xref: /openssh-portable/auth-rhosts.c (revision 4d28fa78)
1 /* $OpenBSD: auth-rhosts.c,v 1.50 2019/06/28 13:35:04 deraadt 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 "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) == -1 &&
226 	    stat(_PATH_SSH_HOSTS_EQUIV, &st) == -1) {
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) == -1) {
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) == -1)
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