1 /* $OpenBSD: auth-rhosts.c,v 1.44 2010/03/07 11:57:13 dtucker Exp $ */
2 /*
3 * Author: Tatu Ylonen <ylo@cs.hut.fi>
4 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5 * All rights reserved
6 * Rhosts authentication. This file contains code to check whether to admit
7 * the login based on rhosts authentication. This file also processes
8 * /etc/hosts.equiv.
9 *
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".
15 */
16
17 #include "includes.h"
18
19 #include <sys/types.h>
20 #include <sys/stat.h>
21
22 #ifdef HAVE_NETGROUP_H
23 # include <netgroup.h>
24 #endif
25 #include <pwd.h>
26 #include <stdio.h>
27 #include <string.h>
28 #include <stdarg.h>
29 #include <fcntl.h>
30 #include <unistd.h>
31
32 #include "packet.h"
33 #include "buffer.h"
34 #include "uidswap.h"
35 #include "pathnames.h"
36 #include "log.h"
37 #include "servconf.h"
38 #include "canohost.h"
39 #include "key.h"
40 #include "hostfile.h"
41 #include "auth.h"
42 #include "misc.h"
43
44 /* import */
45 extern ServerOptions options;
46 extern int use_privsep;
47
48 /*
49 * This function processes an rhosts-style file (.rhosts, .shosts, or
50 * /etc/hosts.equiv). This returns true if authentication can be granted
51 * based on the file, and returns zero otherwise.
52 */
53
54 static int
check_rhosts_file(const char * filename,const char * hostname,const char * ipaddr,const char * client_user,const char * server_user)55 check_rhosts_file(const char *filename, const char *hostname,
56 const char *ipaddr, const char *client_user,
57 const char *server_user)
58 {
59 FILE *f;
60 char buf[1024]; /* Must not be larger than host, user, dummy below. */
61 int fd;
62 struct stat st;
63
64 /* Open the .rhosts file, deny if unreadable */
65 if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1)
66 return 0;
67 if (fstat(fd, &st) == -1) {
68 close(fd);
69 return 0;
70 }
71 if (!S_ISREG(st.st_mode)) {
72 logit("User %s hosts file %s is not a regular file",
73 server_user, filename);
74 close(fd);
75 return 0;
76 }
77 unset_nonblock(fd);
78 if ((f = fdopen(fd, "r")) == NULL) {
79 close(fd);
80 return 0;
81 }
82 while (fgets(buf, sizeof(buf), f)) {
83 /* All three must be at least as big as buf to avoid overflows. */
84 char hostbuf[1024], userbuf[1024], dummy[1024], *host, *user, *cp;
85 int negated;
86
87 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
88 ;
89 if (*cp == '#' || *cp == '\n' || !*cp)
90 continue;
91
92 /*
93 * NO_PLUS is supported at least on OSF/1. We skip it (we
94 * don't ever support the plus syntax).
95 */
96 if (strncmp(cp, "NO_PLUS", 7) == 0)
97 continue;
98
99 /*
100 * This should be safe because each buffer is as big as the
101 * whole string, and thus cannot be overwritten.
102 */
103 switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf,
104 dummy)) {
105 case 0:
106 auth_debug_add("Found empty line in %.100s.", filename);
107 continue;
108 case 1:
109 /* Host name only. */
110 strlcpy(userbuf, server_user, sizeof(userbuf));
111 break;
112 case 2:
113 /* Got both host and user name. */
114 break;
115 case 3:
116 auth_debug_add("Found garbage in %.100s.", filename);
117 continue;
118 default:
119 /* Weird... */
120 continue;
121 }
122
123 host = hostbuf;
124 user = userbuf;
125 negated = 0;
126
127 /* Process negated host names, or positive netgroups. */
128 if (host[0] == '-') {
129 negated = 1;
130 host++;
131 } else if (host[0] == '+')
132 host++;
133
134 if (user[0] == '-') {
135 negated = 1;
136 user++;
137 } else if (user[0] == '+')
138 user++;
139
140 /* Check for empty host/user names (particularly '+'). */
141 if (!host[0] || !user[0]) {
142 /* We come here if either was '+' or '-'. */
143 auth_debug_add("Ignoring wild host/user names in %.100s.",
144 filename);
145 continue;
146 }
147 /* Verify that host name matches. */
148 if (host[0] == '@') {
149 if (!innetgr(host + 1, hostname, NULL, NULL) &&
150 !innetgr(host + 1, ipaddr, NULL, NULL))
151 continue;
152 } else if (strcasecmp(host, hostname) && strcmp(host, ipaddr) != 0)
153 continue; /* Different hostname. */
154
155 /* Verify that user name matches. */
156 if (user[0] == '@') {
157 if (!innetgr(user + 1, NULL, client_user, NULL))
158 continue;
159 } else if (strcmp(user, client_user) != 0)
160 continue; /* Different username. */
161
162 /* Found the user and host. */
163 fclose(f);
164
165 /* If the entry was negated, deny access. */
166 if (negated) {
167 auth_debug_add("Matched negative entry in %.100s.",
168 filename);
169 return 0;
170 }
171 /* Accept authentication. */
172 return 1;
173 }
174
175 /* Authentication using this file denied. */
176 fclose(f);
177 return 0;
178 }
179
180 /*
181 * Tries to authenticate the user using the .shosts or .rhosts file. Returns
182 * true if authentication succeeds. If ignore_rhosts is true, only
183 * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
184 */
185
186 int
auth_rhosts(struct passwd * pw,const char * client_user)187 auth_rhosts(struct passwd *pw, const char *client_user)
188 {
189 const char *hostname, *ipaddr;
190
191 hostname = get_canonical_hostname(options.use_dns);
192 ipaddr = get_remote_ipaddr();
193 return auth_rhosts2(pw, client_user, hostname, ipaddr);
194 }
195
196 static int
auth_rhosts2_raw(struct passwd * pw,const char * client_user,const char * hostname,const char * ipaddr)197 auth_rhosts2_raw(struct passwd *pw, const char *client_user, const char *hostname,
198 const char *ipaddr)
199 {
200 char buf[1024];
201 struct stat st;
202 static const char *rhosts_files[] = {".shosts", ".rhosts", NULL};
203 u_int rhosts_file_index;
204
205 debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s",
206 client_user, hostname, ipaddr);
207
208 /* Switch to the user's uid. */
209 temporarily_use_uid(pw);
210 /*
211 * Quick check: if the user has no .shosts or .rhosts files, return
212 * failure immediately without doing costly lookups from name
213 * servers.
214 */
215 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
216 rhosts_file_index++) {
217 /* Check users .rhosts or .shosts. */
218 snprintf(buf, sizeof buf, "%.500s/%.100s",
219 pw->pw_dir, rhosts_files[rhosts_file_index]);
220 if (stat(buf, &st) >= 0)
221 break;
222 }
223 /* Switch back to privileged uid. */
224 restore_uid();
225
226 /* Deny if The user has no .shosts or .rhosts file and there are no system-wide files. */
227 if (!rhosts_files[rhosts_file_index] &&
228 stat(_PATH_RHOSTS_EQUIV, &st) < 0 &&
229 stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0)
230 return 0;
231
232 /* If not logging in as superuser, try /etc/hosts.equiv and shosts.equiv. */
233 if (pw->pw_uid != 0) {
234 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr,
235 client_user, pw->pw_name)) {
236 auth_debug_add("Accepted for %.100s [%.100s] by /etc/hosts.equiv.",
237 hostname, ipaddr);
238 return 1;
239 }
240 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr,
241 client_user, pw->pw_name)) {
242 auth_debug_add("Accepted for %.100s [%.100s] by %.100s.",
243 hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV);
244 return 1;
245 }
246 }
247 /*
248 * Check that the home directory is owned by root or the user, and is
249 * not group or world writable.
250 */
251 if (stat(pw->pw_dir, &st) < 0) {
252 logit("Rhosts authentication refused for %.100s: "
253 "no home directory %.200s", pw->pw_name, pw->pw_dir);
254 auth_debug_add("Rhosts authentication refused for %.100s: "
255 "no home directory %.200s", pw->pw_name, pw->pw_dir);
256 return 0;
257 }
258 if (options.strict_modes &&
259 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
260 (st.st_mode & 022) != 0)) {
261 logit("Rhosts authentication refused for %.100s: "
262 "bad ownership or modes for home directory.", pw->pw_name);
263 auth_debug_add("Rhosts authentication refused for %.100s: "
264 "bad ownership or modes for home directory.", pw->pw_name);
265 return 0;
266 }
267 /* Temporarily use the user's uid. */
268 temporarily_use_uid(pw);
269
270 /* Check all .rhosts files (currently .shosts and .rhosts). */
271 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
272 rhosts_file_index++) {
273 /* Check users .rhosts or .shosts. */
274 snprintf(buf, sizeof buf, "%.500s/%.100s",
275 pw->pw_dir, rhosts_files[rhosts_file_index]);
276 if (stat(buf, &st) < 0)
277 continue;
278
279 /*
280 * Make sure that the file is either owned by the user or by
281 * root, and make sure it is not writable by anyone but the
282 * owner. This is to help avoid novices accidentally
283 * allowing access to their account by anyone.
284 */
285 if (options.strict_modes &&
286 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
287 (st.st_mode & 022) != 0)) {
288 logit("Rhosts authentication refused for %.100s: bad modes for %.200s",
289 pw->pw_name, buf);
290 auth_debug_add("Bad file modes for %.200s", buf);
291 continue;
292 }
293 /* Check if we have been configured to ignore .rhosts and .shosts files. */
294 if (options.ignore_rhosts) {
295 auth_debug_add("Server has been configured to ignore %.100s.",
296 rhosts_files[rhosts_file_index]);
297 continue;
298 }
299 /* Check if authentication is permitted by the file. */
300 if (check_rhosts_file(buf, hostname, ipaddr, client_user, pw->pw_name)) {
301 auth_debug_add("Accepted by %.100s.",
302 rhosts_files[rhosts_file_index]);
303 /* Restore the privileged uid. */
304 restore_uid();
305 auth_debug_add("Accepted host %s ip %s client_user %s server_user %s",
306 hostname, ipaddr, client_user, pw->pw_name);
307 return 1;
308 }
309 }
310
311 /* Restore the privileged uid. */
312 restore_uid();
313 return 0;
314 }
315
316 int
auth_rhosts2(struct passwd * pw,const char * client_user,const char * hostname,const char * ipaddr)317 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
318 const char *ipaddr)
319 {
320 return auth_rhosts2_raw(pw, client_user, hostname, ipaddr);
321 }
322