1 /* $OpenBSD: auth-rhosts.c,v 1.58 2024/05/17 00:30:23 djm 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 <sys/types.h>
18 #include <sys/stat.h>
19
20 #include <errno.h>
21 #include <fcntl.h>
22 #include <netgroup.h>
23 #include <pwd.h>
24 #include <stdio.h>
25 #include <string.h>
26 #include <stdarg.h>
27 #include <stdlib.h>
28 #include <unistd.h>
29
30 #include "packet.h"
31 #include "uidswap.h"
32 #include "pathnames.h"
33 #include "log.h"
34 #include "misc.h"
35 #include "xmalloc.h"
36 #include "sshbuf.h"
37 #include "sshkey.h"
38 #include "servconf.h"
39 #include "canohost.h"
40 #include "hostfile.h"
41 #include "auth.h"
42
43 /* import */
44 extern ServerOptions options;
45
46 /*
47 * This function processes an rhosts-style file (.rhosts, .shosts, or
48 * /etc/hosts.equiv). This returns true if authentication can be granted
49 * based on the file, and returns zero otherwise.
50 */
51
52 static int
check_rhosts_file(const char * filename,const char * hostname,const char * ipaddr,const char * client_user,const char * server_user)53 check_rhosts_file(const char *filename, const char *hostname,
54 const char *ipaddr, const char *client_user,
55 const char *server_user)
56 {
57 FILE *f;
58 #define RBUFLN 1024
59 char buf[RBUFLN];/* Must not be larger than host, user, dummy below. */
60 int fd;
61 struct stat st;
62
63 /* Open the .rhosts file, deny if unreadable */
64 if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1)
65 return 0;
66 if (fstat(fd, &st) == -1) {
67 close(fd);
68 return 0;
69 }
70 if (!S_ISREG(st.st_mode)) {
71 logit("User %s hosts file %s is not a regular file",
72 server_user, filename);
73 close(fd);
74 return 0;
75 }
76 unset_nonblock(fd);
77 if ((f = fdopen(fd, "r")) == NULL) {
78 close(fd);
79 return 0;
80 }
81 while (fgets(buf, sizeof(buf), f)) {
82 /* All three must have length >= buf to avoid overflows. */
83 char hostbuf[RBUFLN], userbuf[RBUFLN], dummy[RBUFLN];
84 char *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 "
144 "in %.100s.", 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) &&
153 strcmp(host, ipaddr) != 0)
154 continue; /* Different hostname. */
155
156 /* Verify that user name matches. */
157 if (user[0] == '@') {
158 if (!innetgr(user + 1, NULL, client_user, NULL))
159 continue;
160 } else if (strcmp(user, client_user) != 0)
161 continue; /* Different username. */
162
163 /* Found the user and host. */
164 fclose(f);
165
166 /* If the entry was negated, deny access. */
167 if (negated) {
168 auth_debug_add("Matched negative entry in %.100s.",
169 filename);
170 return 0;
171 }
172 /* Accept authentication. */
173 return 1;
174 }
175
176 /* Authentication using this file denied. */
177 fclose(f);
178 return 0;
179 }
180
181 /*
182 * Tries to authenticate the user using the .shosts or .rhosts file. Returns
183 * true if authentication succeeds. If ignore_rhosts is true, only
184 * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
185 */
186 int
auth_rhosts2(struct passwd * pw,const char * client_user,const char * hostname,const char * ipaddr)187 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
188 const char *ipaddr)
189 {
190 char *path = NULL;
191 struct stat st;
192 static const char * const rhosts_files[] = {".shosts", ".rhosts", NULL};
193 u_int rhosts_file_index;
194 int r;
195
196 debug2_f("clientuser %s hostname %s ipaddr %s",
197 client_user, hostname, ipaddr);
198
199 /* Switch to the user's uid. */
200 temporarily_use_uid(pw);
201 /*
202 * Quick check: if the user has no .shosts or .rhosts files and
203 * no system hosts.equiv/shosts.equiv files exist then return
204 * failure immediately without doing costly lookups from name
205 * servers.
206 */
207 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
208 rhosts_file_index++) {
209 /* Check users .rhosts or .shosts. */
210 xasprintf(&path, "%s/%s",
211 pw->pw_dir, rhosts_files[rhosts_file_index]);
212 r = stat(path, &st);
213 free(path);
214 if (r >= 0)
215 break;
216 }
217 /* Switch back to privileged uid. */
218 restore_uid();
219
220 /*
221 * Deny if The user has no .shosts or .rhosts file and there
222 * are no system-wide files.
223 */
224 if (!rhosts_files[rhosts_file_index] &&
225 stat(_PATH_RHOSTS_EQUIV, &st) == -1 &&
226 stat(_PATH_SSH_HOSTS_EQUIV, &st) == -1) {
227 debug3_f("no hosts access files exist");
228 return 0;
229 }
230
231 /*
232 * If not logging in as superuser, try /etc/hosts.equiv and
233 * shosts.equiv.
234 */
235 if (pw->pw_uid == 0)
236 debug3_f("root user, ignoring system hosts files");
237 else {
238 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr,
239 client_user, pw->pw_name)) {
240 auth_debug_add("Accepted for %.100s [%.100s] by "
241 "/etc/hosts.equiv.", hostname, ipaddr);
242 return 1;
243 }
244 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr,
245 client_user, pw->pw_name)) {
246 auth_debug_add("Accepted for %.100s [%.100s] by "
247 "%.100s.", hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV);
248 return 1;
249 }
250 }
251
252 /*
253 * Check that the home directory is owned by root or the user, and is
254 * not group or world writable.
255 */
256 if (stat(pw->pw_dir, &st) == -1) {
257 logit("Rhosts authentication refused for %.100s: "
258 "no home directory %.200s", pw->pw_name, pw->pw_dir);
259 auth_debug_add("Rhosts authentication refused for %.100s: "
260 "no home directory %.200s", pw->pw_name, pw->pw_dir);
261 return 0;
262 }
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: "
267 "bad ownership or modes for home directory.", pw->pw_name);
268 auth_debug_add("Rhosts authentication refused for %.100s: "
269 "bad ownership or modes for home directory.", pw->pw_name);
270 return 0;
271 }
272 /* Temporarily use the user's uid. */
273 temporarily_use_uid(pw);
274
275 /* Check all .rhosts files (currently .shosts and .rhosts). */
276 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
277 rhosts_file_index++) {
278 /* Check users .rhosts or .shosts. */
279 xasprintf(&path, "%s/%s",
280 pw->pw_dir, rhosts_files[rhosts_file_index]);
281 if (stat(path, &st) == -1) {
282 debug3_f("stat %s: %s", path, strerror(errno));
283 free(path);
284 continue;
285 }
286
287 /*
288 * Make sure that the file is either owned by the user or by
289 * root, and make sure it is not writable by anyone but the
290 * owner. This is to help avoid novices accidentally
291 * allowing access to their account by anyone.
292 */
293 if (options.strict_modes &&
294 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
295 (st.st_mode & 022) != 0)) {
296 logit("Rhosts authentication refused for %.100s: "
297 "bad modes for %.200s", pw->pw_name, path);
298 auth_debug_add("Bad file modes for %.200s", path);
299 free(path);
300 continue;
301 }
302 /*
303 * Check if we have been configured to ignore .rhosts
304 * and .shosts files.
305 */
306 if (options.ignore_rhosts == IGNORE_RHOSTS_YES ||
307 (options.ignore_rhosts == IGNORE_RHOSTS_SHOSTS &&
308 strcmp(rhosts_files[rhosts_file_index], ".shosts") != 0)) {
309 auth_debug_add("Server has been configured to "
310 "ignore %.100s.", rhosts_files[rhosts_file_index]);
311 free(path);
312 continue;
313 }
314 /* Check if authentication is permitted by the file. */
315 if (check_rhosts_file(path, hostname, ipaddr,
316 client_user, pw->pw_name)) {
317 auth_debug_add("Accepted by %.100s.",
318 rhosts_files[rhosts_file_index]);
319 /* Restore the privileged uid. */
320 restore_uid();
321 auth_debug_add("Accepted host %s ip %s client_user "
322 "%s server_user %s", hostname, ipaddr,
323 client_user, pw->pw_name);
324 free(path);
325 return 1;
326 }
327 free(path);
328 }
329
330 /* Restore the privileged uid. */
331 restore_uid();
332 return 0;
333 }
334