1/* $OpenBSD: auth-rhosts.c,v 1.44 2010/03/07 11:57:13 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 */
45extern ServerOptions options;
46extern 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
54static int
55check_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
186int
187auth_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
196static int
197auth_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
316int
317auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
318    const char *ipaddr)
319{
320       return auth_rhosts2_raw(pw, client_user, hostname, ipaddr);
321}
322