auth-rhosts.c revision 323134 
1/* $OpenBSD: auth-rhosts.c,v 1.48 2016/08/13 17:47:41 markus 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 "buffer.h" /* XXX */
38#include "key.h" /* XXX */
39#include "servconf.h"
40#include "canohost.h"
41#include "sshkey.h"
42#include "hostfile.h"
43#include "auth.h"
44
45/* import */
46extern ServerOptions options;
47extern 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
55static int
56check_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 */
189int
190auth_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) < 0 &&
226	    stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0) {
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) < 0) {
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) < 0)
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