crypto/openssh/auth-rhosts.c

   1 /* $OpenBSD: auth-rhosts.c,v 1.57 2022/12/09 00:17:40 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 #include <errno.h>
  23 #include <fcntl.h>
  24 #ifdef HAVE_NETGROUP_H
  25 # include <netgroup.h>
  26 #endif
  27 #include <pwd.h>
  28 #include <stdio.h>
  29 #include <string.h>
  30 #include <stdarg.h>
  31 #include <stdlib.h>
  32 #include <unistd.h>
  33
  34 #include "packet.h"
  35 #include "uidswap.h"
  36 #include "pathnames.h"
  37 #include "log.h"
  38 #include "misc.h"
  39 #include "xmalloc.h"
  40 #include "sshbuf.h"
  41 #include "sshkey.h"
  42 #include "servconf.h"
  43 #include "canohost.h"
  44 #include "hostfile.h"
  45 #include "auth.h"
  46
  47 /* import */
  48 extern ServerOptions options;
  49 extern int use_privsep;
  50
  51 /*
  52  * This function processes an rhosts-style file (.rhosts, .shosts, or
  53  * /etc/hosts.equiv).  This returns true if authentication can be granted
  54  * based on the file, and returns zero otherwise.
  55  */
  56
  57 static int
  58 check_rhosts_file(const char *filename, const char *hostname,
  59                   const char *ipaddr, const char *client_user,
  60                   const char *server_user)
  61 {
  62         FILE *f;
  63 #define RBUFLN 1024
  64         char buf[RBUFLN];/* Must not be larger than host, user, dummy below. */
  65         int fd;
  66         struct stat st;
  67
  68         /* Open the .rhosts file, deny if unreadable */
  69         if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1)
  70                 return 0;
  71         if (fstat(fd, &st) == -1) {
  72                 close(fd);
  73                 return 0;
  74         }
  75         if (!S_ISREG(st.st_mode)) {
  76                 logit("User %s hosts file %s is not a regular file",
  77                     server_user, filename);
  78                 close(fd);
  79                 return 0;
  80         }
  81         unset_nonblock(fd);
  82         if ((f = fdopen(fd, "r")) == NULL) {
  83                 close(fd);
  84                 return 0;
  85         }
  86         while (fgets(buf, sizeof(buf), f)) {
  87                 /* All three must have length >= buf to avoid overflows. */
  88                 char hostbuf[RBUFLN], userbuf[RBUFLN], dummy[RBUFLN];
  89                 char *host, *user, *cp;
  90                 int negated;
  91
  92                 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
  93                         ;
  94                 if (*cp == '#' || *cp == '\n' || !*cp)
  95                         continue;
  96
  97                 /*
  98                  * NO_PLUS is supported at least on OSF/1.  We skip it (we
  99                  * don't ever support the plus syntax).
 100                  */
 101                 if (strncmp(cp, "NO_PLUS", 7) == 0)
 102                         continue;
 103
 104                 /*
 105                  * This should be safe because each buffer is as big as the
 106                  * whole string, and thus cannot be overwritten.
 107                  */
 108                 switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf,
 109                     dummy)) {
 110                 case 0:
 111                         auth_debug_add("Found empty line in %.100s.", filename);
 112                         continue;
 113                 case 1:
 114                         /* Host name only. */
 115                         strlcpy(userbuf, server_user, sizeof(userbuf));
 116                         break;
 117                 case 2:
 118                         /* Got both host and user name. */
 119                         break;
 120                 case 3:
 121                         auth_debug_add("Found garbage in %.100s.", filename);
 122                         continue;
 123                 default:
 124                         /* Weird... */
 125                         continue;
 126                 }
 127
 128                 host = hostbuf;
 129                 user = userbuf;
 130                 negated = 0;
 131
 132                 /* Process negated host names, or positive netgroups. */
 133                 if (host[0] == '-') {
 134                         negated = 1;
 135                         host++;
 136                 } else if (host[0] == '+')
 137                         host++;
 138
 139                 if (user[0] == '-') {
 140                         negated = 1;
 141                         user++;
 142                 } else if (user[0] == '+')
 143                         user++;
 144
 145                 /* Check for empty host/user names (particularly '+'). */
 146                 if (!host[0] || !user[0]) {
 147                         /* We come here if either was '+' or '-'. */
 148                         auth_debug_add("Ignoring wild host/user names "
 149                             "in %.100s.", filename);
 150                         continue;
 151                 }
 152                 /* Verify that host name matches. */
 153                 if (host[0] == '@') {
 154                         if (!innetgr(host + 1, hostname, NULL, NULL) &&
 155                             !innetgr(host + 1, ipaddr, NULL, NULL))
 156                                 continue;
 157                 } else if (strcasecmp(host, hostname) &&
 158                     strcmp(host, ipaddr) != 0)
 159                         continue;       /* Different hostname. */
 160
 161                 /* Verify that user name matches. */
 162                 if (user[0] == '@') {
 163                         if (!innetgr(user + 1, NULL, client_user, NULL))
 164                                 continue;
 165                 } else if (strcmp(user, client_user) != 0)
 166                         continue;       /* Different username. */
 167
 168                 /* Found the user and host. */
 169                 fclose(f);
 170
 171                 /* If the entry was negated, deny access. */
 172                 if (negated) {
 173                         auth_debug_add("Matched negative entry in %.100s.",
 174                             filename);
 175                         return 0;
 176                 }
 177                 /* Accept authentication. */
 178                 return 1;
 179         }
 180
 181         /* Authentication using this file denied. */
 182         fclose(f);
 183         return 0;
 184 }
 185
 186 /*
 187  * Tries to authenticate the user using the .shosts or .rhosts file. Returns
 188  * true if authentication succeeds.  If ignore_rhosts is true, only
 189  * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
 190  */
 191 int
 192 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
 193     const char *ipaddr)
 194 {
 195         char *path = NULL;
 196         struct stat st;
 197         static const char * const rhosts_files[] = {".shosts", ".rhosts", NULL};
 198         u_int rhosts_file_index;
 199         int r;
 200
 201         debug2_f("clientuser %s hostname %s ipaddr %s",
 202             client_user, hostname, ipaddr);
 203
 204         /* Switch to the user's uid. */
 205         temporarily_use_uid(pw);
 206         /*
 207          * Quick check: if the user has no .shosts or .rhosts files and
 208          * no system hosts.equiv/shosts.equiv files exist then return
 209          * failure immediately without doing costly lookups from name
 210          * servers.
 211          */
 212         for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
 213             rhosts_file_index++) {
 214                 /* Check users .rhosts or .shosts. */
 215                 xasprintf(&path, "%s/%s",
 216                     pw->pw_dir, rhosts_files[rhosts_file_index]);
 217                 r = stat(path, &st);
 218                 free(path);
 219                 if (r >= 0)
 220                         break;
 221         }
 222         /* Switch back to privileged uid. */
 223         restore_uid();
 224
 225         /*
 226          * Deny if The user has no .shosts or .rhosts file and there
 227          * are no system-wide files.
 228          */
 229         if (!rhosts_files[rhosts_file_index] &&
 230             stat(_PATH_RHOSTS_EQUIV, &st) == -1 &&
 231             stat(_PATH_SSH_HOSTS_EQUIV, &st) == -1) {
 232                 debug3_f("no hosts access files exist");
 233                 return 0;
 234         }
 235
 236         /*
 237          * If not logging in as superuser, try /etc/hosts.equiv and
 238          * shosts.equiv.
 239          */
 240         if (pw->pw_uid == 0)
 241                 debug3_f("root user, ignoring system hosts files");
 242         else {
 243                 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr,
 244                     client_user, pw->pw_name)) {
 245                         auth_debug_add("Accepted for %.100s [%.100s] by "
 246                             "/etc/hosts.equiv.", hostname, ipaddr);
 247                         return 1;
 248                 }
 249                 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr,
 250                     client_user, pw->pw_name)) {
 251                         auth_debug_add("Accepted for %.100s [%.100s] by "
 252                             "%.100s.", hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV);
 253                         return 1;
 254                 }
 255         }
 256
 257         /*
 258          * Check that the home directory is owned by root or the user, and is
 259          * not group or world writable.
 260          */
 261         if (stat(pw->pw_dir, &st) == -1) {
 262                 logit("Rhosts authentication refused for %.100s: "
 263                     "no home directory %.200s", pw->pw_name, pw->pw_dir);
 264                 auth_debug_add("Rhosts authentication refused for %.100s: "
 265                     "no home directory %.200s", pw->pw_name, pw->pw_dir);
 266                 return 0;
 267         }
 268         if (options.strict_modes &&
 269             ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
 270             (st.st_mode & 022) != 0)) {
 271                 logit("Rhosts authentication refused for %.100s: "
 272                     "bad ownership or modes for home directory.", pw->pw_name);
 273                 auth_debug_add("Rhosts authentication refused for %.100s: "
 274                     "bad ownership or modes for home directory.", pw->pw_name);
 275                 return 0;
 276         }
 277         /* Temporarily use the user's uid. */
 278         temporarily_use_uid(pw);
 279
 280         /* Check all .rhosts files (currently .shosts and .rhosts). */
 281         for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
 282             rhosts_file_index++) {
 283                 /* Check users .rhosts or .shosts. */
 284                 xasprintf(&path, "%s/%s",
 285                     pw->pw_dir, rhosts_files[rhosts_file_index]);
 286                 if (stat(path, &st) == -1) {
 287                         debug3_f("stat %s: %s", path, strerror(errno));
 288                         free(path);
 289                         continue;
 290                 }
 291
 292                 /*
 293                  * Make sure that the file is either owned by the user or by
 294                  * root, and make sure it is not writable by anyone but the
 295                  * owner.  This is to help avoid novices accidentally
 296                  * allowing access to their account by anyone.
 297                  */
 298                 if (options.strict_modes &&
 299                     ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
 300                     (st.st_mode & 022) != 0)) {
 301                         logit("Rhosts authentication refused for %.100s: "
 302                             "bad modes for %.200s", pw->pw_name, path);
 303                         auth_debug_add("Bad file modes for %.200s", path);
 304                         free(path);
 305                         continue;
 306                 }
 307                 /*
 308                  * Check if we have been configured to ignore .rhosts
 309                  * and .shosts files.
 310                  */
 311                 if (options.ignore_rhosts == IGNORE_RHOSTS_YES ||
 312                     (options.ignore_rhosts == IGNORE_RHOSTS_SHOSTS &&
 313                     strcmp(rhosts_files[rhosts_file_index], ".shosts") != 0)) {
 314                         auth_debug_add("Server has been configured to "
 315                             "ignore %.100s.", rhosts_files[rhosts_file_index]);
 316                         free(path);
 317                         continue;
 318                 }
 319                 /* Check if authentication is permitted by the file. */
 320                 if (check_rhosts_file(path, hostname, ipaddr,
 321                     client_user, pw->pw_name)) {
 322                         auth_debug_add("Accepted by %.100s.",
 323                             rhosts_files[rhosts_file_index]);
 324                         /* Restore the privileged uid. */
 325                         restore_uid();
 326                         auth_debug_add("Accepted host %s ip %s client_user "
 327                             "%s server_user %s", hostname, ipaddr,
 328                             client_user, pw->pw_name);
 329                         free(path);
 330                         return 1;
 331                 }
 332                 free(path);
 333         }
 334
 335         /* Restore the privileged uid. */
 336         restore_uid();
 337         return 0;
 338 }