crypto/openssh/auth-rhosts.c

   1 /* $OpenBSD: auth-rhosts.c,v 1.47 2016/03/07 19:02:43 djm 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 "uidswap.h"
  34 #include "pathnames.h"
  35 #include "log.h"
  36 #include "misc.h"
  37 #include "buffer.h" /* XXX */
  38 #include "key.h" /* XXX */
  39 #include "servconf.h"
  40 #include "canohost.h"
  41 #include "sshkey.h"
  42 #include "hostfile.h"
  43 #include "auth.h"
  44
  45 /* import */
  46 extern ServerOptions options;
  47 extern int use_privsep;
  48
  49 /*
  50  * This function processes an rhosts-style file (.rhosts, .shosts, or
  51  * /etc/hosts.equiv).  This returns true if authentication can be granted
  52  * based on the file, and returns zero otherwise.
  53  */
  54
  55 static int
  56 check_rhosts_file(const char *filename, const char *hostname,
  57                   const char *ipaddr, const char *client_user,
  58                   const char *server_user)
  59 {
  60         FILE *f;
  61 #define RBUFLN 1024
  62         char buf[RBUFLN];/* Must not be larger than host, user, dummy below. */
  63         int fd;
  64         struct stat st;
  65
  66         /* Open the .rhosts file, deny if unreadable */
  67         if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1)
  68                 return 0;
  69         if (fstat(fd, &st) == -1) {
  70                 close(fd);
  71                 return 0;
  72         }
  73         if (!S_ISREG(st.st_mode)) {
  74                 logit("User %s hosts file %s is not a regular file",
  75                     server_user, filename);
  76                 close(fd);
  77                 return 0;
  78         }
  79         unset_nonblock(fd);
  80         if ((f = fdopen(fd, "r")) == NULL) {
  81                 close(fd);
  82                 return 0;
  83         }
  84         while (fgets(buf, sizeof(buf), f)) {
  85                 /* All three must have length >= buf to avoid overflows. */
  86                 char hostbuf[RBUFLN], userbuf[RBUFLN], dummy[RBUFLN];
  87                 char *host, *user, *cp;
  88                 int negated;
  89
  90                 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
  91                         ;
  92                 if (*cp == '#' || *cp == '\n' || !*cp)
  93                         continue;
  94
  95                 /*
  96                  * NO_PLUS is supported at least on OSF/1.  We skip it (we
  97                  * don't ever support the plus syntax).
  98                  */
  99                 if (strncmp(cp, "NO_PLUS", 7) == 0)
 100                         continue;
 101
 102                 /*
 103                  * This should be safe because each buffer is as big as the
 104                  * whole string, and thus cannot be overwritten.
 105                  */
 106                 switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf,
 107                     dummy)) {
 108                 case 0:
 109                         auth_debug_add("Found empty line in %.100s.", filename);
 110                         continue;
 111                 case 1:
 112                         /* Host name only. */
 113                         strlcpy(userbuf, server_user, sizeof(userbuf));
 114                         break;
 115                 case 2:
 116                         /* Got both host and user name. */
 117                         break;
 118                 case 3:
 119                         auth_debug_add("Found garbage in %.100s.", filename);
 120                         continue;
 121                 default:
 122                         /* Weird... */
 123                         continue;
 124                 }
 125
 126                 host = hostbuf;
 127                 user = userbuf;
 128                 negated = 0;
 129
 130                 /* Process negated host names, or positive netgroups. */
 131                 if (host[0] == '-') {
 132                         negated = 1;
 133                         host++;
 134                 } else if (host[0] == '+')
 135                         host++;
 136
 137                 if (user[0] == '-') {
 138                         negated = 1;
 139                         user++;
 140                 } else if (user[0] == '+')
 141                         user++;
 142
 143                 /* Check for empty host/user names (particularly '+'). */
 144                 if (!host[0] || !user[0]) {
 145                         /* We come here if either was '+' or '-'. */
 146                         auth_debug_add("Ignoring wild host/user names "
 147                             "in %.100s.", filename);
 148                         continue;
 149                 }
 150                 /* Verify that host name matches. */
 151                 if (host[0] == '@') {
 152                         if (!innetgr(host + 1, hostname, NULL, NULL) &&
 153                             !innetgr(host + 1, ipaddr, NULL, NULL))
 154                                 continue;
 155                 } else if (strcasecmp(host, hostname) &&
 156                     strcmp(host, ipaddr) != 0)
 157                         continue;       /* Different hostname. */
 158
 159                 /* Verify that user name matches. */
 160                 if (user[0] == '@') {
 161                         if (!innetgr(user + 1, NULL, client_user, NULL))
 162                                 continue;
 163                 } else if (strcmp(user, client_user) != 0)
 164                         continue;       /* Different username. */
 165
 166                 /* Found the user and host. */
 167                 fclose(f);
 168
 169                 /* If the entry was negated, deny access. */
 170                 if (negated) {
 171                         auth_debug_add("Matched negative entry in %.100s.",
 172                             filename);
 173                         return 0;
 174                 }
 175                 /* Accept authentication. */
 176                 return 1;
 177         }
 178
 179         /* Authentication using this file denied. */
 180         fclose(f);
 181         return 0;
 182 }
 183
 184 /*
 185  * Tries to authenticate the user using the .shosts or .rhosts file. Returns
 186  * true if authentication succeeds.  If ignore_rhosts is true, only
 187  * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
 188  */
 189
 190 int
 191 auth_rhosts(struct passwd *pw, const char *client_user)
 192 {
 193         struct ssh *ssh = active_state; /* XXX */
 194         const char *hostname, *ipaddr;
 195
 196         hostname = auth_get_canonical_hostname(ssh, options.use_dns);
 197         ipaddr = ssh_remote_ipaddr(ssh);
 198         return auth_rhosts2(pw, client_user, hostname, ipaddr);
 199 }
 200
 201 static int
 202 auth_rhosts2_raw(struct passwd *pw, const char *client_user, const char *hostname,
 203     const char *ipaddr)
 204 {
 205         char buf[1024];
 206         struct stat st;
 207         static const char *rhosts_files[] = {".shosts", ".rhosts", NULL};
 208         u_int rhosts_file_index;
 209
 210         debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s",
 211             client_user, hostname, ipaddr);
 212
 213         /* Switch to the user's uid. */
 214         temporarily_use_uid(pw);
 215         /*
 216          * Quick check: if the user has no .shosts or .rhosts files and
 217          * no system hosts.equiv/shosts.equiv files exist then return
 218          * failure immediately without doing costly lookups from name
 219          * servers.
 220          */
 221         for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
 222             rhosts_file_index++) {
 223                 /* Check users .rhosts or .shosts. */
 224                 snprintf(buf, sizeof buf, "%.500s/%.100s",
 225                          pw->pw_dir, rhosts_files[rhosts_file_index]);
 226                 if (stat(buf, &st) >= 0)
 227                         break;
 228         }
 229         /* Switch back to privileged uid. */
 230         restore_uid();
 231
 232         /*
 233          * Deny if The user has no .shosts or .rhosts file and there
 234          * are no system-wide files.
 235          */
 236         if (!rhosts_files[rhosts_file_index] &&
 237             stat(_PATH_RHOSTS_EQUIV, &st) < 0 &&
 238             stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0) {
 239                 debug3("%s: no hosts access files exist", __func__);
 240                 return 0;
 241         }
 242
 243         /*
 244          * If not logging in as superuser, try /etc/hosts.equiv and
 245          * shosts.equiv.
 246          */
 247         if (pw->pw_uid == 0)
 248                 debug3("%s: root user, ignoring system hosts files", __func__);
 249         else {
 250                 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr,
 251                     client_user, pw->pw_name)) {
 252                         auth_debug_add("Accepted for %.100s [%.100s] by "
 253                             "/etc/hosts.equiv.", hostname, ipaddr);
 254                         return 1;
 255                 }
 256                 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr,
 257                     client_user, pw->pw_name)) {
 258                         auth_debug_add("Accepted for %.100s [%.100s] by "
 259                             "%.100s.", hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV);
 260                         return 1;
 261                 }
 262         }
 263
 264         /*
 265          * Check that the home directory is owned by root or the user, and is
 266          * not group or world writable.
 267          */
 268         if (stat(pw->pw_dir, &st) < 0) {
 269                 logit("Rhosts authentication refused for %.100s: "
 270                     "no home directory %.200s", pw->pw_name, pw->pw_dir);
 271                 auth_debug_add("Rhosts authentication refused for %.100s: "
 272                     "no home directory %.200s", pw->pw_name, pw->pw_dir);
 273                 return 0;
 274         }
 275         if (options.strict_modes &&
 276             ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
 277             (st.st_mode & 022) != 0)) {
 278                 logit("Rhosts authentication refused for %.100s: "
 279                     "bad ownership or modes for home directory.", pw->pw_name);
 280                 auth_debug_add("Rhosts authentication refused for %.100s: "
 281                     "bad ownership or modes for home directory.", pw->pw_name);
 282                 return 0;
 283         }
 284         /* Temporarily use the user's uid. */
 285         temporarily_use_uid(pw);
 286
 287         /* Check all .rhosts files (currently .shosts and .rhosts). */
 288         for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
 289             rhosts_file_index++) {
 290                 /* Check users .rhosts or .shosts. */
 291                 snprintf(buf, sizeof buf, "%.500s/%.100s",
 292                          pw->pw_dir, rhosts_files[rhosts_file_index]);
 293                 if (stat(buf, &st) < 0)
 294                         continue;
 295
 296                 /*
 297                  * Make sure that the file is either owned by the user or by
 298                  * root, and make sure it is not writable by anyone but the
 299                  * owner.  This is to help avoid novices accidentally
 300                  * allowing access to their account by anyone.
 301                  */
 302                 if (options.strict_modes &&
 303                     ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
 304                     (st.st_mode & 022) != 0)) {
 305                         logit("Rhosts authentication refused for %.100s: bad modes for %.200s",
 306                             pw->pw_name, buf);
 307                         auth_debug_add("Bad file modes for %.200s", buf);
 308                         continue;
 309                 }
 310                 /*
 311                  * Check if we have been configured to ignore .rhosts
 312                  * and .shosts files.
 313                  */
 314                 if (options.ignore_rhosts) {
 315                         auth_debug_add("Server has been configured to "
 316                             "ignore %.100s.", rhosts_files[rhosts_file_index]);
 317                         continue;
 318                 }
 319                 /* Check if authentication is permitted by the file. */
 320                 if (check_rhosts_file(buf, 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                         return 1;
 330                 }
 331         }
 332
 333         /* Restore the privileged uid. */
 334         restore_uid();
 335         return 0;
 336 }
 337
 338 int
 339 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
 340     const char *ipaddr)
 341 {
 342        return auth_rhosts2_raw(pw, client_user, hostname, ipaddr);
 343 }