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1 | /* $OpenBSD: auth-rhosts.c,v 1.43 2008/06/13 14:18:51 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 | #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 "buffer.h" | |
34 | #include "uidswap.h" | |
35 | #include "pathnames.h" | |
36 | #include "log.h" | |
37 | #include "servconf.h" | |
38 | #include "canohost.h" | |
39 | #include "key.h" | |
40 | #include "hostfile.h" | |
41 | #include "auth.h" | |
42 | #include "misc.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 | |
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 | char buf[1024]; /* Must not be larger than host, user, dummy below. */ | |
61 | int fd; | |
62 | struct stat st; | |
63 | ||
64 | /* Open the .rhosts file, deny if unreadable */ | |
65 | if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1) | |
66 | return 0; | |
67 | if (fstat(fd, &st) == -1) { | |
68 | close(fd); | |
69 | return 0; | |
70 | } | |
71 | if (!S_ISREG(st.st_mode)) { | |
72 | logit("User %s hosts file %s is not a regular file", | |
73 | server_user, filename); | |
74 | close(fd); | |
75 | return 0; | |
76 | } | |
77 | unset_nonblock(fd); | |
78 | if ((f = fdopen(fd, "r")) == NULL) { | |
79 | close(fd); | |
80 | return 0; | |
81 | } | |
82 | while (fgets(buf, sizeof(buf), f)) { | |
83 | /* All three must be at least as big as buf to avoid overflows. */ | |
84 | char hostbuf[1024], userbuf[1024], dummy[1024], *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 in %.100s.", | |
144 | 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) && strcmp(host, ipaddr) != 0) | |
153 | continue; /* Different hostname. */ | |
154 | ||
155 | /* Verify that user name matches. */ | |
156 | if (user[0] == '@') { | |
157 | if (!innetgr(user + 1, NULL, client_user, NULL)) | |
158 | continue; | |
159 | } else if (strcmp(user, client_user) != 0) | |
160 | continue; /* Different username. */ | |
161 | ||
162 | /* Found the user and host. */ | |
163 | fclose(f); | |
164 | ||
165 | /* If the entry was negated, deny access. */ | |
166 | if (negated) { | |
167 | auth_debug_add("Matched negative entry in %.100s.", | |
168 | filename); | |
169 | return 0; | |
170 | } | |
171 | /* Accept authentication. */ | |
172 | return 1; | |
173 | } | |
174 | ||
175 | /* Authentication using this file denied. */ | |
176 | fclose(f); | |
177 | return 0; | |
178 | } | |
179 | ||
180 | /* | |
181 | * Tries to authenticate the user using the .shosts or .rhosts file. Returns | |
182 | * true if authentication succeeds. If ignore_rhosts is true, only | |
183 | * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored). | |
184 | */ | |
185 | ||
186 | int | |
187 | auth_rhosts(struct passwd *pw, const char *client_user) | |
188 | { | |
189 | const char *hostname, *ipaddr; | |
190 | ||
191 | hostname = get_canonical_hostname(options.use_dns); | |
192 | ipaddr = get_remote_ipaddr(); | |
193 | return auth_rhosts2(pw, client_user, hostname, ipaddr); | |
194 | } | |
195 | ||
196 | static int | |
197 | auth_rhosts2_raw(struct passwd *pw, const char *client_user, const char *hostname, | |
198 | const char *ipaddr) | |
199 | { | |
200 | char buf[1024]; | |
201 | struct stat st; | |
202 | static const char *rhosts_files[] = {".shosts", ".rhosts", NULL}; | |
203 | u_int rhosts_file_index; | |
204 | ||
205 | debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s", | |
206 | client_user, hostname, ipaddr); | |
207 | ||
208 | /* Switch to the user's uid. */ | |
209 | temporarily_use_uid(pw); | |
210 | /* | |
211 | * Quick check: if the user has no .shosts or .rhosts files, return | |
212 | * failure immediately without doing costly lookups from name | |
213 | * servers. | |
214 | */ | |
215 | for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; | |
216 | rhosts_file_index++) { | |
217 | /* Check users .rhosts or .shosts. */ | |
218 | snprintf(buf, sizeof buf, "%.500s/%.100s", | |
219 | pw->pw_dir, rhosts_files[rhosts_file_index]); | |
220 | if (stat(buf, &st) >= 0) | |
221 | break; | |
222 | } | |
223 | /* Switch back to privileged uid. */ | |
224 | restore_uid(); | |
225 | ||
226 | /* Deny if The user has no .shosts or .rhosts file and there are no system-wide files. */ | |
227 | if (!rhosts_files[rhosts_file_index] && | |
228 | stat(_PATH_RHOSTS_EQUIV, &st) < 0 && | |
229 | stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0) | |
230 | return 0; | |
231 | ||
232 | /* If not logging in as superuser, try /etc/hosts.equiv and shosts.equiv. */ | |
233 | if (pw->pw_uid != 0) { | |
234 | if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr, | |
235 | client_user, pw->pw_name)) { | |
236 | auth_debug_add("Accepted for %.100s [%.100s] by /etc/hosts.equiv.", | |
237 | hostname, ipaddr); | |
238 | return 1; | |
239 | } | |
240 | if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr, | |
241 | client_user, pw->pw_name)) { | |
242 | auth_debug_add("Accepted for %.100s [%.100s] by %.100s.", | |
243 | hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV); | |
244 | return 1; | |
245 | } | |
246 | } | |
247 | /* | |
248 | * Check that the home directory is owned by root or the user, and is | |
249 | * not group or world writable. | |
250 | */ | |
251 | if (stat(pw->pw_dir, &st) < 0) { | |
252 | logit("Rhosts authentication refused for %.100s: " | |
253 | "no home directory %.200s", pw->pw_name, pw->pw_dir); | |
254 | auth_debug_add("Rhosts authentication refused for %.100s: " | |
255 | "no home directory %.200s", pw->pw_name, pw->pw_dir); | |
256 | return 0; | |
257 | } | |
258 | if (options.strict_modes && | |
259 | ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || | |
260 | (st.st_mode & 022) != 0)) { | |
261 | logit("Rhosts authentication refused for %.100s: " | |
262 | "bad ownership or modes for home directory.", pw->pw_name); | |
263 | auth_debug_add("Rhosts authentication refused for %.100s: " | |
264 | "bad ownership or modes for home directory.", pw->pw_name); | |
265 | return 0; | |
266 | } | |
267 | /* Temporarily use the user's uid. */ | |
268 | temporarily_use_uid(pw); | |
269 | ||
270 | /* Check all .rhosts files (currently .shosts and .rhosts). */ | |
271 | for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; | |
272 | rhosts_file_index++) { | |
273 | /* Check users .rhosts or .shosts. */ | |
274 | snprintf(buf, sizeof buf, "%.500s/%.100s", | |
275 | pw->pw_dir, rhosts_files[rhosts_file_index]); | |
276 | if (stat(buf, &st) < 0) | |
277 | continue; | |
278 | ||
279 | /* | |
280 | * Make sure that the file is either owned by the user or by | |
281 | * root, and make sure it is not writable by anyone but the | |
282 | * owner. This is to help avoid novices accidentally | |
283 | * allowing access to their account by anyone. | |
284 | */ | |
285 | if (options.strict_modes && | |
286 | ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || | |
287 | (st.st_mode & 022) != 0)) { | |
288 | logit("Rhosts authentication refused for %.100s: bad modes for %.200s", | |
289 | pw->pw_name, buf); | |
290 | auth_debug_add("Bad file modes for %.200s", buf); | |
291 | continue; | |
292 | } | |
293 | /* Check if we have been configured to ignore .rhosts and .shosts files. */ | |
294 | if (options.ignore_rhosts) { | |
295 | auth_debug_add("Server has been configured to ignore %.100s.", | |
296 | rhosts_files[rhosts_file_index]); | |
297 | continue; | |
298 | } | |
299 | /* Check if authentication is permitted by the file. */ | |
300 | if (check_rhosts_file(buf, hostname, ipaddr, client_user, pw->pw_name)) { | |
301 | auth_debug_add("Accepted by %.100s.", | |
302 | rhosts_files[rhosts_file_index]); | |
303 | /* Restore the privileged uid. */ | |
304 | restore_uid(); | |
305 | auth_debug_add("Accepted host %s ip %s client_user %s server_user %s", | |
306 | hostname, ipaddr, client_user, pw->pw_name); | |
307 | return 1; | |
308 | } | |
309 | } | |
310 | ||
311 | /* Restore the privileged uid. */ | |
312 | restore_uid(); | |
313 | return 0; | |
314 | } | |
315 | ||
316 | int | |
317 | auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname, | |
318 | const char *ipaddr) | |
319 | { | |
320 | int ret; | |
321 | ||
322 | auth_debug_reset(); | |
323 | ret = auth_rhosts2_raw(pw, client_user, hostname, ipaddr); | |
324 | if (!use_privsep) | |
325 | auth_debug_send(); | |
326 | return ret; | |
327 | } |