auth-rhosts.c revision 295367 
1/* $OpenBSD: auth-rhosts.c,v 1.46 2014/12/23 22:42:48 djm 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 "misc.h"
38#include "servconf.h"
39#include "canohost.h"
40#include "key.h"
41#include "hostfile.h"
42#include "auth.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#define RBUFLN 1024
61	char buf[RBUFLN];/* Must not be larger than host, user, dummy below. */
62	int fd;
63	struct stat st;
64
65	/* Open the .rhosts file, deny if unreadable */
66	if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1)
67		return 0;
68	if (fstat(fd, &st) == -1) {
69		close(fd);
70		return 0;
71	}
72	if (!S_ISREG(st.st_mode)) {
73		logit("User %s hosts file %s is not a regular file",
74		    server_user, filename);
75		close(fd);
76		return 0;
77	}
78	unset_nonblock(fd);
79	if ((f = fdopen(fd, "r")) == NULL) {
80		close(fd);
81		return 0;
82	}
83	while (fgets(buf, sizeof(buf), f)) {
84		/* All three must have length >= buf to avoid overflows. */
85		char hostbuf[RBUFLN], userbuf[RBUFLN], dummy[RBUFLN];
86		char *host, *user, *cp;
87		int negated;
88
89		for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
90			;
91		if (*cp == '#' || *cp == '\n' || !*cp)
92			continue;
93
94		/*
95		 * NO_PLUS is supported at least on OSF/1.  We skip it (we
96		 * don't ever support the plus syntax).
97		 */
98		if (strncmp(cp, "NO_PLUS", 7) == 0)
99			continue;
100
101		/*
102		 * This should be safe because each buffer is as big as the
103		 * whole string, and thus cannot be overwritten.
104		 */
105		switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf,
106		    dummy)) {
107		case 0:
108			auth_debug_add("Found empty line in %.100s.", filename);
109			continue;
110		case 1:
111			/* Host name only. */
112			strlcpy(userbuf, server_user, sizeof(userbuf));
113			break;
114		case 2:
115			/* Got both host and user name. */
116			break;
117		case 3:
118			auth_debug_add("Found garbage in %.100s.", filename);
119			continue;
120		default:
121			/* Weird... */
122			continue;
123		}
124
125		host = hostbuf;
126		user = userbuf;
127		negated = 0;
128
129		/* Process negated host names, or positive netgroups. */
130		if (host[0] == '-') {
131			negated = 1;
132			host++;
133		} else if (host[0] == '+')
134			host++;
135
136		if (user[0] == '-') {
137			negated = 1;
138			user++;
139		} else if (user[0] == '+')
140			user++;
141
142		/* Check for empty host/user names (particularly '+'). */
143		if (!host[0] || !user[0]) {
144			/* We come here if either was '+' or '-'. */
145			auth_debug_add("Ignoring wild host/user names "
146			    "in %.100s.", filename);
147			continue;
148		}
149		/* Verify that host name matches. */
150		if (host[0] == '@') {
151			if (!innetgr(host + 1, hostname, NULL, NULL) &&
152			    !innetgr(host + 1, ipaddr, NULL, NULL))
153				continue;
154		} else if (strcasecmp(host, hostname) &&
155		    strcmp(host, ipaddr) != 0)
156			continue;	/* Different hostname. */
157
158		/* Verify that user name matches. */
159		if (user[0] == '@') {
160			if (!innetgr(user + 1, NULL, client_user, NULL))
161				continue;
162		} else if (strcmp(user, client_user) != 0)
163			continue;	/* Different username. */
164
165		/* Found the user and host. */
166		fclose(f);
167
168		/* If the entry was negated, deny access. */
169		if (negated) {
170			auth_debug_add("Matched negative entry in %.100s.",
171			    filename);
172			return 0;
173		}
174		/* Accept authentication. */
175		return 1;
176	}
177
178	/* Authentication using this file denied. */
179	fclose(f);
180	return 0;
181}
182
183/*
184 * Tries to authenticate the user using the .shosts or .rhosts file. Returns
185 * true if authentication succeeds.  If ignore_rhosts is true, only
186 * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
187 */
188
189int
190auth_rhosts(struct passwd *pw, const char *client_user)
191{
192	const char *hostname, *ipaddr;
193
194	hostname = get_canonical_hostname(options.use_dns);
195	ipaddr = get_remote_ipaddr();
196	return auth_rhosts2(pw, client_user, hostname, ipaddr);
197}
198
199static int
200auth_rhosts2_raw(struct passwd *pw, const char *client_user, const char *hostname,
201    const char *ipaddr)
202{
203	char buf[1024];
204	struct stat st;
205	static const char *rhosts_files[] = {".shosts", ".rhosts", NULL};
206	u_int rhosts_file_index;
207
208	debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s",
209	    client_user, hostname, ipaddr);
210
211	/* Switch to the user's uid. */
212	temporarily_use_uid(pw);
213	/*
214	 * Quick check: if the user has no .shosts or .rhosts files and
215	 * no system hosts.equiv/shosts.equiv files exist then return
216	 * failure immediately without doing costly lookups from name
217	 * servers.
218	 */
219	for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
220	    rhosts_file_index++) {
221		/* Check users .rhosts or .shosts. */
222		snprintf(buf, sizeof buf, "%.500s/%.100s",
223			 pw->pw_dir, rhosts_files[rhosts_file_index]);
224		if (stat(buf, &st) >= 0)
225			break;
226	}
227	/* Switch back to privileged uid. */
228	restore_uid();
229
230	/*
231	 * Deny if The user has no .shosts or .rhosts file and there
232	 * are no system-wide files.
233	 */
234	if (!rhosts_files[rhosts_file_index] &&
235	    stat(_PATH_RHOSTS_EQUIV, &st) < 0 &&
236	    stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0) {
237		debug3("%s: no hosts access files exist", __func__);
238		return 0;
239	}
240
241	/*
242	 * If not logging in as superuser, try /etc/hosts.equiv and
243	 * shosts.equiv.
244	 */
245	if (pw->pw_uid == 0)
246		debug3("%s: root user, ignoring system hosts files", __func__);
247	else {
248		if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr,
249		    client_user, pw->pw_name)) {
250			auth_debug_add("Accepted for %.100s [%.100s] by "
251			    "/etc/hosts.equiv.", hostname, ipaddr);
252			return 1;
253		}
254		if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr,
255		    client_user, pw->pw_name)) {
256			auth_debug_add("Accepted for %.100s [%.100s] by "
257			    "%.100s.", hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV);
258			return 1;
259		}
260	}
261
262	/*
263	 * Check that the home directory is owned by root or the user, and is
264	 * not group or world writable.
265	 */
266	if (stat(pw->pw_dir, &st) < 0) {
267		logit("Rhosts authentication refused for %.100s: "
268		    "no home directory %.200s", pw->pw_name, pw->pw_dir);
269		auth_debug_add("Rhosts authentication refused for %.100s: "
270		    "no home directory %.200s", pw->pw_name, pw->pw_dir);
271		return 0;
272	}
273	if (options.strict_modes &&
274	    ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
275	    (st.st_mode & 022) != 0)) {
276		logit("Rhosts authentication refused for %.100s: "
277		    "bad ownership or modes for home directory.", pw->pw_name);
278		auth_debug_add("Rhosts authentication refused for %.100s: "
279		    "bad ownership or modes for home directory.", pw->pw_name);
280		return 0;
281	}
282	/* Temporarily use the user's uid. */
283	temporarily_use_uid(pw);
284
285	/* Check all .rhosts files (currently .shosts and .rhosts). */
286	for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
287	    rhosts_file_index++) {
288		/* Check users .rhosts or .shosts. */
289		snprintf(buf, sizeof buf, "%.500s/%.100s",
290			 pw->pw_dir, rhosts_files[rhosts_file_index]);
291		if (stat(buf, &st) < 0)
292			continue;
293
294		/*
295		 * Make sure that the file is either owned by the user or by
296		 * root, and make sure it is not writable by anyone but the
297		 * owner.  This is to help avoid novices accidentally
298		 * allowing access to their account by anyone.
299		 */
300		if (options.strict_modes &&
301		    ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
302		    (st.st_mode & 022) != 0)) {
303			logit("Rhosts authentication refused for %.100s: bad modes for %.200s",
304			    pw->pw_name, buf);
305			auth_debug_add("Bad file modes for %.200s", buf);
306			continue;
307		}
308		/*
309		 * Check if we have been configured to ignore .rhosts
310		 * and .shosts files.
311		 */
312		if (options.ignore_rhosts) {
313			auth_debug_add("Server has been configured to "
314			    "ignore %.100s.", rhosts_files[rhosts_file_index]);
315			continue;
316		}
317		/* Check if authentication is permitted by the file. */
318		if (check_rhosts_file(buf, hostname, ipaddr,
319		    client_user, pw->pw_name)) {
320			auth_debug_add("Accepted by %.100s.",
321			    rhosts_files[rhosts_file_index]);
322			/* Restore the privileged uid. */
323			restore_uid();
324			auth_debug_add("Accepted host %s ip %s client_user "
325			    "%s server_user %s", hostname, ipaddr,
326			    client_user, pw->pw_name);
327			return 1;
328		}
329	}
330
331	/* Restore the privileged uid. */
332	restore_uid();
333	return 0;
334}
335
336int
337auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
338    const char *ipaddr)
339{
340       return auth_rhosts2_raw(pw, client_user, hostname, ipaddr);
341}
342