1 /* $OpenBSD: auth-rhosts.c,v 1.48 2016/08/13 17:47:41 markus 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 "buffer.h" /* XXX */
38 #include "key.h" /* XXX */
39 #include "servconf.h"
40 #include "canohost.h"
41 #include "sshkey.h"
42 #include "hostfile.h"
43 #include "auth.h"
44
45 /* import */
46 extern ServerOptions options;
47 extern int use_privsep;
48
49 /*
50 * This function processes an rhosts-style file (.rhosts, .shosts, or
51 * /etc/hosts.equiv). This returns true if authentication can be granted
52 * based on the file, and returns zero otherwise.
53 */
54
55 static int
check_rhosts_file(const char * filename,const char * hostname,const char * ipaddr,const char * client_user,const char * server_user)56 check_rhosts_file(const char *filename, const char *hostname,
57 const char *ipaddr, const char *client_user,
58 const char *server_user)
59 {
60 FILE *f;
61 #define RBUFLN 1024
62 char buf[RBUFLN];/* Must not be larger than host, user, dummy below. */
63 int fd;
64 struct stat st;
65
66 /* Open the .rhosts file, deny if unreadable */
67 if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1)
68 return 0;
69 if (fstat(fd, &st) == -1) {
70 close(fd);
71 return 0;
72 }
73 if (!S_ISREG(st.st_mode)) {
74 logit("User %s hosts file %s is not a regular file",
75 server_user, filename);
76 close(fd);
77 return 0;
78 }
79 unset_nonblock(fd);
80 if ((f = fdopen(fd, "r")) == NULL) {
81 close(fd);
82 return 0;
83 }
84 while (fgets(buf, sizeof(buf), f)) {
85 /* All three must have length >= buf to avoid overflows. */
86 char hostbuf[RBUFLN], userbuf[RBUFLN], dummy[RBUFLN];
87 char *host, *user, *cp;
88 int negated;
89
90 for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
91 ;
92 if (*cp == '#' || *cp == '\n' || !*cp)
93 continue;
94
95 /*
96 * NO_PLUS is supported at least on OSF/1. We skip it (we
97 * don't ever support the plus syntax).
98 */
99 if (strncmp(cp, "NO_PLUS", 7) == 0)
100 continue;
101
102 /*
103 * This should be safe because each buffer is as big as the
104 * whole string, and thus cannot be overwritten.
105 */
106 switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf,
107 dummy)) {
108 case 0:
109 auth_debug_add("Found empty line in %.100s.", filename);
110 continue;
111 case 1:
112 /* Host name only. */
113 strlcpy(userbuf, server_user, sizeof(userbuf));
114 break;
115 case 2:
116 /* Got both host and user name. */
117 break;
118 case 3:
119 auth_debug_add("Found garbage in %.100s.", filename);
120 continue;
121 default:
122 /* Weird... */
123 continue;
124 }
125
126 host = hostbuf;
127 user = userbuf;
128 negated = 0;
129
130 /* Process negated host names, or positive netgroups. */
131 if (host[0] == '-') {
132 negated = 1;
133 host++;
134 } else if (host[0] == '+')
135 host++;
136
137 if (user[0] == '-') {
138 negated = 1;
139 user++;
140 } else if (user[0] == '+')
141 user++;
142
143 /* Check for empty host/user names (particularly '+'). */
144 if (!host[0] || !user[0]) {
145 /* We come here if either was '+' or '-'. */
146 auth_debug_add("Ignoring wild host/user names "
147 "in %.100s.", filename);
148 continue;
149 }
150 /* Verify that host name matches. */
151 if (host[0] == '@') {
152 if (!innetgr(host + 1, hostname, NULL, NULL) &&
153 !innetgr(host + 1, ipaddr, NULL, NULL))
154 continue;
155 } else if (strcasecmp(host, hostname) &&
156 strcmp(host, ipaddr) != 0)
157 continue; /* Different hostname. */
158
159 /* Verify that user name matches. */
160 if (user[0] == '@') {
161 if (!innetgr(user + 1, NULL, client_user, NULL))
162 continue;
163 } else if (strcmp(user, client_user) != 0)
164 continue; /* Different username. */
165
166 /* Found the user and host. */
167 fclose(f);
168
169 /* If the entry was negated, deny access. */
170 if (negated) {
171 auth_debug_add("Matched negative entry in %.100s.",
172 filename);
173 return 0;
174 }
175 /* Accept authentication. */
176 return 1;
177 }
178
179 /* Authentication using this file denied. */
180 fclose(f);
181 return 0;
182 }
183
184 /*
185 * Tries to authenticate the user using the .shosts or .rhosts file. Returns
186 * true if authentication succeeds. If ignore_rhosts is true, only
187 * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
188 */
189 int
auth_rhosts2(struct passwd * pw,const char * client_user,const char * hostname,const char * ipaddr)190 auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
191 const char *ipaddr)
192 {
193 char buf[1024];
194 struct stat st;
195 static const char *rhosts_files[] = {".shosts", ".rhosts", NULL};
196 u_int rhosts_file_index;
197
198 debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s",
199 client_user, hostname, ipaddr);
200
201 /* Switch to the user's uid. */
202 temporarily_use_uid(pw);
203 /*
204 * Quick check: if the user has no .shosts or .rhosts files and
205 * no system hosts.equiv/shosts.equiv files exist then return
206 * failure immediately without doing costly lookups from name
207 * servers.
208 */
209 for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
210 rhosts_file_index++) {
211 /* Check users .rhosts or .shosts. */
212 snprintf(buf, sizeof buf, "%.500s/%.100s",
213 pw->pw_dir, rhosts_files[rhosts_file_index]);
214 if (stat(buf, &st) >= 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) < 0 &&
226 stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0) {
227 debug3("%s: no hosts access files exist", __func__);
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("%s: root user, ignoring system hosts files", __func__);
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) < 0) {
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 snprintf(buf, sizeof buf, "%.500s/%.100s",
280 pw->pw_dir, rhosts_files[rhosts_file_index]);
281 if (stat(buf, &st) < 0)
282 continue;
283
284 /*
285 * Make sure that the file is either owned by the user or by
286 * root, and make sure it is not writable by anyone but the
287 * owner. This is to help avoid novices accidentally
288 * allowing access to their account by anyone.
289 */
290 if (options.strict_modes &&
291 ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
292 (st.st_mode & 022) != 0)) {
293 logit("Rhosts authentication refused for %.100s: bad modes for %.200s",
294 pw->pw_name, buf);
295 auth_debug_add("Bad file modes for %.200s", buf);
296 continue;
297 }
298 /*
299 * Check if we have been configured to ignore .rhosts
300 * and .shosts files.
301 */
302 if (options.ignore_rhosts) {
303 auth_debug_add("Server has been configured to "
304 "ignore %.100s.", rhosts_files[rhosts_file_index]);
305 continue;
306 }
307 /* Check if authentication is permitted by the file. */
308 if (check_rhosts_file(buf, hostname, ipaddr,
309 client_user, pw->pw_name)) {
310 auth_debug_add("Accepted by %.100s.",
311 rhosts_files[rhosts_file_index]);
312 /* Restore the privileged uid. */
313 restore_uid();
314 auth_debug_add("Accepted host %s ip %s client_user "
315 "%s server_user %s", hostname, ipaddr,
316 client_user, pw->pw_name);
317 return 1;
318 }
319 }
320
321 /* Restore the privileged uid. */
322 restore_uid();
323 return 0;
324 }
325