1 /* $OpenBSD: auth-rhosts.c,v 1.40 2006/08/01 23:22:47 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>
31 #include "pathnames.h"
38 extern ServerOptions options;
39 extern int use_privsep;
42 * This function processes an rhosts-style file (.rhosts, .shosts, or
43 * /etc/hosts.equiv). This returns true if authentication can be granted
44 * based on the file, and returns zero otherwise.
48 check_rhosts_file(const char *filename, const char *hostname,
49 const char *ipaddr, const char *client_user,
50 const char *server_user)
53 char buf[1024]; /* Must not be larger than host, user, dummy below. */
55 /* Open the .rhosts file, deny if unreadable */
56 f = fopen(filename, "r");
60 while (fgets(buf, sizeof(buf), f)) {
61 /* All three must be at least as big as buf to avoid overflows. */
62 char hostbuf[1024], userbuf[1024], dummy[1024], *host, *user, *cp;
65 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
67 if (*cp == '#' || *cp == '\n' || !*cp)
71 * NO_PLUS is supported at least on OSF/1. We skip it (we
72 * don't ever support the plus syntax).
74 if (strncmp(cp, "NO_PLUS", 7) == 0)
78 * This should be safe because each buffer is as big as the
79 * whole string, and thus cannot be overwritten.
81 switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf,
84 auth_debug_add("Found empty line in %.100s.", filename);
88 strlcpy(userbuf, server_user, sizeof(userbuf));
91 /* Got both host and user name. */
94 auth_debug_add("Found garbage in %.100s.", filename);
105 /* Process negated host names, or positive netgroups. */
106 if (host[0] == '-') {
109 } else if (host[0] == '+')
112 if (user[0] == '-') {
115 } else if (user[0] == '+')
118 /* Check for empty host/user names (particularly '+'). */
119 if (!host[0] || !user[0]) {
120 /* We come here if either was '+' or '-'. */
121 auth_debug_add("Ignoring wild host/user names in %.100s.",
125 /* Verify that host name matches. */
126 if (host[0] == '@') {
127 if (!innetgr(host + 1, hostname, NULL, NULL) &&
128 !innetgr(host + 1, ipaddr, NULL, NULL))
130 } else if (strcasecmp(host, hostname) && strcmp(host, ipaddr) != 0)
131 continue; /* Different hostname. */
133 /* Verify that user name matches. */
134 if (user[0] == '@') {
135 if (!innetgr(user + 1, NULL, client_user, NULL))
137 } else if (strcmp(user, client_user) != 0)
138 continue; /* Different username. */
140 /* Found the user and host. */
143 /* If the entry was negated, deny access. */
145 auth_debug_add("Matched negative entry in %.100s.",
149 /* Accept authentication. */
153 /* Authentication using this file denied. */
159 * Tries to authenticate the user using the .shosts or .rhosts file. Returns
160 * true if authentication succeeds. If ignore_rhosts is true, only
161 * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
165 auth_rhosts(struct passwd *pw, const char *client_user)
167 const char *hostname, *ipaddr;
169 hostname = get_canonical_hostname(options.use_dns);
170 ipaddr = get_remote_ipaddr();
171 return auth_rhosts2(pw, client_user, hostname, ipaddr);
175 auth_rhosts2_raw(struct passwd *pw, const char *client_user, const char *hostname,
180 static const char *rhosts_files[] = {".shosts", ".rhosts", NULL};
181 u_int rhosts_file_index;
183 debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s",
184 client_user, hostname, ipaddr);
186 /* Switch to the user's uid. */
187 temporarily_use_uid(pw);
189 * Quick check: if the user has no .shosts or .rhosts files, return
190 * failure immediately without doing costly lookups from name
193 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
194 rhosts_file_index++) {
195 /* Check users .rhosts or .shosts. */
196 snprintf(buf, sizeof buf, "%.500s/%.100s",
197 pw->pw_dir, rhosts_files[rhosts_file_index]);
198 if (stat(buf, &st) >= 0)
201 /* Switch back to privileged uid. */
204 /* Deny if The user has no .shosts or .rhosts file and there are no system-wide files. */
205 if (!rhosts_files[rhosts_file_index] &&
206 stat(_PATH_RHOSTS_EQUIV, &st) < 0 &&
207 stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0)
210 /* If not logging in as superuser, try /etc/hosts.equiv and shosts.equiv. */
211 if (pw->pw_uid != 0) {
212 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr,
213 client_user, pw->pw_name)) {
214 auth_debug_add("Accepted for %.100s [%.100s] by /etc/hosts.equiv.",
218 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr,
219 client_user, pw->pw_name)) {
220 auth_debug_add("Accepted for %.100s [%.100s] by %.100s.",
221 hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV);
226 * Check that the home directory is owned by root or the user, and is
227 * not group or world writable.
229 if (stat(pw->pw_dir, &st) < 0) {
230 logit("Rhosts authentication refused for %.100s: "
231 "no home directory %.200s", pw->pw_name, pw->pw_dir);
232 auth_debug_add("Rhosts authentication refused for %.100s: "
233 "no home directory %.200s", pw->pw_name, pw->pw_dir);
236 if (options.strict_modes &&
237 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
238 (st.st_mode & 022) != 0)) {
239 logit("Rhosts authentication refused for %.100s: "
240 "bad ownership or modes for home directory.", pw->pw_name);
241 auth_debug_add("Rhosts authentication refused for %.100s: "
242 "bad ownership or modes for home directory.", pw->pw_name);
245 /* Temporarily use the user's uid. */
246 temporarily_use_uid(pw);
248 /* Check all .rhosts files (currently .shosts and .rhosts). */
249 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
250 rhosts_file_index++) {
251 /* Check users .rhosts or .shosts. */
252 snprintf(buf, sizeof buf, "%.500s/%.100s",
253 pw->pw_dir, rhosts_files[rhosts_file_index]);
254 if (stat(buf, &st) < 0)
258 * Make sure that the file is either owned by the user or by
259 * root, and make sure it is not writable by anyone but the
260 * owner. This is to help avoid novices accidentally
261 * allowing access to their account by anyone.
263 if (options.strict_modes &&
264 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
265 (st.st_mode & 022) != 0)) {
266 logit("Rhosts authentication refused for %.100s: bad modes for %.200s",
268 auth_debug_add("Bad file modes for %.200s", buf);
271 /* Check if we have been configured to ignore .rhosts and .shosts files. */
272 if (options.ignore_rhosts) {
273 auth_debug_add("Server has been configured to ignore %.100s.",
274 rhosts_files[rhosts_file_index]);
277 /* Check if authentication is permitted by the file. */
278 if (check_rhosts_file(buf, hostname, ipaddr, client_user, pw->pw_name)) {
279 auth_debug_add("Accepted by %.100s.",
280 rhosts_files[rhosts_file_index]);
281 /* Restore the privileged uid. */
283 auth_debug_add("Accepted host %s ip %s client_user %s server_user %s",
284 hostname, ipaddr, client_user, pw->pw_name);
289 /* Restore the privileged uid. */
295 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
301 ret = auth_rhosts2_raw(pw, client_user, hostname, ipaddr);