                 }
 222                 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr,
 223                     client_user, pw->pw_name)) {
 224                         auth_debug_add("Accepted for %.100s [%.100s] by %.100s.",
 225                             hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV);
 226                         return 1;
 227                 }
 228         }
 229         /*
 230          * Check that the home directory is owned by root or the user, and is
 231          * not group or world writable.
 232          */
 233         if (stat(pw->pw_dir, &st) < 0) {
 234                 logit("Rhosts authentication refused for %.100s: "
 235                     "no home directory %.200s", pw->pw_name, pw->pw_dir);
 236                 auth_debug_add("Rhosts authentication refused for %.100s: "
 237                     "no home directory %.200s", pw->pw_name, pw->pw_dir);
 238                 return 0;
 239         }
 240         if (options.strict_modes &&
 241             ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
 242             (st.st_mode & 022) != 0)) {
 243                 logit("Rhosts authentication refused for %.100s: "
 244                     "bad ownership or modes for home directory.", pw->pw_name);
 245                 auth_debug_add("Rhosts authentication refused for %.100s: "
 246                     "bad ownership or modes for home directory.", pw->pw_name);
 247                 return 0;
 248         }
 249         /* Temporarily use the user's uid. */
 250         temporarily_use_uid(pw);
 251
 252         /* Check all .rhosts files (currently .shosts and .rhosts). */
 253         for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
 254             rhosts_file_index++) {
 255                 /* Check users .rhosts or .shosts. */
 256                 snprintf(buf, sizeof buf, "%.500s/%.100s",
 257                          pw->pw_dir, rhosts_files[rhosts_file_index]);
 258                 if (stat(buf, &st) < 0)
 259                         continue;
 260
 261                 /*
 262                  * Make sure that the file is either owned by the user or by
 263                  * root, and make sure it is not writable by anyone but the
 264                  * owner.  This is to help avoid novices accidentally
 265                  * allowing access to their account by anyone.
 266                  */
 267                 if (options.strict_modes &&
 268                     ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
 269                     (st.st_mode & 022) != 0)) {
 270                         logit("Rhosts authentication refused for %.100s: bad modes for %.200s",
 271                             pw->pw_name, buf);
 272                         auth_debug_add("Bad file modes for %.200s", buf);
 273                         continue;
 274                 }
 275                 /* Check if we have been configured to ignore .rhosts and .shosts files. */
 276                 if (options.ignore_rhosts) {
 277                         auth_debug_add("Server has been configured to ignore %.100s.",
 278                             rhosts_files[rhosts_file_index]);
 279                         continue;
 280                 }
 281                 /* Check if authentication is permitted by the file. */
 282                 if (check_rhosts_file(buf, hostname, ipaddr, client_user, pw->pw_name)) {
 283                         auth_debug_add("Accepted by %.100s.",
 284                             rhosts_files[rhosts_file_index]);
 285                         /* Restore the privileged uid. */
 286                         restore_uid();
 287                         auth_debug_add("Accepted host %s ip %s client_user %s server_user %s",
 288                                 hostname, ipaddr, client_user, pw->pw_name);
 289                         return 1;
 290                 }
 291         }
 292
 293         /* Restore the privileged uid. */
 294         restore_uid();
 295         return 0;
 296 }
 297
 298 int
 299 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
 300     const char *ipaddr)
 301 {
 302         int ret;
 303
 304         auth_debug_reset();
 305         ret = auth_rhosts2_raw(pw, client_user, hostname, ipaddr);
 306         if (!use_privsep)
 307                 auth_debug_send();
 308         return ret;
 309 }