1 /* $OpenBSD: auth-rhosts.c,v 1.56 2022/02/23 21:21:49 djm 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>
23 #ifdef HAVE_NETGROUP_H
24 # include <netgroup.h>
35 #include "pathnames.h"
47 extern ServerOptions options;
48 extern int use_privsep;
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.
57 check_rhosts_file(const char *filename, const char *hostname,
58 const char *ipaddr, const char *client_user,
59 const char *server_user)
63 char buf[RBUFLN];/* Must not be larger than host, user, dummy below. */
67 /* Open the .rhosts file, deny if unreadable */
68 if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1)
70 if (fstat(fd, &st) == -1) {
74 if (!S_ISREG(st.st_mode)) {
75 logit("User %s hosts file %s is not a regular file",
76 server_user, filename);
81 if ((f = fdopen(fd, "r")) == NULL) {
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;
91 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
93 if (*cp == '#' || *cp == '\n' || !*cp)
97 * NO_PLUS is supported at least on OSF/1. We skip it (we
98 * don't ever support the plus syntax).
100 if (strncmp(cp, "NO_PLUS", 7) == 0)
104 * This should be safe because each buffer is as big as the
105 * whole string, and thus cannot be overwritten.
107 switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf,
110 auth_debug_add("Found empty line in %.100s.", filename);
113 /* Host name only. */
114 strlcpy(userbuf, server_user, sizeof(userbuf));
117 /* Got both host and user name. */
120 auth_debug_add("Found garbage in %.100s.", filename);
131 /* Process negated host names, or positive netgroups. */
132 if (host[0] == '-') {
135 } else if (host[0] == '+')
138 if (user[0] == '-') {
141 } else if (user[0] == '+')
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);
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))
156 } else if (strcasecmp(host, hostname) &&
157 strcmp(host, ipaddr) != 0)
158 continue; /* Different hostname. */
160 /* Verify that user name matches. */
161 if (user[0] == '@') {
162 if (!innetgr(user + 1, NULL, client_user, NULL))
164 } else if (strcmp(user, client_user) != 0)
165 continue; /* Different username. */
167 /* Found the user and host. */
170 /* If the entry was negated, deny access. */
172 auth_debug_add("Matched negative entry in %.100s.",
176 /* Accept authentication. */
180 /* Authentication using this file denied. */
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).
191 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
196 static const char * const rhosts_files[] = {".shosts", ".rhosts", NULL};
197 u_int rhosts_file_index;
200 debug2_f("clientuser %s hostname %s ipaddr %s",
201 client_user, hostname, ipaddr);
203 /* Switch to the user's uid. */
204 temporarily_use_uid(pw);
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
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]);
221 /* Switch back to privileged uid. */
225 * Deny if The user has no .shosts or .rhosts file and there
226 * are no system-wide files.
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");
236 * If not logging in as superuser, try /etc/hosts.equiv and
240 debug3_f("root user, ignoring system hosts files");
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);
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);
257 * Check that the home directory is owned by root or the user, and is
258 * not group or world writable.
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);
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);
276 /* Temporarily use the user's uid. */
277 temporarily_use_uid(pw);
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) {
291 * Make sure that the file is either owned by the user or by
292 * root, and make sure it is not writable by anyone but the
293 * owner. This is to help avoid novices accidentally
294 * allowing access to their account by anyone.
296 if (options.strict_modes &&
297 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
298 (st.st_mode & 022) != 0)) {
299 logit("Rhosts authentication refused for %.100s: "
300 "bad modes for %.200s", pw->pw_name, path);
301 auth_debug_add("Bad file modes for %.200s", path);
306 * Check if we have been configured to ignore .rhosts
309 if (options.ignore_rhosts == IGNORE_RHOSTS_YES ||
310 (options.ignore_rhosts == IGNORE_RHOSTS_SHOSTS &&
311 strcmp(rhosts_files[rhosts_file_index], ".shosts") != 0)) {
312 auth_debug_add("Server has been configured to "
313 "ignore %.100s.", rhosts_files[rhosts_file_index]);
317 /* Check if authentication is permitted by the file. */
318 if (check_rhosts_file(path, hostname, ipaddr,
319 client_user, pw->pw_name)) {
320 auth_debug_add("Accepted by %.100s.",
321 rhosts_files[rhosts_file_index]);
322 /* Restore the privileged uid. */
324 auth_debug_add("Accepted host %s ip %s client_user "
325 "%s server_user %s", hostname, ipaddr,
326 client_user, pw->pw_name);
333 /* Restore the privileged uid. */