1 /*
2 * Author: Tatu Ylonen <ylo@cs.hut.fi>
3 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4 * All rights reserved
5 * Rhosts authentication. This file contains code to check whether to admit
6 * the login based on rhosts authentication. This file also processes
7 * /etc/hosts.equiv.
8 *
9 * As far as I am concerned, the code I have written for this software
10 * can be used freely for any purpose. Any derived versions of this
11 * software must be clearly marked as such, and if the derived work is
12 * incompatible with the protocol description in the RFC file, it must be
13 * called by a name other than "ssh" or "Secure Shell".
14 */
15
16 #include "includes.h"
17 RCSID("$OpenBSD: auth-rhosts.c,v 1.28 2002/05/13 21:26:49 markus Exp $");
18
19 #pragma ident "%Z%%M% %I% %E% SMI"
20
21 #include "packet.h"
22 #include "uidswap.h"
23 #include "pathnames.h"
24 #include "log.h"
25 #include "servconf.h"
26 #include "canohost.h"
27 #include "auth.h"
28
29 /* import */
30 extern ServerOptions options;
31
32 /*
33 * This function processes an rhosts-style file (.rhosts, .shosts, or
34 * /etc/hosts.equiv). This returns true if authentication can be granted
35 * based on the file, and returns zero otherwise.
36 */
37
38 static int
39 check_rhosts_file(const char *filename, const char *hostname,
40 const char *ipaddr, const char *client_user,
41 const char *server_user)
42 {
43 FILE *f;
44 char buf[1024]; /* Must not be larger than host, user, dummy below. */
45
46 /* Open the .rhosts file, deny if unreadable */
47 f = fopen(filename, "r");
48 if (!f)
49 return 0;
50
51 while (fgets(buf, sizeof(buf), f)) {
52 /* All three must be at least as big as buf to avoid overflows. */
53 char hostbuf[1024], userbuf[1024], dummy[1024], *host, *user, *cp;
54 int negated;
55
56 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
57 ;
58 if (*cp == '#' || *cp == '\n' || !*cp)
59 continue;
60
61 /*
62 * NO_PLUS is supported at least on OSF/1. We skip it (we
63 * don't ever support the plus syntax).
64 */
65 if (strncmp(cp, "NO_PLUS", 7) == 0)
66 continue;
67
68 /*
69 * This should be safe because each buffer is as big as the
70 * whole string, and thus cannot be overwritten.
71 */
72 switch (sscanf(buf, "%1024s %1024s %1024s",
73 hostbuf, userbuf, dummy)) {
74 case 0:
75 auth_debug_add("Found empty line in %.100s.", filename);
76 continue;
77 case 1:
78 /* Host name only. */
79 strlcpy(userbuf, server_user, sizeof(userbuf));
80 break;
81 case 2:
82 /* Got both host and user name. */
83 break;
84 case 3:
85 auth_debug_add("Found garbage in %.100s.", filename);
86 continue;
87 default:
88 /* Weird... */
89 continue;
90 }
91
92 host = hostbuf;
93 user = userbuf;
94 negated = 0;
95
96 /* Process negated host names, or positive netgroups. */
97 if (host[0] == '-') {
98 negated = 1;
99 host++;
100 } else if (host[0] == '+')
101 host++;
102
103 if (user[0] == '-') {
104 negated = 1;
105 user++;
106 } else if (user[0] == '+')
107 user++;
108
109 /* Check for empty host/user names (particularly '+'). */
110 if (!host[0] || !user[0]) {
111 /* We come here if either was '+' or '-'. */
112 auth_debug_add("Ignoring wild host/user names in %.100s.",
113 filename);
114 continue;
115 }
116 /* Verify that host name matches. */
117 if (host[0] == '@') {
118 if (!innetgr(host + 1, hostname, NULL, NULL) &&
119 !innetgr(host + 1, ipaddr, NULL, NULL))
120 continue;
121 } else if (strcasecmp(host, hostname) && strcmp(host, ipaddr) != 0)
122 continue; /* Different hostname. */
123
124 /* Verify that user name matches. */
125 if (user[0] == '@') {
126 if (!innetgr(user + 1, NULL, client_user, NULL))
127 continue;
128 } else if (strcmp(user, client_user) != 0)
129 continue; /* Different username. */
130
131 /* Found the user and host. */
132 fclose(f);
133
134 /* If the entry was negated, deny access. */
135 if (negated) {
136 auth_debug_add("Matched negative entry in %.100s.",
137 filename);
138 return 0;
139 }
140 /* Accept authentication. */
141 return 1;
142 }
143
144 /* Authentication using this file denied. */
145 fclose(f);
146 return 0;
147 }
148
149 /*
150 * Tries to authenticate the user using the .shosts or .rhosts file. Returns
151 * true if authentication succeeds. If ignore_rhosts is true, only
152 * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
153 */
154
155 int
156 auth_rhosts(struct passwd *pw, const char *client_user)
157 {
158 const char *hostname, *ipaddr;
159
160 hostname = get_canonical_hostname(options.verify_reverse_mapping);
161 ipaddr = get_remote_ipaddr();
162 return auth_rhosts2(pw, client_user, hostname, ipaddr);
163 }
164
165 static int
166 auth_rhosts2_raw(struct passwd *pw, const char *client_user, const char *hostname,
167 const char *ipaddr)
168 {
169 char buf[1024];
170 struct stat st;
171 static const char *rhosts_files[] = {".shosts", ".rhosts", NULL};
172 u_int rhosts_file_index;
173
174 debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s",
175 client_user, hostname, ipaddr);
176
177 /* no user given */
178 if (pw == NULL)
179 return 0;
180
181 /* Switch to the user's uid. */
182 temporarily_use_uid(pw);
183 /*
184 * Quick check: if the user has no .shosts or .rhosts files, return
185 * failure immediately without doing costly lookups from name
186 * servers.
187 */
188 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
189 rhosts_file_index++) {
190 /* Check users .rhosts or .shosts. */
191 snprintf(buf, sizeof buf, "%.500s/%.100s",
192 pw->pw_dir, rhosts_files[rhosts_file_index]);
193 if (stat(buf, &st) >= 0)
194 break;
195 }
196 /* Switch back to privileged uid. */
197 restore_uid();
198
199 /* Deny if The user has no .shosts or .rhosts file and there are no system-wide files. */
200 if (!rhosts_files[rhosts_file_index] &&
201 stat(_PATH_RHOSTS_EQUIV, &st) < 0 &&
202 stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0)
203 return 0;
204
205 /* If not logging in as superuser, try /etc/hosts.equiv and shosts.equiv. */
206 if (pw->pw_uid != 0) {
207 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr,
208 client_user, pw->pw_name)) {
209 auth_debug_add("Accepted for %.100s [%.100s] by /etc/hosts.equiv.",
210 hostname, ipaddr);
211 return 1;
212 }
213 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr,
214 client_user, pw->pw_name)) {
215 auth_debug_add("Accepted for %.100s [%.100s] by %.100s.",
216 hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV);
217 return 1;
218 }
219 }
220 /*
221 * Check that the home directory is owned by root or the user, and is
222 * not group or world writable.
223 */
224 if (stat(pw->pw_dir, &st) < 0) {
225 log("Rhosts authentication refused for %.100s: "
226 "no home directory %.200s", pw->pw_name, pw->pw_dir);
227 auth_debug_add("Rhosts authentication refused for %.100s: "
228 "no home directory %.200s", pw->pw_name, pw->pw_dir);
229 return 0;
230 }
231 if (options.strict_modes &&
232 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
233 (st.st_mode & 022) != 0)) {
234 log("Rhosts authentication refused for %.100s: "
235 "bad ownership or modes for home directory.", pw->pw_name);
236 auth_debug_add("Rhosts authentication refused for %.100s: "
237 "bad ownership or modes for home directory.", pw->pw_name);
238 return 0;
239 }
240 /* Temporarily use the user's uid. */
241 temporarily_use_uid(pw);
242
243 /* Check all .rhosts files (currently .shosts and .rhosts). */
244 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
245 rhosts_file_index++) {
246 /* Check users .rhosts or .shosts. */
247 snprintf(buf, sizeof buf, "%.500s/%.100s",
248 pw->pw_dir, rhosts_files[rhosts_file_index]);
249 if (stat(buf, &st) < 0)
250 continue;
251
252 /*
253 * Make sure that the file is either owned by the user or by
254 * root, and make sure it is not writable by anyone but the
255 * owner. This is to help avoid novices accidentally
256 * allowing access to their account by anyone.
257 */
258 if (options.strict_modes &&
259 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
260 (st.st_mode & 022) != 0)) {
261 log("Rhosts authentication refused for %.100s: bad modes for %.200s",
262 pw->pw_name, buf);
263 auth_debug_add("Bad file modes for %.200s", buf);
264 continue;
265 }
266 /* Check if we have been configured to ignore .rhosts and .shosts files. */
267 if (options.ignore_rhosts) {
268 auth_debug_add("Server has been configured to ignore %.100s.",
269 rhosts_files[rhosts_file_index]);
270 continue;
271 }
272 /* Check if authentication is permitted by the file. */
273 if (check_rhosts_file(buf, hostname, ipaddr, client_user, pw->pw_name)) {
274 auth_debug_add("Accepted by %.100s.",
275 rhosts_files[rhosts_file_index]);
276 /* Restore the privileged uid. */
277 restore_uid();
278 auth_debug_add("Accepted host %s ip %s client_user %s server_user %s",
279 hostname, ipaddr, client_user, pw->pw_name);
280 return 1;
281 }
282 }
283
284 /* Restore the privileged uid. */
285 restore_uid();
286 return 0;
287 }
288
289 int
290 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
291 const char *ipaddr)
292 {
293 int ret;
294
295 auth_debug_reset();
296 ret = auth_rhosts2_raw(pw, client_user, hostname, ipaddr);
297 auth_debug_send();
298 return ret;
299 }