1 /* $OpenBSD: auth-rhosts.c,v 1.57 2022/12/09 00:17:40 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 #include <errno.h>
23 #include <fcntl.h>
24 #ifdef HAVE_NETGROUP_H
25 # include <netgroup.h>
26 #endif
27 #include <pwd.h>
28 #include <stdio.h>
29 #include <string.h>
30 #include <stdarg.h>
31 #include <stdlib.h>
32 #include <unistd.h>
33
34 #include "packet.h"
35 #include "uidswap.h"
36 #include "pathnames.h"
37 #include "log.h"
38 #include "misc.h"
39 #include "xmalloc.h"
40 #include "sshbuf.h"
41 #include "sshkey.h"
42 #include "servconf.h"
43 #include "canohost.h"
44 #include "hostfile.h"
45 #include "auth.h"
46
47 /* import */
48 extern ServerOptions options;
49 extern int use_privsep;
50
51 /*
52 * This function processes an rhosts-style file (.rhosts, .shosts, or
53 * /etc/hosts.equiv). This returns true if authentication can be granted
54 * based on the file, and returns zero otherwise.
55 */
56
57 static int
check_rhosts_file(const char * filename,const char * hostname,const char * ipaddr,const char * client_user,const char * server_user)58 check_rhosts_file(const char *filename, const char *hostname,
59 const char *ipaddr, const char *client_user,
60 const char *server_user)
61 {
62 FILE *f;
63 #define RBUFLN 1024
64 char buf[RBUFLN];/* Must not be larger than host, user, dummy below. */
65 int fd;
66 struct stat st;
67
68 /* Open the .rhosts file, deny if unreadable */
69 if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1)
70 return 0;
71 if (fstat(fd, &st) == -1) {
72 close(fd);
73 return 0;
74 }
75 if (!S_ISREG(st.st_mode)) {
76 logit("User %s hosts file %s is not a regular file",
77 server_user, filename);
78 close(fd);
79 return 0;
80 }
81 unset_nonblock(fd);
82 if ((f = fdopen(fd, "r")) == NULL) {
83 close(fd);
84 return 0;
85 }
86 while (fgets(buf, sizeof(buf), f)) {
87 /* All three must have length >= buf to avoid overflows. */
88 char hostbuf[RBUFLN], userbuf[RBUFLN], dummy[RBUFLN];
89 char *host, *user, *cp;
90 int negated;
91
92 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
93 ;
94 if (*cp == '#' || *cp == '\n' || !*cp)
95 continue;
96
97 /*
98 * NO_PLUS is supported at least on OSF/1. We skip it (we
99 * don't ever support the plus syntax).
100 */
101 if (strncmp(cp, "NO_PLUS", 7) == 0)
102 continue;
103
104 /*
105 * This should be safe because each buffer is as big as the
106 * whole string, and thus cannot be overwritten.
107 */
108 switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf,
109 dummy)) {
110 case 0:
111 auth_debug_add("Found empty line in %.100s.", filename);
112 continue;
113 case 1:
114 /* Host name only. */
115 strlcpy(userbuf, server_user, sizeof(userbuf));
116 break;
117 case 2:
118 /* Got both host and user name. */
119 break;
120 case 3:
121 auth_debug_add("Found garbage in %.100s.", filename);
122 continue;
123 default:
124 /* Weird... */
125 continue;
126 }
127
128 host = hostbuf;
129 user = userbuf;
130 negated = 0;
131
132 /* Process negated host names, or positive netgroups. */
133 if (host[0] == '-') {
134 negated = 1;
135 host++;
136 } else if (host[0] == '+')
137 host++;
138
139 if (user[0] == '-') {
140 negated = 1;
141 user++;
142 } else if (user[0] == '+')
143 user++;
144
145 /* Check for empty host/user names (particularly '+'). */
146 if (!host[0] || !user[0]) {
147 /* We come here if either was '+' or '-'. */
148 auth_debug_add("Ignoring wild host/user names "
149 "in %.100s.", filename);
150 continue;
151 }
152 /* Verify that host name matches. */
153 if (host[0] == '@') {
154 if (!innetgr(host + 1, hostname, NULL, NULL) &&
155 !innetgr(host + 1, ipaddr, NULL, NULL))
156 continue;
157 } else if (strcasecmp(host, hostname) &&
158 strcmp(host, ipaddr) != 0)
159 continue; /* Different hostname. */
160
161 /* Verify that user name matches. */
162 if (user[0] == '@') {
163 if (!innetgr(user + 1, NULL, client_user, NULL))
164 continue;
165 } else if (strcmp(user, client_user) != 0)
166 continue; /* Different username. */
167
168 /* Found the user and host. */
169 fclose(f);
170
171 /* If the entry was negated, deny access. */
172 if (negated) {
173 auth_debug_add("Matched negative entry in %.100s.",
174 filename);
175 return 0;
176 }
177 /* Accept authentication. */
178 return 1;
179 }
180
181 /* Authentication using this file denied. */
182 fclose(f);
183 return 0;
184 }
185
186 /*
187 * Tries to authenticate the user using the .shosts or .rhosts file. Returns
188 * true if authentication succeeds. If ignore_rhosts is true, only
189 * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
190 */
191 int
auth_rhosts2(struct passwd * pw,const char * client_user,const char * hostname,const char * ipaddr)192 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
193 const char *ipaddr)
194 {
195 char *path = NULL;
196 struct stat st;
197 static const char * const rhosts_files[] = {".shosts", ".rhosts", NULL};
198 u_int rhosts_file_index;
199 int r;
200
201 debug2_f("clientuser %s hostname %s ipaddr %s",
202 client_user, hostname, ipaddr);
203
204 /* Switch to the user's uid. */
205 temporarily_use_uid(pw);
206 /*
207 * Quick check: if the user has no .shosts or .rhosts files and
208 * no system hosts.equiv/shosts.equiv files exist then return
209 * failure immediately without doing costly lookups from name
210 * servers.
211 */
212 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
213 rhosts_file_index++) {
214 /* Check users .rhosts or .shosts. */
215 xasprintf(&path, "%s/%s",
216 pw->pw_dir, rhosts_files[rhosts_file_index]);
217 r = stat(path, &st);
218 free(path);
219 if (r >= 0)
220 break;
221 }
222 /* Switch back to privileged uid. */
223 restore_uid();
224
225 /*
226 * Deny if The user has no .shosts or .rhosts file and there
227 * are no system-wide files.
228 */
229 if (!rhosts_files[rhosts_file_index] &&
230 stat(_PATH_RHOSTS_EQUIV, &st) == -1 &&
231 stat(_PATH_SSH_HOSTS_EQUIV, &st) == -1) {
232 debug3_f("no hosts access files exist");
233 return 0;
234 }
235
236 /*
237 * If not logging in as superuser, try /etc/hosts.equiv and
238 * shosts.equiv.
239 */
240 if (pw->pw_uid == 0)
241 debug3_f("root user, ignoring system hosts files");
242 else {
243 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr,
244 client_user, pw->pw_name)) {
245 auth_debug_add("Accepted for %.100s [%.100s] by "
246 "/etc/hosts.equiv.", hostname, ipaddr);
247 return 1;
248 }
249 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr,
250 client_user, pw->pw_name)) {
251 auth_debug_add("Accepted for %.100s [%.100s] by "
252 "%.100s.", hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV);
253 return 1;
254 }
255 }
256
257 /*
258 * Check that the home directory is owned by root or the user, and is
259 * not group or world writable.
260 */
261 if (stat(pw->pw_dir, &st) == -1) {
262 logit("Rhosts authentication refused for %.100s: "
263 "no home directory %.200s", pw->pw_name, pw->pw_dir);
264 auth_debug_add("Rhosts authentication refused for %.100s: "
265 "no home directory %.200s", pw->pw_name, pw->pw_dir);
266 return 0;
267 }
268 if (options.strict_modes &&
269 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
270 (st.st_mode & 022) != 0)) {
271 logit("Rhosts authentication refused for %.100s: "
272 "bad ownership or modes for home directory.", pw->pw_name);
273 auth_debug_add("Rhosts authentication refused for %.100s: "
274 "bad ownership or modes for home directory.", pw->pw_name);
275 return 0;
276 }
277 /* Temporarily use the user's uid. */
278 temporarily_use_uid(pw);
279
280 /* Check all .rhosts files (currently .shosts and .rhosts). */
281 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
282 rhosts_file_index++) {
283 /* Check users .rhosts or .shosts. */
284 xasprintf(&path, "%s/%s",
285 pw->pw_dir, rhosts_files[rhosts_file_index]);
286 if (stat(path, &st) == -1) {
287 debug3_f("stat %s: %s", path, strerror(errno));
288 free(path);
289 continue;
290 }
291
292 /*
293 * Make sure that the file is either owned by the user or by
294 * root, and make sure it is not writable by anyone but the
295 * owner. This is to help avoid novices accidentally
296 * allowing access to their account by anyone.
297 */
298 if (options.strict_modes &&
299 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
300 (st.st_mode & 022) != 0)) {
301 logit("Rhosts authentication refused for %.100s: "
302 "bad modes for %.200s", pw->pw_name, path);
303 auth_debug_add("Bad file modes for %.200s", path);
304 free(path);
305 continue;
306 }
307 /*
308 * Check if we have been configured to ignore .rhosts
309 * and .shosts files.
310 */
311 if (options.ignore_rhosts == IGNORE_RHOSTS_YES ||
312 (options.ignore_rhosts == IGNORE_RHOSTS_SHOSTS &&
313 strcmp(rhosts_files[rhosts_file_index], ".shosts") != 0)) {
314 auth_debug_add("Server has been configured to "
315 "ignore %.100s.", rhosts_files[rhosts_file_index]);
316 free(path);
317 continue;
318 }
319 /* Check if authentication is permitted by the file. */
320 if (check_rhosts_file(path, hostname, ipaddr,
321 client_user, pw->pw_name)) {
322 auth_debug_add("Accepted by %.100s.",
323 rhosts_files[rhosts_file_index]);
324 /* Restore the privileged uid. */
325 restore_uid();
326 auth_debug_add("Accepted host %s ip %s client_user "
327 "%s server_user %s", hostname, ipaddr,
328 client_user, pw->pw_name);
329 free(path);
330 return 1;
331 }
332 free(path);
333 }
334
335 /* Restore the privileged uid. */
336 restore_uid();
337 return 0;
338 }
339