2 * Author: Tatu Ylonen <ylo@cs.hut.fi>
3 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5 * Rhosts authentication. This file contains code to check whether to admit
6 * the login based on rhosts authentication. This file also processes
9 * As far as I am concerned, the code I have written for this software
10 * can be used freely for any purpose. Any derived versions of this
11 * software must be clearly marked as such, and if the derived work is
12 * incompatible with the protocol description in the RFC file, it must be
13 * called by a name other than "ssh" or "Secure Shell".
17 RCSID("$OpenBSD: auth-rhosts.c,v 1.24 2001/06/23 15:12:17 itojun Exp $");
22 #include "pathnames.h"
29 extern ServerOptions options;
32 * This function processes an rhosts-style file (.rhosts, .shosts, or
33 * /etc/hosts.equiv). This returns true if authentication can be granted
34 * based on the file, and returns zero otherwise.
38 check_rhosts_file(const char *filename, const char *hostname,
39 const char *ipaddr, const char *client_user,
40 const char *server_user)
43 char buf[1024]; /* Must not be larger than host, user, dummy below. */
45 /* Open the .rhosts file, deny if unreadable */
46 f = fopen(filename, "r");
50 while (fgets(buf, sizeof(buf), f)) {
51 /* All three must be at least as big as buf to avoid overflows. */
52 char hostbuf[1024], userbuf[1024], dummy[1024], *host, *user, *cp;
55 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
57 if (*cp == '#' || *cp == '\n' || !*cp)
61 * NO_PLUS is supported at least on OSF/1. We skip it (we
62 * don't ever support the plus syntax).
64 if (strncmp(cp, "NO_PLUS", 7) == 0)
68 * This should be safe because each buffer is as big as the
69 * whole string, and thus cannot be overwritten.
71 switch (sscanf(buf, "%s %s %s", hostbuf, userbuf, dummy)) {
73 packet_send_debug("Found empty line in %.100s.", filename);
77 strlcpy(userbuf, server_user, sizeof(userbuf));
80 /* Got both host and user name. */
83 packet_send_debug("Found garbage in %.100s.", filename);
94 /* Process negated host names, or positive netgroups. */
98 } else if (host[0] == '+')
101 if (user[0] == '-') {
104 } else if (user[0] == '+')
107 /* Check for empty host/user names (particularly '+'). */
108 if (!host[0] || !user[0]) {
109 /* We come here if either was '+' or '-'. */
110 packet_send_debug("Ignoring wild host/user names in %.100s.",
114 /* Verify that host name matches. */
115 if (host[0] == '@') {
116 if (!innetgr(host + 1, hostname, NULL, NULL) &&
117 !innetgr(host + 1, ipaddr, NULL, NULL))
119 } else if (strcasecmp(host, hostname) && strcmp(host, ipaddr) != 0)
120 continue; /* Different hostname. */
122 /* Verify that user name matches. */
123 if (user[0] == '@') {
124 if (!innetgr(user + 1, NULL, client_user, NULL))
126 } else if (strcmp(user, client_user) != 0)
127 continue; /* Different username. */
129 /* Found the user and host. */
132 /* If the entry was negated, deny access. */
134 packet_send_debug("Matched negative entry in %.100s.",
138 /* Accept authentication. */
142 /* Authentication using this file denied. */
148 * Tries to authenticate the user using the .shosts or .rhosts file. Returns
149 * true if authentication succeeds. If ignore_rhosts is true, only
150 * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
154 auth_rhosts(struct passwd *pw, const char *client_user)
156 const char *hostname, *ipaddr;
159 hostname = get_canonical_hostname(options.reverse_mapping_check);
160 ipaddr = get_remote_ipaddr();
161 ret = auth_rhosts2(pw, client_user, hostname, ipaddr);
166 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
171 static const char *rhosts_files[] = {".shosts", ".rhosts", NULL};
172 u_int rhosts_file_index;
174 debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s",
175 client_user, hostname, ipaddr);
181 /* Switch to the user's uid. */
182 temporarily_use_uid(pw);
184 * Quick check: if the user has no .shosts or .rhosts files, return
185 * failure immediately without doing costly lookups from name
188 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
189 rhosts_file_index++) {
190 /* Check users .rhosts or .shosts. */
191 snprintf(buf, sizeof buf, "%.500s/%.100s",
192 pw->pw_dir, rhosts_files[rhosts_file_index]);
193 if (stat(buf, &st) >= 0)
196 /* Switch back to privileged uid. */
199 /* Deny if The user has no .shosts or .rhosts file and there are no system-wide files. */
200 if (!rhosts_files[rhosts_file_index] &&
201 stat(_PATH_RHOSTS_EQUIV, &st) < 0 &&
202 stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0)
205 /* If not logging in as superuser, try /etc/hosts.equiv and shosts.equiv. */
206 if (pw->pw_uid != 0) {
207 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr, client_user,
209 packet_send_debug("Accepted for %.100s [%.100s] by /etc/hosts.equiv.",
213 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr, client_user,
215 packet_send_debug("Accepted for %.100s [%.100s] by %.100s.",
216 hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV);
221 * Check that the home directory is owned by root or the user, and is
222 * not group or world writable.
224 if (stat(pw->pw_dir, &st) < 0) {
225 log("Rhosts authentication refused for %.100s: no home directory %.200s",
226 pw->pw_name, pw->pw_dir);
227 packet_send_debug("Rhosts authentication refused for %.100s: no home directory %.200s",
228 pw->pw_name, pw->pw_dir);
231 if (options.strict_modes &&
232 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
233 (st.st_mode & 022) != 0)) {
234 log("Rhosts authentication refused for %.100s: bad ownership or modes for home directory.",
236 packet_send_debug("Rhosts authentication refused for %.100s: bad ownership or modes for home directory.",
240 /* Temporarily use the user's uid. */
241 temporarily_use_uid(pw);
243 /* Check all .rhosts files (currently .shosts and .rhosts). */
244 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
245 rhosts_file_index++) {
246 /* Check users .rhosts or .shosts. */
247 snprintf(buf, sizeof buf, "%.500s/%.100s",
248 pw->pw_dir, rhosts_files[rhosts_file_index]);
249 if (stat(buf, &st) < 0)
253 * Make sure that the file is either owned by the user or by
254 * root, and make sure it is not writable by anyone but the
255 * owner. This is to help avoid novices accidentally
256 * allowing access to their account by anyone.
258 if (options.strict_modes &&
259 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
260 (st.st_mode & 022) != 0)) {
261 log("Rhosts authentication refused for %.100s: bad modes for %.200s",
263 packet_send_debug("Bad file modes for %.200s", buf);
266 /* Check if we have been configured to ignore .rhosts and .shosts files. */
267 if (options.ignore_rhosts) {
268 packet_send_debug("Server has been configured to ignore %.100s.",
269 rhosts_files[rhosts_file_index]);
272 /* Check if authentication is permitted by the file. */
273 if (check_rhosts_file(buf, hostname, ipaddr, client_user, pw->pw_name)) {
274 packet_send_debug("Accepted by %.100s.",
275 rhosts_files[rhosts_file_index]);
276 /* Restore the privileged uid. */
282 /* Restore the privileged uid. */