crypto/openssh/auth-rhosts.c

   1 /* $OpenBSD: auth-rhosts.c,v 1.58 2024/05/17 00:30:23 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 #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
  50 /*
  51  * This function processes an rhosts-style file (.rhosts, .shosts, or
  52  * /etc/hosts.equiv).  This returns true if authentication can be granted
  53  * based on the file, and returns zero otherwise.
  54  */
  55
  56 static int
  57 check_rhosts_file(const char *filename, const char *hostname,
  58                   const char *ipaddr, const char *client_user,
  59                   const char *server_user)
  60 {
  61         FILE *f;
  62 #define RBUFLN 1024
  63         char buf[RBUFLN];/* Must not be larger than host, user, dummy below. */
  64         int fd;
  65         struct stat st;
  66
  67         /* Open the .rhosts file, deny if unreadable */
  68         if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1)
  69                 return 0;
  70         if (fstat(fd, &st) == -1) {
  71                 close(fd);
  72                 return 0;
  73         }
  74         if (!S_ISREG(st.st_mode)) {
  75                 logit("User %s hosts file %s is not a regular file",
  76                     server_user, filename);
  77                 close(fd);
  78                 return 0;
  79         }
  80         unset_nonblock(fd);
  81         if ((f = fdopen(fd, "r")) == NULL) {
  82                 close(fd);
  83                 return 0;
  84         }
  85         while (fgets(buf, sizeof(buf), f)) {
  86                 /* All three must have length >= buf to avoid overflows. */
  87                 char hostbuf[RBUFLN], userbuf[RBUFLN], dummy[RBUFLN];
  88                 char *host, *user, *cp;
  89                 int negated;
  90
  91                 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
  92                         ;
  93                 if (*cp == '#' || *cp == '\n' || !*cp)
  94                         continue;
  95
  96                 /*
  97                  * NO_PLUS is supported at least on OSF/1.  We skip it (we
  98                  * don't ever support the plus syntax).
  99                  */
 100                 if (strncmp(cp, "NO_PLUS", 7) == 0)
 101                         continue;
 102
 103                 /*
 104                  * This should be safe because each buffer is as big as the
 105                  * whole string, and thus cannot be overwritten.
 106                  */
 107                 switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf,
 108                     dummy)) {
 109                 case 0:
 110                         auth_debug_add("Found empty line in %.100s.", filename);
 111                         continue;
 112                 case 1:
 113                         /* Host name only. */
 114                         strlcpy(userbuf, server_user, sizeof(userbuf));
 115                         break;
 116                 case 2:
 117                         /* Got both host and user name. */
 118                         break;
 119                 case 3:
 120                         auth_debug_add("Found garbage in %.100s.", filename);
 121                         continue;
 122                 default:
 123                         /* Weird... */
 124                         continue;
 125                 }
 126
 127                 host = hostbuf;
 128                 user = userbuf;
 129                 negated = 0;
 130
 131                 /* Process negated host names, or positive netgroups. */
 132                 if (host[0] == '-') {
 133                         negated = 1;
 134                         host++;
 135                 } else if (host[0] == '+')
 136                         host++;
 137
 138                 if (user[0] == '-') {
 139                         negated = 1;
 140                         user++;
 141                 } else if (user[0] == '+')
 142                         user++;
 143
 144                 /* Check for empty host/user names (particularly '+'). */
 145                 if (!host[0] || !user[0]) {
 146                         /* We come here if either was '+' or '-'. */
 147                         auth_debug_add("Ignoring wild host/user names "
 148                             "in %.100s.", filename);
 149                         continue;
 150                 }
 151                 /* Verify that host name matches. */
 152                 if (host[0] == '@') {
 153                         if (!innetgr(host + 1, hostname, NULL, NULL) &&
 154                             !innetgr(host + 1, ipaddr, NULL, NULL))
 155                                 continue;
 156                 } else if (strcasecmp(host, hostname) &&
 157                     strcmp(host, ipaddr) != 0)
 158                         continue;       /* Different hostname. */
 159
 160                 /* Verify that user name matches. */
 161                 if (user[0] == '@') {
 162                         if (!innetgr(user + 1, NULL, client_user, NULL))
 163                                 continue;
 164                 } else if (strcmp(user, client_user) != 0)
 165                         continue;       /* Different username. */
 166
 167                 /* Found the user and host. */
 168                 fclose(f);
 169
 170                 /* If the entry was negated, deny access. */
 171                 if (negated) {
 172                         auth_debug_add("Matched negative entry in %.100s.",
 173                             filename);
 174                         return 0;
 175                 }
 176                 /* Accept authentication. */
 177                 return 1;
 178         }
 179
 180         /* Authentication using this file denied. */
 181         fclose(f);
 182         return 0;
 183 }
 184
 185 /*
 186  * Tries to authenticate the user using the .shosts or .rhosts file. Returns
 187  * true if authentication succeeds.  If ignore_rhosts is true, only
 188  * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
 189  */
 190 int
 191 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
 192     const char *ipaddr)
 193 {
 194         char *path = NULL;
 195         struct stat st;
 196         static const char * const rhosts_files[] = {".shosts", ".rhosts", NULL};
 197         u_int rhosts_file_index;
 198         int r;
 199
 200         debug2_f("clientuser %s hostname %s ipaddr %s",
 201             client_user, hostname, ipaddr);
 202
 203         /* Switch to the user's uid. */
 204         temporarily_use_uid(pw);
 205         /*
 206          * Quick check: if the user has no .shosts or .rhosts files and
 207          * no system hosts.equiv/shosts.equiv files exist then return
 208          * failure immediately without doing costly lookups from name
 209          * servers.
 210          */
 211         for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
 212             rhosts_file_index++) {
 213                 /* Check users .rhosts or .shosts. */
 214                 xasprintf(&path, "%s/%s",
 215                     pw->pw_dir, rhosts_files[rhosts_file_index]);
 216                 r = stat(path, &st);
 217                 free(path);
 218                 if (r >= 0)
 219                         break;
 220         }
 221         /* Switch back to privileged uid. */
 222         restore_uid();
 223
 224         /*
 225          * Deny if The user has no .shosts or .rhosts file and there
 226          * are no system-wide files.
 227          */
 228         if (!rhosts_files[rhosts_file_index] &&
 229             stat(_PATH_RHOSTS_EQUIV, &st) == -1 &&
 230             stat(_PATH_SSH_HOSTS_EQUIV, &st) == -1) {
 231                 debug3_f("no hosts access files exist");
 232                 return 0;
 233         }
 234
 235         /*
 236          * If not logging in as superuser, try /etc/hosts.equiv and
 237          * shosts.equiv.
 238          */
 239         if (pw->pw_uid == 0)
 240                 debug3_f("root user, ignoring system hosts files");
 241         else {
 242                 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr,
 243                     client_user, pw->pw_name)) {
 244                         auth_debug_add("Accepted for %.100s [%.100s] by "
 245                             "/etc/hosts.equiv.", hostname, ipaddr);
 246                         return 1;
 247                 }
 248                 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr,
 249                     client_user, pw->pw_name)) {
 250                         auth_debug_add("Accepted for %.100s [%.100s] by "
 251                             "%.100s.", hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV);
 252                         return 1;
 253                 }
 254         }
 255
 256         /*
 257          * Check that the home directory is owned by root or the user, and is
 258          * not group or world writable.
 259          */
 260         if (stat(pw->pw_dir, &st) == -1) {
 261                 logit("Rhosts authentication refused for %.100s: "
 262                     "no home directory %.200s", pw->pw_name, pw->pw_dir);
 263                 auth_debug_add("Rhosts authentication refused for %.100s: "
 264                     "no home directory %.200s", pw->pw_name, pw->pw_dir);
 265                 return 0;
 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: "
 271                     "bad ownership or modes for home directory.", pw->pw_name);
 272                 auth_debug_add("Rhosts authentication refused for %.100s: "
 273                     "bad ownership or modes for home directory.", pw->pw_name);
 274                 return 0;
 275         }
 276         /* Temporarily use the user's uid. */
 277         temporarily_use_uid(pw);
 278
 279         /* Check all .rhosts files (currently .shosts and .rhosts). */
 280         for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
 281             rhosts_file_index++) {
 282                 /* Check users .rhosts or .shosts. */
 283                 xasprintf(&path, "%s/%s",
 284                     pw->pw_dir, rhosts_files[rhosts_file_index]);
 285                 if (stat(path, &st) == -1) {
 286                         debug3_f("stat %s: %s", path, strerror(errno));
 287                         free(path);
 288                         continue;
 289                 }
 290
 291                 /*
 292                  * Make sure that the file is either owned by the user or by
 293                  * root, and make sure it is not writable by anyone but the
 294                  * owner.  This is to help avoid novices accidentally
 295                  * allowing access to their account by anyone.
 296                  */
 297                 if (options.strict_modes &&
 298                     ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
 299                     (st.st_mode & 022) != 0)) {
 300                         logit("Rhosts authentication refused for %.100s: "
 301                             "bad modes for %.200s", pw->pw_name, path);
 302                         auth_debug_add("Bad file modes for %.200s", path);
 303                         free(path);
 304                         continue;
 305                 }
 306                 /*
 307                  * Check if we have been configured to ignore .rhosts
 308                  * and .shosts files.
 309                  */
 310                 if (options.ignore_rhosts == IGNORE_RHOSTS_YES ||
 311                     (options.ignore_rhosts == IGNORE_RHOSTS_SHOSTS &&
 312                     strcmp(rhosts_files[rhosts_file_index], ".shosts") != 0)) {
 313                         auth_debug_add("Server has been configured to "
 314                             "ignore %.100s.", rhosts_files[rhosts_file_index]);
 315                         free(path);
 316                         continue;
 317                 }
 318                 /* Check if authentication is permitted by the file. */
 319                 if (check_rhosts_file(path, hostname, ipaddr,
 320                     client_user, pw->pw_name)) {
 321                         auth_debug_add("Accepted by %.100s.",
 322                             rhosts_files[rhosts_file_index]);
 323                         /* Restore the privileged uid. */
 324                         restore_uid();
 325                         auth_debug_add("Accepted host %s ip %s client_user "
 326                             "%s server_user %s", hostname, ipaddr,
 327                             client_user, pw->pw_name);
 328                         free(path);
 329                         return 1;
 330                 }
 331                 free(path);
 332         }
 333
 334         /* Restore the privileged uid. */
 335         restore_uid();
 336         return 0;
 337 }