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3c0ef626 | 1 | /* |
2 | * Author: Tatu Ylonen <ylo@cs.hut.fi> | |
3 | * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland | |
4 | * All rights reserved | |
5 | * Rhosts authentication. This file contains code to check whether to admit | |
6 | * the login based on rhosts authentication. This file also processes | |
7 | * /etc/hosts.equiv. | |
8 | * | |
9 | * As far as I am concerned, the code I have written for this software | |
10 | * can be used freely for any purpose. Any derived versions of this | |
11 | * software must be clearly marked as such, and if the derived work is | |
12 | * incompatible with the protocol description in the RFC file, it must be | |
13 | * called by a name other than "ssh" or "Secure Shell". | |
14 | */ | |
15 | ||
16 | #include "includes.h" | |
17 | RCSID("$OpenBSD: auth-rhosts.c,v 1.24 2001/06/23 15:12:17 itojun Exp $"); | |
18 | ||
19 | #include "packet.h" | |
20 | #include "xmalloc.h" | |
21 | #include "uidswap.h" | |
22 | #include "pathnames.h" | |
23 | #include "log.h" | |
24 | #include "servconf.h" | |
25 | #include "canohost.h" | |
26 | #include "auth.h" | |
27 | ||
28 | /* import */ | |
29 | extern ServerOptions options; | |
30 | ||
31 | /* | |
32 | * This function processes an rhosts-style file (.rhosts, .shosts, or | |
33 | * /etc/hosts.equiv). This returns true if authentication can be granted | |
34 | * based on the file, and returns zero otherwise. | |
35 | */ | |
36 | ||
37 | static int | |
38 | check_rhosts_file(const char *filename, const char *hostname, | |
39 | const char *ipaddr, const char *client_user, | |
40 | const char *server_user) | |
41 | { | |
42 | FILE *f; | |
43 | char buf[1024]; /* Must not be larger than host, user, dummy below. */ | |
44 | ||
45 | /* Open the .rhosts file, deny if unreadable */ | |
46 | f = fopen(filename, "r"); | |
47 | if (!f) | |
48 | return 0; | |
49 | ||
50 | while (fgets(buf, sizeof(buf), f)) { | |
51 | /* All three must be at least as big as buf to avoid overflows. */ | |
52 | char hostbuf[1024], userbuf[1024], dummy[1024], *host, *user, *cp; | |
53 | int negated; | |
54 | ||
55 | for (cp = buf; *cp == ' ' || *cp == '\t'; cp++) | |
56 | ; | |
57 | if (*cp == '#' || *cp == '\n' || !*cp) | |
58 | continue; | |
59 | ||
60 | /* | |
61 | * NO_PLUS is supported at least on OSF/1. We skip it (we | |
62 | * don't ever support the plus syntax). | |
63 | */ | |
64 | if (strncmp(cp, "NO_PLUS", 7) == 0) | |
65 | continue; | |
66 | ||
67 | /* | |
68 | * This should be safe because each buffer is as big as the | |
69 | * whole string, and thus cannot be overwritten. | |
70 | */ | |
71 | switch (sscanf(buf, "%s %s %s", hostbuf, userbuf, dummy)) { | |
72 | case 0: | |
73 | packet_send_debug("Found empty line in %.100s.", filename); | |
74 | continue; | |
75 | case 1: | |
76 | /* Host name only. */ | |
77 | strlcpy(userbuf, server_user, sizeof(userbuf)); | |
78 | break; | |
79 | case 2: | |
80 | /* Got both host and user name. */ | |
81 | break; | |
82 | case 3: | |
83 | packet_send_debug("Found garbage in %.100s.", filename); | |
84 | continue; | |
85 | default: | |
86 | /* Weird... */ | |
87 | continue; | |
88 | } | |
89 | ||
90 | host = hostbuf; | |
91 | user = userbuf; | |
92 | negated = 0; | |
93 | ||
94 | /* Process negated host names, or positive netgroups. */ | |
95 | if (host[0] == '-') { | |
96 | negated = 1; | |
97 | host++; | |
98 | } else if (host[0] == '+') | |
99 | host++; | |
100 | ||
101 | if (user[0] == '-') { | |
102 | negated = 1; | |
103 | user++; | |
104 | } else if (user[0] == '+') | |
105 | user++; | |
106 | ||
107 | /* Check for empty host/user names (particularly '+'). */ | |
108 | if (!host[0] || !user[0]) { | |
109 | /* We come here if either was '+' or '-'. */ | |
110 | packet_send_debug("Ignoring wild host/user names in %.100s.", | |
111 | filename); | |
112 | continue; | |
113 | } | |
114 | /* Verify that host name matches. */ | |
115 | if (host[0] == '@') { | |
116 | if (!innetgr(host + 1, hostname, NULL, NULL) && | |
117 | !innetgr(host + 1, ipaddr, NULL, NULL)) | |
118 | continue; | |
119 | } else if (strcasecmp(host, hostname) && strcmp(host, ipaddr) != 0) | |
120 | continue; /* Different hostname. */ | |
121 | ||
122 | /* Verify that user name matches. */ | |
123 | if (user[0] == '@') { | |
124 | if (!innetgr(user + 1, NULL, client_user, NULL)) | |
125 | continue; | |
126 | } else if (strcmp(user, client_user) != 0) | |
127 | continue; /* Different username. */ | |
128 | ||
129 | /* Found the user and host. */ | |
130 | fclose(f); | |
131 | ||
132 | /* If the entry was negated, deny access. */ | |
133 | if (negated) { | |
134 | packet_send_debug("Matched negative entry in %.100s.", | |
135 | filename); | |
136 | return 0; | |
137 | } | |
138 | /* Accept authentication. */ | |
139 | return 1; | |
140 | } | |
141 | ||
142 | /* Authentication using this file denied. */ | |
143 | fclose(f); | |
144 | return 0; | |
145 | } | |
146 | ||
147 | /* | |
148 | * Tries to authenticate the user using the .shosts or .rhosts file. Returns | |
149 | * true if authentication succeeds. If ignore_rhosts is true, only | |
150 | * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored). | |
151 | */ | |
152 | ||
153 | int | |
154 | auth_rhosts(struct passwd *pw, const char *client_user) | |
155 | { | |
156 | const char *hostname, *ipaddr; | |
157 | int ret; | |
158 | ||
159 | hostname = get_canonical_hostname(options.reverse_mapping_check); | |
160 | ipaddr = get_remote_ipaddr(); | |
161 | ret = auth_rhosts2(pw, client_user, hostname, ipaddr); | |
162 | return ret; | |
163 | } | |
164 | ||
165 | int | |
166 | auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname, | |
167 | const char *ipaddr) | |
168 | { | |
169 | char buf[1024]; | |
170 | struct stat st; | |
171 | static const char *rhosts_files[] = {".shosts", ".rhosts", NULL}; | |
172 | u_int rhosts_file_index; | |
173 | ||
174 | debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s", | |
175 | client_user, hostname, ipaddr); | |
176 | ||
177 | /* no user given */ | |
178 | if (pw == NULL) | |
179 | return 0; | |
180 | ||
181 | /* Switch to the user's uid. */ | |
182 | temporarily_use_uid(pw); | |
183 | /* | |
184 | * Quick check: if the user has no .shosts or .rhosts files, return | |
185 | * failure immediately without doing costly lookups from name | |
186 | * servers. | |
187 | */ | |
188 | for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; | |
189 | rhosts_file_index++) { | |
190 | /* Check users .rhosts or .shosts. */ | |
191 | snprintf(buf, sizeof buf, "%.500s/%.100s", | |
192 | pw->pw_dir, rhosts_files[rhosts_file_index]); | |
193 | if (stat(buf, &st) >= 0) | |
194 | break; | |
195 | } | |
196 | /* Switch back to privileged uid. */ | |
197 | restore_uid(); | |
198 | ||
199 | /* Deny if The user has no .shosts or .rhosts file and there are no system-wide files. */ | |
200 | if (!rhosts_files[rhosts_file_index] && | |
201 | stat(_PATH_RHOSTS_EQUIV, &st) < 0 && | |
202 | stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0) | |
203 | return 0; | |
204 | ||
205 | /* If not logging in as superuser, try /etc/hosts.equiv and shosts.equiv. */ | |
206 | if (pw->pw_uid != 0) { | |
207 | if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr, client_user, | |
208 | pw->pw_name)) { | |
209 | packet_send_debug("Accepted for %.100s [%.100s] by /etc/hosts.equiv.", | |
210 | hostname, ipaddr); | |
211 | return 1; | |
212 | } | |
213 | if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr, client_user, | |
214 | pw->pw_name)) { | |
215 | packet_send_debug("Accepted for %.100s [%.100s] by %.100s.", | |
216 | hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV); | |
217 | return 1; | |
218 | } | |
219 | } | |
220 | /* | |
221 | * Check that the home directory is owned by root or the user, and is | |
222 | * not group or world writable. | |
223 | */ | |
224 | if (stat(pw->pw_dir, &st) < 0) { | |
225 | log("Rhosts authentication refused for %.100s: no home directory %.200s", | |
226 | pw->pw_name, pw->pw_dir); | |
227 | packet_send_debug("Rhosts authentication refused for %.100s: no home directory %.200s", | |
228 | pw->pw_name, pw->pw_dir); | |
229 | return 0; | |
230 | } | |
231 | if (options.strict_modes && | |
232 | ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || | |
233 | (st.st_mode & 022) != 0)) { | |
234 | log("Rhosts authentication refused for %.100s: bad ownership or modes for home directory.", | |
235 | pw->pw_name); | |
236 | packet_send_debug("Rhosts authentication refused for %.100s: bad ownership or modes for home directory.", | |
237 | pw->pw_name); | |
238 | return 0; | |
239 | } | |
240 | /* Temporarily use the user's uid. */ | |
241 | temporarily_use_uid(pw); | |
242 | ||
243 | /* Check all .rhosts files (currently .shosts and .rhosts). */ | |
244 | for (rhosts_file_index = 0; rhosts_files[rhosts_file_index]; | |
245 | rhosts_file_index++) { | |
246 | /* Check users .rhosts or .shosts. */ | |
247 | snprintf(buf, sizeof buf, "%.500s/%.100s", | |
248 | pw->pw_dir, rhosts_files[rhosts_file_index]); | |
249 | if (stat(buf, &st) < 0) | |
250 | continue; | |
251 | ||
252 | /* | |
253 | * Make sure that the file is either owned by the user or by | |
254 | * root, and make sure it is not writable by anyone but the | |
255 | * owner. This is to help avoid novices accidentally | |
256 | * allowing access to their account by anyone. | |
257 | */ | |
258 | if (options.strict_modes && | |
259 | ((st.st_uid != 0 && st.st_uid != pw->pw_uid) || | |
260 | (st.st_mode & 022) != 0)) { | |
261 | log("Rhosts authentication refused for %.100s: bad modes for %.200s", | |
262 | pw->pw_name, buf); | |
263 | packet_send_debug("Bad file modes for %.200s", buf); | |
264 | continue; | |
265 | } | |
266 | /* Check if we have been configured to ignore .rhosts and .shosts files. */ | |
267 | if (options.ignore_rhosts) { | |
268 | packet_send_debug("Server has been configured to ignore %.100s.", | |
269 | rhosts_files[rhosts_file_index]); | |
270 | continue; | |
271 | } | |
272 | /* Check if authentication is permitted by the file. */ | |
273 | if (check_rhosts_file(buf, hostname, ipaddr, client_user, pw->pw_name)) { | |
274 | packet_send_debug("Accepted by %.100s.", | |
275 | rhosts_files[rhosts_file_index]); | |
276 | /* Restore the privileged uid. */ | |
277 | restore_uid(); | |
278 | return 1; | |
279 | } | |
280 | } | |
281 | ||
282 | /* Restore the privileged uid. */ | |
283 | restore_uid(); | |
284 | return 0; | |
285 | } |