1 /* $OpenBSD: auth-rhosts.c,v 1.52 2020/04/17 03:30:05 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 "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 "uidswap.h"
34 #include "pathnames.h"
35 #include "log.h"
36 #include "misc.h"
37 #include "sshbuf.h"
38 #include "sshkey.h"
39 #include "servconf.h"
40 #include "canohost.h"
41 #include "hostfile.h"
42 #include "auth.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 #define RBUFLN 1024
61 char buf[RBUFLN];/* Must not be larger than host, user, dummy below. */
62 int fd;
63 struct stat st;
64
65 /* Open the .rhosts file, deny if unreadable */
66 if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1)
67 return 0;
68 if (fstat(fd, &st) == -1) {
69 close(fd);
70 return 0;
71 }
72 if (!S_ISREG(st.st_mode)) {
73 logit("User %s hosts file %s is not a regular file",
74 server_user, filename);
75 close(fd);
76 return 0;
77 }
78 unset_nonblock(fd);
79 if ((f = fdopen(fd, "r")) == NULL) {
80 close(fd);
81 return 0;
82 }
83 while (fgets(buf, sizeof(buf), f)) {
84 /* All three must have length >= buf to avoid overflows. */
85 char hostbuf[RBUFLN], userbuf[RBUFLN], dummy[RBUFLN];
86 char *host, *user, *cp;
87 int negated;
88
89 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
90 ;
91 if (*cp == '#' || *cp == '\n' || !*cp)
92 continue;
93
94 /*
95 * NO_PLUS is supported at least on OSF/1. We skip it (we
96 * don't ever support the plus syntax).
97 */
98 if (strncmp(cp, "NO_PLUS", 7) == 0)
99 continue;
100
101 /*
102 * This should be safe because each buffer is as big as the
103 * whole string, and thus cannot be overwritten.
104 */
105 switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf,
106 dummy)) {
107 case 0:
108 auth_debug_add("Found empty line in %.100s.", filename);
109 continue;
110 case 1:
111 /* Host name only. */
112 strlcpy(userbuf, server_user, sizeof(userbuf));
113 break;
114 case 2:
115 /* Got both host and user name. */
116 break;
117 case 3:
118 auth_debug_add("Found garbage in %.100s.", filename);
119 continue;
120 default:
121 /* Weird... */
122 continue;
123 }
124
125 host = hostbuf;
126 user = userbuf;
127 negated = 0;
128
129 /* Process negated host names, or positive netgroups. */
130 if (host[0] == '-') {
131 negated = 1;
132 host++;
133 } else if (host[0] == '+')
134 host++;
135
136 if (user[0] == '-') {
137 negated = 1;
138 user++;
139 } else if (user[0] == '+')
140 user++;
141
142 /* Check for empty host/user names (particularly '+'). */
143 if (!host[0] || !user[0]) {
144 /* We come here if either was '+' or '-'. */
145 auth_debug_add("Ignoring wild host/user names "
146 "in %.100s.", filename);
147 continue;
148 }
149 /* Verify that host name matches. */
150 if (host[0] == '@') {
151 if (!innetgr(host + 1, hostname, NULL, NULL) &&
152 !innetgr(host + 1, ipaddr, NULL, NULL))
153 continue;
154 } else if (strcasecmp(host, hostname) &&
155 strcmp(host, ipaddr) != 0)
156 continue; /* Different hostname. */
157
158 /* Verify that user name matches. */
159 if (user[0] == '@') {
160 if (!innetgr(user + 1, NULL, client_user, NULL))
161 continue;
162 } else if (strcmp(user, client_user) != 0)
163 continue; /* Different username. */
164
165 /* Found the user and host. */
166 fclose(f);
167
168 /* If the entry was negated, deny access. */
169 if (negated) {
170 auth_debug_add("Matched negative entry in %.100s.",
171 filename);
172 return 0;
173 }
174 /* Accept authentication. */
175 return 1;
176 }
177
178 /* Authentication using this file denied. */
179 fclose(f);
180 return 0;
181 }
182
183 /*
184 * Tries to authenticate the user using the .shosts or .rhosts file. Returns
185 * true if authentication succeeds. If ignore_rhosts is true, only
186 * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
187 */
188 int
auth_rhosts2(struct passwd * pw,const char * client_user,const char * hostname,const char * ipaddr)189 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
190 const char *ipaddr)
191 {
192 char buf[1024];
193 struct stat st;
194 static const char *rhosts_files[] = {".shosts", ".rhosts", NULL};
195 u_int rhosts_file_index;
196
197 debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s",
198 client_user, hostname, ipaddr);
199
200 /* Switch to the user's uid. */
201 temporarily_use_uid(pw);
202 /*
203 * Quick check: if the user has no .shosts or .rhosts files and
204 * no system hosts.equiv/shosts.equiv files exist then return
205 * failure immediately without doing costly lookups from name
206 * servers.
207 */
208 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
209 rhosts_file_index++) {
210 /* Check users .rhosts or .shosts. */
211 snprintf(buf, sizeof buf, "%.500s/%.100s",
212 pw->pw_dir, rhosts_files[rhosts_file_index]);
213 if (stat(buf, &st) >= 0)
214 break;
215 }
216 /* Switch back to privileged uid. */
217 restore_uid();
218
219 /*
220 * Deny if The user has no .shosts or .rhosts file and there
221 * are no system-wide files.
222 */
223 if (!rhosts_files[rhosts_file_index] &&
224 stat(_PATH_RHOSTS_EQUIV, &st) == -1 &&
225 stat(_PATH_SSH_HOSTS_EQUIV, &st) == -1) {
226 debug3("%s: no hosts access files exist", __func__);
227 return 0;
228 }
229
230 /*
231 * If not logging in as superuser, try /etc/hosts.equiv and
232 * shosts.equiv.
233 */
234 if (pw->pw_uid == 0)
235 debug3("%s: root user, ignoring system hosts files", __func__);
236 else {
237 if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr,
238 client_user, pw->pw_name)) {
239 auth_debug_add("Accepted for %.100s [%.100s] by "
240 "/etc/hosts.equiv.", hostname, ipaddr);
241 return 1;
242 }
243 if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr,
244 client_user, pw->pw_name)) {
245 auth_debug_add("Accepted for %.100s [%.100s] by "
246 "%.100s.", hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV);
247 return 1;
248 }
249 }
250
251 /*
252 * Check that the home directory is owned by root or the user, and is
253 * not group or world writable.
254 */
255 if (stat(pw->pw_dir, &st) == -1) {
256 logit("Rhosts authentication refused for %.100s: "
257 "no home directory %.200s", pw->pw_name, pw->pw_dir);
258 auth_debug_add("Rhosts authentication refused for %.100s: "
259 "no home directory %.200s", pw->pw_name, pw->pw_dir);
260 return 0;
261 }
262 if (options.strict_modes &&
263 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
264 (st.st_mode & 022) != 0)) {
265 logit("Rhosts authentication refused for %.100s: "
266 "bad ownership or modes for home directory.", pw->pw_name);
267 auth_debug_add("Rhosts authentication refused for %.100s: "
268 "bad ownership or modes for home directory.", pw->pw_name);
269 return 0;
270 }
271 /* Temporarily use the user's uid. */
272 temporarily_use_uid(pw);
273
274 /* Check all .rhosts files (currently .shosts and .rhosts). */
275 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
276 rhosts_file_index++) {
277 /* Check users .rhosts or .shosts. */
278 snprintf(buf, sizeof buf, "%.500s/%.100s",
279 pw->pw_dir, rhosts_files[rhosts_file_index]);
280 if (stat(buf, &st) == -1)
281 continue;
282
283 /*
284 * Make sure that the file is either owned by the user or by
285 * root, and make sure it is not writable by anyone but the
286 * owner. This is to help avoid novices accidentally
287 * allowing access to their account by anyone.
288 */
289 if (options.strict_modes &&
290 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
291 (st.st_mode & 022) != 0)) {
292 logit("Rhosts authentication refused for %.100s: bad modes for %.200s",
293 pw->pw_name, buf);
294 auth_debug_add("Bad file modes for %.200s", buf);
295 continue;
296 }
297 /*
298 * Check if we have been configured to ignore .rhosts
299 * and .shosts files.
300 */
301 if (options.ignore_rhosts == IGNORE_RHOSTS_YES ||
302 (options.ignore_rhosts == IGNORE_RHOSTS_SHOSTS &&
303 strcmp(rhosts_files[rhosts_file_index], ".shosts") != 0)) {
304 auth_debug_add("Server has been configured to "
305 "ignore %.100s.", rhosts_files[rhosts_file_index]);
306 continue;
307 }
308 /* Check if authentication is permitted by the file. */
309 if (check_rhosts_file(buf, hostname, ipaddr,
310 client_user, pw->pw_name)) {
311 auth_debug_add("Accepted by %.100s.",
312 rhosts_files[rhosts_file_index]);
313 /* Restore the privileged uid. */
314 restore_uid();
315 auth_debug_add("Accepted host %s ip %s client_user "
316 "%s server_user %s", hostname, ipaddr,
317 client_user, pw->pw_name);
318 return 1;
319 }
320 }
321
322 /* Restore the privileged uid. */
323 restore_uid();
324 return 0;
325 }
326