5 * Author: Tatu Ylonen <ylo@cs.hut.fi>
7 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
10 * Created: Fri Mar 17 05:12:18 1995 ylo
12 * Rhosts authentication. This file contains code to check whether to admit
13 * the login based on rhosts authentication. This file also processes
28 * This function processes an rhosts-style file (.rhosts, .shosts, or
29 * /etc/hosts.equiv). This returns true if authentication can be granted
30 * based on the file, and returns zero otherwise.
34 check_rhosts_file(const char *filename, const char *hostname,
35 const char *ipaddr, const char *client_user,
36 const char *server_user)
39 char buf[1024]; /* Must not be larger than host, user, dummy below. */
41 /* Open the .rhosts file, deny if unreadable */
42 f = fopen(filename, "r");
46 while (fgets(buf, sizeof(buf), f)) {
47 /* All three must be at least as big as buf to avoid overflows. */
48 char hostbuf[1024], userbuf[1024], dummy[1024], *host, *user, *cp;
51 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
53 if (*cp == '#' || *cp == '\n' || !*cp)
57 * NO_PLUS is supported at least on OSF/1. We skip it (we
58 * don't ever support the plus syntax).
60 if (strncmp(cp, "NO_PLUS", 7) == 0)
64 * This should be safe because each buffer is as big as the
65 * whole string, and thus cannot be overwritten.
67 switch (sscanf(buf, "%s %s %s", hostbuf, userbuf, dummy)) {
69 packet_send_debug("Found empty line in %.100s.", filename);
73 strlcpy(userbuf, server_user, sizeof(userbuf));
76 /* Got both host and user name. */
79 packet_send_debug("Found garbage in %.100s.", filename);
90 /* Process negated host names, or positive netgroups. */
94 } else if (host[0] == '+')
100 } else if (user[0] == '+')
103 /* Check for empty host/user names (particularly '+'). */
104 if (!host[0] || !user[0]) {
105 /* We come here if either was '+' or '-'. */
106 packet_send_debug("Ignoring wild host/user names in %.100s.",
110 /* Verify that host name matches. */
111 if (host[0] == '@') {
112 if (!innetgr(host + 1, hostname, NULL, NULL) &&
113 !innetgr(host + 1, ipaddr, NULL, NULL))
115 } else if (strcasecmp(host, hostname) && strcmp(host, ipaddr) != 0)
116 continue; /* Different hostname. */
118 /* Verify that user name matches. */
119 if (user[0] == '@') {
120 if (!innetgr(user + 1, NULL, client_user, NULL))
122 } else if (strcmp(user, client_user) != 0)
123 continue; /* Different username. */
125 /* Found the user and host. */
128 /* If the entry was negated, deny access. */
130 packet_send_debug("Matched negative entry in %.100s.",
134 /* Accept authentication. */
138 /* Authentication using this file denied. */
144 * Tries to authenticate the user using the .shosts or .rhosts file. Returns
145 * true if authentication succeeds. If ignore_rhosts is true, only
146 * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
150 auth_rhosts(struct passwd *pw, const char *client_user)
152 extern ServerOptions options;
154 const char *hostname, *ipaddr;
156 static const char *rhosts_files[] = {".shosts", ".rhosts", NULL};
157 unsigned int rhosts_file_index;
159 /* Switch to the user's uid. */
160 temporarily_use_uid(pw->pw_uid);
162 * Quick check: if the user has no .shosts or .rhosts files, return
163 * failure immediately without doing costly lookups from name
166 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
167 rhosts_file_index++) {
168 /* Check users .rhosts or .shosts. */
169 snprintf(buf, sizeof buf, "%.500s/%.100s",
170 pw->pw_dir, rhosts_files[rhosts_file_index]);
171 if (stat(buf, &st) >= 0)
174 /* Switch back to privileged uid. */
177 /* Deny if The user has no .shosts or .rhosts file and there are no system-wide files. */
178 if (!rhosts_files[rhosts_file_index] &&
179 stat("/etc/hosts.equiv", &st) < 0 &&
180 stat(SSH_HOSTS_EQUIV, &st) < 0)
183 hostname = get_canonical_hostname();
184 ipaddr = get_remote_ipaddr();
186 /* If not logging in as superuser, try /etc/hosts.equiv and shosts.equiv. */
187 if (pw->pw_uid != 0) {
188 if (check_rhosts_file("/etc/hosts.equiv", hostname, ipaddr, client_user,
190 packet_send_debug("Accepted for %.100s [%.100s] by /etc/hosts.equiv.",
194 if (check_rhosts_file(SSH_HOSTS_EQUIV, hostname, ipaddr, client_user,
196 packet_send_debug("Accepted for %.100s [%.100s] by %.100s.",
197 hostname, ipaddr, SSH_HOSTS_EQUIV);
202 * Check that the home directory is owned by root or the user, and is
203 * not group or world writable.
205 if (stat(pw->pw_dir, &st) < 0) {
206 log("Rhosts authentication refused for %.100s: no home directory %.200s",
207 pw->pw_name, pw->pw_dir);
208 packet_send_debug("Rhosts authentication refused for %.100: no home directory %.200s",
209 pw->pw_name, pw->pw_dir);
212 if (options.strict_modes &&
213 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
214 (st.st_mode & 022) != 0)) {
215 log("Rhosts authentication refused for %.100s: bad ownership or modes for home directory.",
217 packet_send_debug("Rhosts authentication refused for %.100s: bad ownership or modes for home directory.",
221 /* Temporarily use the user's uid. */
222 temporarily_use_uid(pw->pw_uid);
224 /* Check all .rhosts files (currently .shosts and .rhosts). */
225 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
226 rhosts_file_index++) {
227 /* Check users .rhosts or .shosts. */
228 snprintf(buf, sizeof buf, "%.500s/%.100s",
229 pw->pw_dir, rhosts_files[rhosts_file_index]);
230 if (stat(buf, &st) < 0)
234 * Make sure that the file is either owned by the user or by
235 * root, and make sure it is not writable by anyone but the
236 * owner. This is to help avoid novices accidentally
237 * allowing access to their account by anyone.
239 if (options.strict_modes &&
240 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
241 (st.st_mode & 022) != 0)) {
242 log("Rhosts authentication refused for %.100s: bad modes for %.200s",
244 packet_send_debug("Bad file modes for %.200s", buf);
247 /* Check if we have been configured to ignore .rhosts and .shosts files. */
248 if (options.ignore_rhosts) {
249 packet_send_debug("Server has been configured to ignore %.100s.",
250 rhosts_files[rhosts_file_index]);
253 /* Check if authentication is permitted by the file. */
254 if (check_rhosts_file(buf, hostname, ipaddr, client_user, pw->pw_name)) {
255 packet_send_debug("Accepted by %.100s.",
256 rhosts_files[rhosts_file_index]);
257 /* Restore the privileged uid. */
263 /* Restore the privileged uid. */