1/* $OpenBSD: auth-rhosts.c,v 1.58 2024/05/17 00:30:23 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 <sys/types.h>
18#include <sys/stat.h>
19
20#include <errno.h>
21#include <fcntl.h>
22#include <netgroup.h>
23#include <pwd.h>
24#include <stdio.h>
25#include <string.h>
26#include <stdarg.h>
27#include <stdlib.h>
28#include <unistd.h>
29
30#include "packet.h"
31#include "uidswap.h"
32#include "pathnames.h"
33#include "log.h"
34#include "misc.h"
35#include "xmalloc.h"
36#include "sshbuf.h"
37#include "sshkey.h"
38#include "servconf.h"
39#include "canohost.h"
40#include "hostfile.h"
41#include "auth.h"
42
43/* import */
44extern ServerOptions options;
45
46/*
47 * This function processes an rhosts-style file (.rhosts, .shosts, or
48 * /etc/hosts.equiv).  This returns true if authentication can be granted
49 * based on the file, and returns zero otherwise.
50 */
51
52static int
53check_rhosts_file(const char *filename, const char *hostname,
54		  const char *ipaddr, const char *client_user,
55		  const char *server_user)
56{
57	FILE *f;
58#define RBUFLN 1024
59	char buf[RBUFLN];/* Must not be larger than host, user, dummy below. */
60	int fd;
61	struct stat st;
62
63	/* Open the .rhosts file, deny if unreadable */
64	if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1)
65		return 0;
66	if (fstat(fd, &st) == -1) {
67		close(fd);
68		return 0;
69	}
70	if (!S_ISREG(st.st_mode)) {
71		logit("User %s hosts file %s is not a regular file",
72		    server_user, filename);
73		close(fd);
74		return 0;
75	}
76	unset_nonblock(fd);
77	if ((f = fdopen(fd, "r")) == NULL) {
78		close(fd);
79		return 0;
80	}
81	while (fgets(buf, sizeof(buf), f)) {
82		/* All three must have length >= buf to avoid overflows. */
83		char hostbuf[RBUFLN], userbuf[RBUFLN], dummy[RBUFLN];
84		char *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 "
144			    "in %.100s.", 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) &&
153		    strcmp(host, ipaddr) != 0)
154			continue;	/* Different hostname. */
155
156		/* Verify that user name matches. */
157		if (user[0] == '@') {
158			if (!innetgr(user + 1, NULL, client_user, NULL))
159				continue;
160		} else if (strcmp(user, client_user) != 0)
161			continue;	/* Different username. */
162
163		/* Found the user and host. */
164		fclose(f);
165
166		/* If the entry was negated, deny access. */
167		if (negated) {
168			auth_debug_add("Matched negative entry in %.100s.",
169			    filename);
170			return 0;
171		}
172		/* Accept authentication. */
173		return 1;
174	}
175
176	/* Authentication using this file denied. */
177	fclose(f);
178	return 0;
179}
180
181/*
182 * Tries to authenticate the user using the .shosts or .rhosts file. Returns
183 * true if authentication succeeds.  If ignore_rhosts is true, only
184 * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
185 */
186int
187auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
188    const char *ipaddr)
189{
190	char *path = NULL;
191	struct stat st;
192	static const char * const rhosts_files[] = {".shosts", ".rhosts", NULL};
193	u_int rhosts_file_index;
194	int r;
195
196	debug2_f("clientuser %s hostname %s ipaddr %s",
197	    client_user, hostname, ipaddr);
198
199	/* Switch to the user's uid. */
200	temporarily_use_uid(pw);
201	/*
202	 * Quick check: if the user has no .shosts or .rhosts files and
203	 * no system hosts.equiv/shosts.equiv files exist then return
204	 * failure immediately without doing costly lookups from name
205	 * servers.
206	 */
207	for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
208	    rhosts_file_index++) {
209		/* Check users .rhosts or .shosts. */
210		xasprintf(&path, "%s/%s",
211		    pw->pw_dir, rhosts_files[rhosts_file_index]);
212		r = stat(path, &st);
213		free(path);
214		if (r >= 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) == -1 &&
226	    stat(_PATH_SSH_HOSTS_EQUIV, &st) == -1) {
227		debug3_f("no hosts access files exist");
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_f("root user, ignoring system hosts files");
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) == -1) {
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		xasprintf(&path, "%s/%s",
280		    pw->pw_dir, rhosts_files[rhosts_file_index]);
281		if (stat(path, &st) == -1) {
282			debug3_f("stat %s: %s", path, strerror(errno));
283			free(path);
284			continue;
285		}
286
287		/*
288		 * Make sure that the file is either owned by the user or by
289		 * root, and make sure it is not writable by anyone but the
290		 * owner.  This is to help avoid novices accidentally
291		 * allowing access to their account by anyone.
292		 */
293		if (options.strict_modes &&
294		    ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
295		    (st.st_mode & 022) != 0)) {
296			logit("Rhosts authentication refused for %.100s: "
297			    "bad modes for %.200s", pw->pw_name, path);
298			auth_debug_add("Bad file modes for %.200s", path);
299			free(path);
300			continue;
301		}
302		/*
303		 * Check if we have been configured to ignore .rhosts
304		 * and .shosts files.
305		 */
306		if (options.ignore_rhosts == IGNORE_RHOSTS_YES ||
307		    (options.ignore_rhosts == IGNORE_RHOSTS_SHOSTS &&
308		    strcmp(rhosts_files[rhosts_file_index], ".shosts") != 0)) {
309			auth_debug_add("Server has been configured to "
310			    "ignore %.100s.", rhosts_files[rhosts_file_index]);
311			free(path);
312			continue;
313		}
314		/* Check if authentication is permitted by the file. */
315		if (check_rhosts_file(path, hostname, ipaddr,
316		    client_user, pw->pw_name)) {
317			auth_debug_add("Accepted by %.100s.",
318			    rhosts_files[rhosts_file_index]);
319			/* Restore the privileged uid. */
320			restore_uid();
321			auth_debug_add("Accepted host %s ip %s client_user "
322			    "%s server_user %s", hostname, ipaddr,
323			    client_user, pw->pw_name);
324			free(path);
325			return 1;
326		}
327		free(path);
328	}
329
330	/* Restore the privileged uid. */
331	restore_uid();
332	return 0;
333}
334