1/* $OpenBSD: auth-rhosts.c,v 1.57 2022/12/09 00:17:40 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#include <errno.h>
23#include <fcntl.h>
24#ifdef HAVE_NETGROUP_H
25# include <netgroup.h>
26#endif
27#include <pwd.h>
28#include <stdio.h>
29#include <string.h>
30#include <stdarg.h>
31#include <stdlib.h>
32#include <unistd.h>
33
34#include "packet.h"
35#include "uidswap.h"
36#include "pathnames.h"
37#include "log.h"
38#include "misc.h"
39#include "xmalloc.h"
40#include "sshbuf.h"
41#include "sshkey.h"
42#include "servconf.h"
43#include "canohost.h"
44#include "hostfile.h"
45#include "auth.h"
46
47/* import */
48extern ServerOptions options;
49extern int use_privsep;
50
51/*
52 * This function processes an rhosts-style file (.rhosts, .shosts, or
53 * /etc/hosts.equiv).  This returns true if authentication can be granted
54 * based on the file, and returns zero otherwise.
55 */
56
57static int
58check_rhosts_file(const char *filename, const char *hostname,
59		  const char *ipaddr, const char *client_user,
60		  const char *server_user)
61{
62	FILE *f;
63#define RBUFLN 1024
64	char buf[RBUFLN];/* Must not be larger than host, user, dummy below. */
65	int fd;
66	struct stat st;
67
68	/* Open the .rhosts file, deny if unreadable */
69	if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1)
70		return 0;
71	if (fstat(fd, &st) == -1) {
72		close(fd);
73		return 0;
74	}
75	if (!S_ISREG(st.st_mode)) {
76		logit("User %s hosts file %s is not a regular file",
77		    server_user, filename);
78		close(fd);
79		return 0;
80	}
81	unset_nonblock(fd);
82	if ((f = fdopen(fd, "r")) == NULL) {
83		close(fd);
84		return 0;
85	}
86	while (fgets(buf, sizeof(buf), f)) {
87		/* All three must have length >= buf to avoid overflows. */
88		char hostbuf[RBUFLN], userbuf[RBUFLN], dummy[RBUFLN];
89		char *host, *user, *cp;
90		int negated;
91
92		for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
93			;
94		if (*cp == '#' || *cp == '\n' || !*cp)
95			continue;
96
97		/*
98		 * NO_PLUS is supported at least on OSF/1.  We skip it (we
99		 * don't ever support the plus syntax).
100		 */
101		if (strncmp(cp, "NO_PLUS", 7) == 0)
102			continue;
103
104		/*
105		 * This should be safe because each buffer is as big as the
106		 * whole string, and thus cannot be overwritten.
107		 */
108		switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf,
109		    dummy)) {
110		case 0:
111			auth_debug_add("Found empty line in %.100s.", filename);
112			continue;
113		case 1:
114			/* Host name only. */
115			strlcpy(userbuf, server_user, sizeof(userbuf));
116			break;
117		case 2:
118			/* Got both host and user name. */
119			break;
120		case 3:
121			auth_debug_add("Found garbage in %.100s.", filename);
122			continue;
123		default:
124			/* Weird... */
125			continue;
126		}
127
128		host = hostbuf;
129		user = userbuf;
130		negated = 0;
131
132		/* Process negated host names, or positive netgroups. */
133		if (host[0] == '-') {
134			negated = 1;
135			host++;
136		} else if (host[0] == '+')
137			host++;
138
139		if (user[0] == '-') {
140			negated = 1;
141			user++;
142		} else if (user[0] == '+')
143			user++;
144
145		/* Check for empty host/user names (particularly '+'). */
146		if (!host[0] || !user[0]) {
147			/* We come here if either was '+' or '-'. */
148			auth_debug_add("Ignoring wild host/user names "
149			    "in %.100s.", filename);
150			continue;
151		}
152		/* Verify that host name matches. */
153		if (host[0] == '@') {
154			if (!innetgr(host + 1, hostname, NULL, NULL) &&
155			    !innetgr(host + 1, ipaddr, NULL, NULL))
156				continue;
157		} else if (strcasecmp(host, hostname) &&
158		    strcmp(host, ipaddr) != 0)
159			continue;	/* Different hostname. */
160
161		/* Verify that user name matches. */
162		if (user[0] == '@') {
163			if (!innetgr(user + 1, NULL, client_user, NULL))
164				continue;
165		} else if (strcmp(user, client_user) != 0)
166			continue;	/* Different username. */
167
168		/* Found the user and host. */
169		fclose(f);
170
171		/* If the entry was negated, deny access. */
172		if (negated) {
173			auth_debug_add("Matched negative entry in %.100s.",
174			    filename);
175			return 0;
176		}
177		/* Accept authentication. */
178		return 1;
179	}
180
181	/* Authentication using this file denied. */
182	fclose(f);
183	return 0;
184}
185
186/*
187 * Tries to authenticate the user using the .shosts or .rhosts file. Returns
188 * true if authentication succeeds.  If ignore_rhosts is true, only
189 * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
190 */
191int
192auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
193    const char *ipaddr)
194{
195	char *path = NULL;
196	struct stat st;
197	static const char * const rhosts_files[] = {".shosts", ".rhosts", NULL};
198	u_int rhosts_file_index;
199	int r;
200
201	debug2_f("clientuser %s hostname %s ipaddr %s",
202	    client_user, hostname, ipaddr);
203
204	/* Switch to the user's uid. */
205	temporarily_use_uid(pw);
206	/*
207	 * Quick check: if the user has no .shosts or .rhosts files and
208	 * no system hosts.equiv/shosts.equiv files exist then return
209	 * failure immediately without doing costly lookups from name
210	 * servers.
211	 */
212	for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
213	    rhosts_file_index++) {
214		/* Check users .rhosts or .shosts. */
215		xasprintf(&path, "%s/%s",
216		    pw->pw_dir, rhosts_files[rhosts_file_index]);
217		r = stat(path, &st);
218		free(path);
219		if (r >= 0)
220			break;
221	}
222	/* Switch back to privileged uid. */
223	restore_uid();
224
225	/*
226	 * Deny if The user has no .shosts or .rhosts file and there
227	 * are no system-wide files.
228	 */
229	if (!rhosts_files[rhosts_file_index] &&
230	    stat(_PATH_RHOSTS_EQUIV, &st) == -1 &&
231	    stat(_PATH_SSH_HOSTS_EQUIV, &st) == -1) {
232		debug3_f("no hosts access files exist");
233		return 0;
234	}
235
236	/*
237	 * If not logging in as superuser, try /etc/hosts.equiv and
238	 * shosts.equiv.
239	 */
240	if (pw->pw_uid == 0)
241		debug3_f("root user, ignoring system hosts files");
242	else {
243		if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr,
244		    client_user, pw->pw_name)) {
245			auth_debug_add("Accepted for %.100s [%.100s] by "
246			    "/etc/hosts.equiv.", hostname, ipaddr);
247			return 1;
248		}
249		if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr,
250		    client_user, pw->pw_name)) {
251			auth_debug_add("Accepted for %.100s [%.100s] by "
252			    "%.100s.", hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV);
253			return 1;
254		}
255	}
256
257	/*
258	 * Check that the home directory is owned by root or the user, and is
259	 * not group or world writable.
260	 */
261	if (stat(pw->pw_dir, &st) == -1) {
262		logit("Rhosts authentication refused for %.100s: "
263		    "no home directory %.200s", pw->pw_name, pw->pw_dir);
264		auth_debug_add("Rhosts authentication refused for %.100s: "
265		    "no home directory %.200s", pw->pw_name, pw->pw_dir);
266		return 0;
267	}
268	if (options.strict_modes &&
269	    ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
270	    (st.st_mode & 022) != 0)) {
271		logit("Rhosts authentication refused for %.100s: "
272		    "bad ownership or modes for home directory.", pw->pw_name);
273		auth_debug_add("Rhosts authentication refused for %.100s: "
274		    "bad ownership or modes for home directory.", pw->pw_name);
275		return 0;
276	}
277	/* Temporarily use the user's uid. */
278	temporarily_use_uid(pw);
279
280	/* Check all .rhosts files (currently .shosts and .rhosts). */
281	for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
282	    rhosts_file_index++) {
283		/* Check users .rhosts or .shosts. */
284		xasprintf(&path, "%s/%s",
285		    pw->pw_dir, rhosts_files[rhosts_file_index]);
286		if (stat(path, &st) == -1) {
287			debug3_f("stat %s: %s", path, strerror(errno));
288			free(path);
289			continue;
290		}
291
292		/*
293		 * Make sure that the file is either owned by the user or by
294		 * root, and make sure it is not writable by anyone but the
295		 * owner.  This is to help avoid novices accidentally
296		 * allowing access to their account by anyone.
297		 */
298		if (options.strict_modes &&
299		    ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
300		    (st.st_mode & 022) != 0)) {
301			logit("Rhosts authentication refused for %.100s: "
302			    "bad modes for %.200s", pw->pw_name, path);
303			auth_debug_add("Bad file modes for %.200s", path);
304			free(path);
305			continue;
306		}
307		/*
308		 * Check if we have been configured to ignore .rhosts
309		 * and .shosts files.
310		 */
311		if (options.ignore_rhosts == IGNORE_RHOSTS_YES ||
312		    (options.ignore_rhosts == IGNORE_RHOSTS_SHOSTS &&
313		    strcmp(rhosts_files[rhosts_file_index], ".shosts") != 0)) {
314			auth_debug_add("Server has been configured to "
315			    "ignore %.100s.", rhosts_files[rhosts_file_index]);
316			free(path);
317			continue;
318		}
319		/* Check if authentication is permitted by the file. */
320		if (check_rhosts_file(path, hostname, ipaddr,
321		    client_user, pw->pw_name)) {
322			auth_debug_add("Accepted by %.100s.",
323			    rhosts_files[rhosts_file_index]);
324			/* Restore the privileged uid. */
325			restore_uid();
326			auth_debug_add("Accepted host %s ip %s client_user "
327			    "%s server_user %s", hostname, ipaddr,
328			    client_user, pw->pw_name);
329			free(path);
330			return 1;
331		}
332		free(path);
333	}
334
335	/* Restore the privileged uid. */
336	restore_uid();
337	return 0;
338}
339