1 /* $OpenBSD: auth-rhosts.c,v 1.38 2006/07/06 16:03:53 stevesk Exp $ */
3 * Author: Tatu Ylonen <ylo@cs.hut.fi>
4 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
6 * Rhosts authentication. This file contains code to check whether to admit
7 * the login based on rhosts authentication. This file also processes
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".
19 #include <sys/types.h>
22 #ifdef HAVE_NETGROUP_H
23 # include <netgroup.h>
29 #include "pathnames.h"
36 extern ServerOptions options;
37 extern int use_privsep;
40 * This function processes an rhosts-style file (.rhosts, .shosts, or
41 * /etc/hosts.equiv). This returns true if authentication can be granted
42 * based on the file, and returns zero otherwise.
46 check_rhosts_file(const char *filename, const char *hostname,
47 const char *ipaddr, const char *client_user,
48 const char *server_user)
51 char buf[1024]; /* Must not be larger than host, user, dummy below. */
53 /* Open the .rhosts file, deny if unreadable */
54 f = fopen(filename, "r");
58 while (fgets(buf, sizeof(buf), f)) {
59 /* All three must be at least as big as buf to avoid overflows. */
60 char hostbuf[1024], userbuf[1024], dummy[1024], *host, *user, *cp;
63 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
65 if (*cp == '#' || *cp == '\n' || !*cp)
69 * NO_PLUS is supported at least on OSF/1. We skip it (we
70 * don't ever support the plus syntax).
72 if (strncmp(cp, "NO_PLUS", 7) == 0)
76 * This should be safe because each buffer is as big as the
77 * whole string, and thus cannot be overwritten.
79 switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf,
82 auth_debug_add("Found empty line in %.100s.", filename);
86 strlcpy(userbuf, server_user, sizeof(userbuf));
89 /* Got both host and user name. */
92 auth_debug_add("Found garbage in %.100s.", filename);
103 /* Process negated host names, or positive netgroups. */
104 if (host[0] == '-') {
107 } else if (host[0] == '+')
110 if (user[0] == '-') {
113 } else if (user[0] == '+')
116 /* Check for empty host/user names (particularly '+'). */
117 if (!host[0] || !user[0]) {
118 /* We come here if either was '+' or '-'. */
119 auth_debug_add("Ignoring wild host/user names in %.100s.",
123 /* Verify that host name matches. */
124 if (host[0] == '@') {
125 if (!innetgr(host + 1, hostname, NULL, NULL) &&
126 !innetgr(host + 1, ipaddr, NULL, NULL))
128 } else if (strcasecmp(host, hostname) && strcmp(host, ipaddr) != 0)
129 continue; /* Different hostname. */
131 /* Verify that user name matches. */
132 if (user[0] == '@') {
133 if (!innetgr(user + 1, NULL, client_user, NULL))
135 } else if (strcmp(user, client_user) != 0)
136 continue; /* Different username. */
138 /* Found the user and host. */
141 /* If the entry was negated, deny access. */
143 auth_debug_add("Matched negative entry in %.100s.",
147 /* Accept authentication. */
151 /* Authentication using this file denied. */
157 * Tries to authenticate the user using the .shosts or .rhosts file. Returns
158 * true if authentication succeeds. If ignore_rhosts is true, only
159 * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
163 auth_rhosts(struct passwd *pw, const char *client_user)
165 const char *hostname, *ipaddr;
167 hostname = get_canonical_hostname(options.use_dns);
168 ipaddr = get_remote_ipaddr();
169 return auth_rhosts2(pw, client_user, hostname, ipaddr);
173 auth_rhosts2_raw(struct passwd *pw, const char *client_user, const char *hostname,
178 static const char *rhosts_files[] = {".shosts", ".rhosts", NULL};
179 u_int rhosts_file_index;
181 debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s",
182 client_user, hostname, ipaddr);
184 /* Switch to the user's uid. */
185 temporarily_use_uid(pw);
187 * Quick check: if the user has no .shosts or .rhosts files, return
188 * failure immediately without doing costly lookups from name
191 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
192 rhosts_file_index++) {
193 /* Check users .rhosts or .shosts. */
194 snprintf(buf, sizeof buf, "%.500s/%.100s",
195 pw->pw_dir, rhosts_files[rhosts_file_index]);
196 if (stat(buf, &st) >= 0)
199 /* Switch back to privileged uid. */
202 /* Deny if The user has no .shosts or .rhosts file and there are no system-wide files. */
203 if (!rhosts_files[rhosts_file_index] &&
204 stat(_PATH_RHOSTS_EQUIV, &st) < 0 &&
205 stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0)
208 /* If not logging in as superuser, try /etc/hosts.equiv and shosts.equiv. */
209 if (pw->pw_uid != 0) {
210 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr,
211 client_user, pw->pw_name)) {
212 auth_debug_add("Accepted for %.100s [%.100s] by /etc/hosts.equiv.",
216 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr,
217 client_user, pw->pw_name)) {
218 auth_debug_add("Accepted for %.100s [%.100s] by %.100s.",
219 hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV);
224 * Check that the home directory is owned by root or the user, and is
225 * not group or world writable.
227 if (stat(pw->pw_dir, &st) < 0) {
228 logit("Rhosts authentication refused for %.100s: "
229 "no home directory %.200s", pw->pw_name, pw->pw_dir);
230 auth_debug_add("Rhosts authentication refused for %.100s: "
231 "no home directory %.200s", pw->pw_name, pw->pw_dir);
234 if (options.strict_modes &&
235 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
236 (st.st_mode & 022) != 0)) {
237 logit("Rhosts authentication refused for %.100s: "
238 "bad ownership or modes for home directory.", pw->pw_name);
239 auth_debug_add("Rhosts authentication refused for %.100s: "
240 "bad ownership or modes for home directory.", pw->pw_name);
243 /* Temporarily use the user's uid. */
244 temporarily_use_uid(pw);
246 /* Check all .rhosts files (currently .shosts and .rhosts). */
247 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
248 rhosts_file_index++) {
249 /* Check users .rhosts or .shosts. */
250 snprintf(buf, sizeof buf, "%.500s/%.100s",
251 pw->pw_dir, rhosts_files[rhosts_file_index]);
252 if (stat(buf, &st) < 0)
256 * Make sure that the file is either owned by the user or by
257 * root, and make sure it is not writable by anyone but the
258 * owner. This is to help avoid novices accidentally
259 * allowing access to their account by anyone.
261 if (options.strict_modes &&
262 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
263 (st.st_mode & 022) != 0)) {
264 logit("Rhosts authentication refused for %.100s: bad modes for %.200s",
266 auth_debug_add("Bad file modes for %.200s", buf);
269 /* Check if we have been configured to ignore .rhosts and .shosts files. */
270 if (options.ignore_rhosts) {
271 auth_debug_add("Server has been configured to ignore %.100s.",
272 rhosts_files[rhosts_file_index]);
275 /* Check if authentication is permitted by the file. */
276 if (check_rhosts_file(buf, hostname, ipaddr, client_user, pw->pw_name)) {
277 auth_debug_add("Accepted by %.100s.",
278 rhosts_files[rhosts_file_index]);
279 /* Restore the privileged uid. */
281 auth_debug_add("Accepted host %s ip %s client_user %s server_user %s",
282 hostname, ipaddr, client_user, pw->pw_name);
287 /* Restore the privileged uid. */
293 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
299 ret = auth_rhosts2_raw(pw, client_user, hostname, ipaddr);