1/*	$NetBSD: auth-rhosts.c,v 1.16 2023/07/26 17:58:15 christos Exp $	*/
2/* $OpenBSD: auth-rhosts.c,v 1.57 2022/12/09 00:17:40 dtucker Exp $ */
3/*
4 * Author: Tatu Ylonen <ylo@cs.hut.fi>
5 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
6 *                    All rights reserved
7 * Rhosts authentication.  This file contains code to check whether to admit
8 * the login based on rhosts authentication.  This file also processes
9 * /etc/hosts.equiv.
10 *
11 * As far as I am concerned, the code I have written for this software
12 * can be used freely for any purpose.  Any derived versions of this
13 * software must be clearly marked as such, and if the derived work is
14 * incompatible with the protocol description in the RFC file, it must be
15 * called by a name other than "ssh" or "Secure Shell".
16 */
17
18#include "includes.h"
19__RCSID("$NetBSD: auth-rhosts.c,v 1.16 2023/07/26 17:58:15 christos Exp $");
20#include <sys/types.h>
21#include <sys/stat.h>
22
23#include <errno.h>
24#include <fcntl.h>
25#include <netgroup.h>
26#include <pwd.h>
27#include <stdio.h>
28#include <string.h>
29#include <stdarg.h>
30#include <stdlib.h>
31#include <unistd.h>
32
33#include "packet.h"
34#include "uidswap.h"
35#include "pathnames.h"
36#include "log.h"
37#include "misc.h"
38#include "xmalloc.h"
39#include "sshbuf.h"
40#include "sshkey.h"
41#include "servconf.h"
42#include "canohost.h"
43#include "hostfile.h"
44#include "auth.h"
45
46/* import */
47extern ServerOptions options;
48extern int use_privsep;
49
50/*
51 * This function processes an rhosts-style file (.rhosts, .shosts, or
52 * /etc/hosts.equiv).  This returns true if authentication can be granted
53 * based on the file, and returns zero otherwise.
54 */
55
56static int
57check_rhosts_file(const char *filename, const char *hostname,
58		  const char *ipaddr, const char *client_user,
59		  const char *server_user)
60{
61	FILE *f;
62#define RBUFLN 1024
63	char buf[RBUFLN];/* Must not be larger than host, user, dummy below. */
64	int fd;
65	struct stat st;
66
67	/* Open the .rhosts file, deny if unreadable */
68	if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1)
69		return 0;
70	if (fstat(fd, &st) == -1) {
71		close(fd);
72		return 0;
73	}
74	if (!S_ISREG(st.st_mode)) {
75		logit("User %s hosts file %s is not a regular file",
76		    server_user, filename);
77		close(fd);
78		return 0;
79	}
80	unset_nonblock(fd);
81	if ((f = fdopen(fd, "r")) == NULL) {
82		close(fd);
83		return 0;
84	}
85	while (fgets(buf, sizeof(buf), f)) {
86		/* All three must have length >= buf to avoid overflows. */
87		char hostbuf[RBUFLN], userbuf[RBUFLN], dummy[RBUFLN];
88		char *host, *user, *cp;
89		int negated;
90
91		for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
92			;
93		if (*cp == '#' || *cp == '\n' || !*cp)
94			continue;
95
96		/*
97		 * NO_PLUS is supported at least on OSF/1.  We skip it (we
98		 * don't ever support the plus syntax).
99		 */
100		if (strncmp(cp, "NO_PLUS", 7) == 0)
101			continue;
102
103		/*
104		 * This should be safe because each buffer is as big as the
105		 * whole string, and thus cannot be overwritten.
106		 */
107		switch (sscanf(buf, "%1023s %1023s %1023s", hostbuf, userbuf,
108		    dummy)) {
109		case 0:
110			auth_debug_add("Found empty line in %.100s.", filename);
111			continue;
112		case 1:
113			/* Host name only. */
114			strlcpy(userbuf, server_user, sizeof(userbuf));
115			break;
116		case 2:
117			/* Got both host and user name. */
118			break;
119		case 3:
120			auth_debug_add("Found garbage in %.100s.", filename);
121			continue;
122		default:
123			/* Weird... */
124			continue;
125		}
126
127		host = hostbuf;
128		user = userbuf;
129		negated = 0;
130
131		/* Process negated host names, or positive netgroups. */
132		if (host[0] == '-') {
133			negated = 1;
134			host++;
135		} else if (host[0] == '+')
136			host++;
137
138		if (user[0] == '-') {
139			negated = 1;
140			user++;
141		} else if (user[0] == '+')
142			user++;
143
144		/* Check for empty host/user names (particularly '+'). */
145		if (!host[0] || !user[0]) {
146			/* We come here if either was '+' or '-'. */
147			auth_debug_add("Ignoring wild host/user names "
148			    "in %.100s.", filename);
149			continue;
150		}
151		/* Verify that host name matches. */
152		if (host[0] == '@') {
153			if (!innetgr(host + 1, hostname, NULL, NULL) &&
154			    !innetgr(host + 1, ipaddr, NULL, NULL))
155				continue;
156		} else if (strcasecmp(host, hostname) &&
157		    strcmp(host, ipaddr) != 0)
158			continue;	/* Different hostname. */
159
160		/* Verify that user name matches. */
161		if (user[0] == '@') {
162			if (!innetgr(user + 1, NULL, client_user, NULL))
163				continue;
164		} else if (strcmp(user, client_user) != 0)
165			continue;	/* Different username. */
166
167		/* Found the user and host. */
168		fclose(f);
169
170		/* If the entry was negated, deny access. */
171		if (negated) {
172			auth_debug_add("Matched negative entry in %.100s.",
173			    filename);
174			return 0;
175		}
176		/* Accept authentication. */
177		return 1;
178	}
179
180	/* Authentication using this file denied. */
181	fclose(f);
182	return 0;
183}
184
185/*
186 * Tries to authenticate the user using the .shosts or .rhosts file. Returns
187 * true if authentication succeeds.  If ignore_rhosts is true, only
188 * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
189 */
190int
191auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
192    const char *ipaddr)
193{
194	char *path = NULL;
195	struct stat st;
196	static const char * const rhosts_files[] = {".shosts", ".rhosts", NULL};
197	u_int rhosts_file_index;
198	int r;
199
200	debug2_f("clientuser %s hostname %s ipaddr %s",
201	    client_user, hostname, ipaddr);
202
203	/* Switch to the user's uid. */
204	temporarily_use_uid(pw);
205	/*
206	 * Quick check: if the user has no .shosts or .rhosts files and
207	 * no system hosts.equiv/shosts.equiv files exist then return
208	 * failure immediately without doing costly lookups from name
209	 * servers.
210	 */
211	for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
212	    rhosts_file_index++) {
213		/* Check users .rhosts or .shosts. */
214		xasprintf(&path, "%s/%s",
215		    pw->pw_dir, rhosts_files[rhosts_file_index]);
216		r = stat(path, &st);
217		free(path);
218		if (r >= 0)
219			break;
220	}
221	/* Switch back to privileged uid. */
222	restore_uid();
223
224	/*
225	 * Deny if The user has no .shosts or .rhosts file and there
226	 * are no system-wide files.
227	 */
228	if (!rhosts_files[rhosts_file_index] &&
229	    stat(_PATH_RHOSTS_EQUIV, &st) == -1 &&
230	    stat(_PATH_SSH_HOSTS_EQUIV, &st) == -1) {
231		debug3_f("no hosts access files exist");
232		return 0;
233	}
234
235	/*
236	 * If not logging in as superuser, try /etc/hosts.equiv and
237	 * shosts.equiv.
238	 */
239	if (pw->pw_uid == 0)
240		debug3_f("root user, ignoring system hosts files");
241	else {
242		if (check_rhosts_file(_PATH_RHOSTS_EQUIV, hostname, ipaddr,
243		    client_user, pw->pw_name)) {
244			auth_debug_add("Accepted for %.100s [%.100s] by "
245			    "/etc/hosts.equiv.", hostname, ipaddr);
246			return 1;
247		}
248		if (check_rhosts_file(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr,
249		    client_user, pw->pw_name)) {
250			auth_debug_add("Accepted for %.100s [%.100s] by "
251			    "%.100s.", hostname, ipaddr, _PATH_SSH_HOSTS_EQUIV);
252			return 1;
253		}
254	}
255
256	/*
257	 * Check that the home directory is owned by root or the user, and is
258	 * not group or world writable.
259	 */
260	if (stat(pw->pw_dir, &st) == -1) {
261		logit("Rhosts authentication refused for %.100s: "
262		    "no home directory %.200s", pw->pw_name, pw->pw_dir);
263		auth_debug_add("Rhosts authentication refused for %.100s: "
264		    "no home directory %.200s", pw->pw_name, pw->pw_dir);
265		return 0;
266	}
267	if (options.strict_modes &&
268	    ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
269	    (st.st_mode & 022) != 0)) {
270		logit("Rhosts authentication refused for %.100s: "
271		    "bad ownership or modes for home directory.", pw->pw_name);
272		auth_debug_add("Rhosts authentication refused for %.100s: "
273		    "bad ownership or modes for home directory.", pw->pw_name);
274		return 0;
275	}
276	/* Temporarily use the user's uid. */
277	temporarily_use_uid(pw);
278
279	/* Check all .rhosts files (currently .shosts and .rhosts). */
280	for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
281	    rhosts_file_index++) {
282		/* Check users .rhosts or .shosts. */
283		xasprintf(&path, "%s/%s",
284		    pw->pw_dir, rhosts_files[rhosts_file_index]);
285		if (stat(path, &st) == -1) {
286			debug3_f("stat %s: %s", path, strerror(errno));
287			free(path);
288			continue;
289		}
290
291		/*
292		 * Make sure that the file is either owned by the user or by
293		 * root, and make sure it is not writable by anyone but the
294		 * owner.  This is to help avoid novices accidentally
295		 * allowing access to their account by anyone.
296		 */
297		if (options.strict_modes &&
298		    ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
299		    (st.st_mode & 022) != 0)) {
300			logit("Rhosts authentication refused for %.100s: "
301			    "bad modes for %.200s", pw->pw_name, path);
302			auth_debug_add("Bad file modes for %.200s", path);
303			free(path);
304			continue;
305		}
306		/*
307		 * Check if we have been configured to ignore .rhosts
308		 * and .shosts files.
309		 */
310		if (options.ignore_rhosts == IGNORE_RHOSTS_YES ||
311		    (options.ignore_rhosts == IGNORE_RHOSTS_SHOSTS &&
312		    strcmp(rhosts_files[rhosts_file_index], ".shosts") != 0)) {
313			auth_debug_add("Server has been configured to "
314			    "ignore %.100s.", rhosts_files[rhosts_file_index]);
315			free(path);
316			continue;
317		}
318		/* Check if authentication is permitted by the file. */
319		if (check_rhosts_file(path, hostname, ipaddr,
320		    client_user, pw->pw_name)) {
321			auth_debug_add("Accepted by %.100s.",
322			    rhosts_files[rhosts_file_index]);
323			/* Restore the privileged uid. */
324			restore_uid();
325			auth_debug_add("Accepted host %s ip %s client_user "
326			    "%s server_user %s", hostname, ipaddr,
327			    client_user, pw->pw_name);
328			free(path);
329			return 1;
330		}
331		free(path);
332	}
333
334	/* Restore the privileged uid. */
335	restore_uid();
336	return 0;
337}
338