[openssh.git] / auth-rhosts.c

/*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * Rhosts authentication.  This file contains code to check whether to admit
 * the login based on rhosts authentication.  This file also processes
 * /etc/hosts.equiv.
 *
 * As far as I am concerned, the code I have written for this software
 * can be used freely for any purpose.  Any derived versions of this
 * software must be clearly marked as such, and if the derived work is
 * incompatible with the protocol description in the RFC file, it must be
 * called by a name other than "ssh" or "Secure Shell".
 */

#include "includes.h"
RCSID("$OpenBSD: auth-rhosts.c,v 1.17 2000/12/19 23:17:55 markus Exp $");

#include "packet.h"
#include "ssh.h"
#include "xmalloc.h"
#include "uidswap.h"
#include "servconf.h"

/*
 * This function processes an rhosts-style file (.rhosts, .shosts, or
 * /etc/hosts.equiv).  This returns true if authentication can be granted
 * based on the file, and returns zero otherwise.
 */

int
check_rhosts_file(const char *filename, const char *hostname,
		  const char *ipaddr, const char *client_user,
		  const char *server_user)
{
	FILE *f;
	char buf[1024];	/* Must not be larger than host, user, dummy below. */

	/* Open the .rhosts file, deny if unreadable */
	f = fopen(filename, "r");
	if (!f)
		return 0;

	while (fgets(buf, sizeof(buf), f)) {
		/* All three must be at least as big as buf to avoid overflows. */
		char hostbuf[1024], userbuf[1024], dummy[1024], *host, *user, *cp;
		int negated;

		for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
			;
		if (*cp == '#' || *cp == '\n' || !*cp)
			continue;

		/*
		 * NO_PLUS is supported at least on OSF/1.  We skip it (we
		 * don't ever support the plus syntax).
		 */
		if (strncmp(cp, "NO_PLUS", 7) == 0)
			continue;

		/*
		 * This should be safe because each buffer is as big as the
		 * whole string, and thus cannot be overwritten.
		 */
		switch (sscanf(buf, "%s %s %s", hostbuf, userbuf, dummy)) {
		case 0:
			packet_send_debug("Found empty line in %.100s.", filename);
			continue;
		case 1:
			/* Host name only. */
			strlcpy(userbuf, server_user, sizeof(userbuf));
			break;
		case 2:
			/* Got both host and user name. */
			break;
		case 3:
			packet_send_debug("Found garbage in %.100s.", filename);
			continue;
		default:
			/* Weird... */
			continue;
		}

		host = hostbuf;
		user = userbuf;
		negated = 0;

		/* Process negated host names, or positive netgroups. */
		if (host[0] == '-') {
			negated = 1;
			host++;
		} else if (host[0] == '+')
			host++;

		if (user[0] == '-') {
			negated = 1;
			user++;
		} else if (user[0] == '+')
			user++;

		/* Check for empty host/user names (particularly '+'). */
		if (!host[0] || !user[0]) {
			/* We come here if either was '+' or '-'. */
			packet_send_debug("Ignoring wild host/user names in %.100s.",
					  filename);
			continue;
		}
		/* Verify that host name matches. */
		if (host[0] == '@') {
			if (!innetgr(host + 1, hostname, NULL, NULL) &&
			    !innetgr(host + 1, ipaddr, NULL, NULL))
				continue;
		} else if (strcasecmp(host, hostname) && strcmp(host, ipaddr) != 0)
			continue;	/* Different hostname. */

		/* Verify that user name matches. */
		if (user[0] == '@') {
			if (!innetgr(user + 1, NULL, client_user, NULL))
				continue;
		} else if (strcmp(user, client_user) != 0)
			continue;	/* Different username. */

		/* Found the user and host. */
		fclose(f);

		/* If the entry was negated, deny access. */
		if (negated) {
			packet_send_debug("Matched negative entry in %.100s.",
					  filename);
			return 0;
		}
		/* Accept authentication. */
		return 1;
	}

	/* Authentication using this file denied. */
	fclose(f);
	return 0;
}

/*
 * Tries to authenticate the user using the .shosts or .rhosts file. Returns
 * true if authentication succeeds.  If ignore_rhosts is true, only
 * /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
 */

int
auth_rhosts(struct passwd *pw, const char *client_user)
{
	extern ServerOptions options;
	char buf[1024];
	const char *hostname, *ipaddr;
	struct stat st;
	static const char *rhosts_files[] = {".shosts", ".rhosts", NULL};
	u_int rhosts_file_index;

	/* no user given */
	if (pw == NULL)
		return 0;
	/* Switch to the user's uid. */
	temporarily_use_uid(pw->pw_uid);
	/*
	 * Quick check: if the user has no .shosts or .rhosts files, return
	 * failure immediately without doing costly lookups from name
	 * servers.
	 */
	for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
	     rhosts_file_index++) {
		/* Check users .rhosts or .shosts. */
		snprintf(buf, sizeof buf, "%.500s/%.100s",
			 pw->pw_dir, rhosts_files[rhosts_file_index]);
		if (stat(buf, &st) >= 0)
			break;
	}
	/* Switch back to privileged uid. */
	restore_uid();

	/* Deny if The user has no .shosts or .rhosts file and there are no system-wide files. */
	if (!rhosts_files[rhosts_file_index] &&
	    stat("/etc/hosts.equiv", &st) < 0 &&
	    stat(SSH_HOSTS_EQUIV, &st) < 0)
		return 0;

	hostname = get_canonical_hostname();
	ipaddr = get_remote_ipaddr();

	/* If not logging in as superuser, try /etc/hosts.equiv and shosts.equiv. */
	if (pw->pw_uid != 0) {
		if (check_rhosts_file("/etc/hosts.equiv", hostname, ipaddr, client_user,
				      pw->pw_name)) {
			packet_send_debug("Accepted for %.100s [%.100s] by /etc/hosts.equiv.",
					  hostname, ipaddr);
			return 1;
		}
		if (check_rhosts_file(SSH_HOSTS_EQUIV, hostname, ipaddr, client_user,
				      pw->pw_name)) {
			packet_send_debug("Accepted for %.100s [%.100s] by %.100s.",
				      hostname, ipaddr, SSH_HOSTS_EQUIV);
			return 1;
		}
	}
	/*
	 * Check that the home directory is owned by root or the user, and is
	 * not group or world writable.
	 */
	if (stat(pw->pw_dir, &st) < 0) {
		log("Rhosts authentication refused for %.100s: no home directory %.200s",
		    pw->pw_name, pw->pw_dir);
		packet_send_debug("Rhosts authentication refused for %.100s: no home directory %.200s",
				  pw->pw_name, pw->pw_dir);
		return 0;
	}
	if (options.strict_modes &&
	    ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
	     (st.st_mode & 022) != 0)) {
		log("Rhosts authentication refused for %.100s: bad ownership or modes for home directory.",
		    pw->pw_name);
		packet_send_debug("Rhosts authentication refused for %.100s: bad ownership or modes for home directory.",
				  pw->pw_name);
		return 0;
	}
	/* Temporarily use the user's uid. */
	temporarily_use_uid(pw->pw_uid);

	/* Check all .rhosts files (currently .shosts and .rhosts). */
	for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
	     rhosts_file_index++) {
		/* Check users .rhosts or .shosts. */
		snprintf(buf, sizeof buf, "%.500s/%.100s",
			 pw->pw_dir, rhosts_files[rhosts_file_index]);
		if (stat(buf, &st) < 0)
			continue;

		/*
		 * Make sure that the file is either owned by the user or by
		 * root, and make sure it is not writable by anyone but the
		 * owner.  This is to help avoid novices accidentally
		 * allowing access to their account by anyone.
		 */
		if (options.strict_modes &&
		    ((st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
		     (st.st_mode & 022) != 0)) {
			log("Rhosts authentication refused for %.100s: bad modes for %.200s",
			    pw->pw_name, buf);
			packet_send_debug("Bad file modes for %.200s", buf);
			continue;
		}
		/* Check if we have been configured to ignore .rhosts and .shosts files. */
		if (options.ignore_rhosts) {
			packet_send_debug("Server has been configured to ignore %.100s.",
					  rhosts_files[rhosts_file_index]);
			continue;
		}
		/* Check if authentication is permitted by the file. */
		if (check_rhosts_file(buf, hostname, ipaddr, client_user, pw->pw_name)) {
			packet_send_debug("Accepted by %.100s.",
					  rhosts_files[rhosts_file_index]);
			/* Restore the privileged uid. */
			restore_uid();
			return 1;
		}
	}

	/* Restore the privileged uid. */
	restore_uid();
	return 0;
}
Commit	Line	Data
8efc0c15	1	/*
5260325f	2	* Author: Tatu Ylonen <ylo@cs.hut.fi>
5260325f	3	* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5260325f	4	* All rights reserved
5260325f	5	* Rhosts authentication. This file contains code to check whether to admit
	6	* the login based on rhosts authentication. This file also processes
	7	* /etc/hosts.equiv.
6ae2364d	8	*
bcbf86ec	9	* As far as I am concerned, the code I have written for this software
	10	* can be used freely for any purpose. Any derived versions of this
	11	* software must be clearly marked as such, and if the derived work is
	12	* incompatible with the protocol description in the RFC file, it must be
	13	* called by a name other than "ssh" or "Secure Shell".
5260325f	14	*/
8efc0c15	15
8efc0c15	16	#include "includes.h"
1e3b8b07	17	RCSID("$OpenBSD: auth-rhosts.c,v 1.17 2000/12/19 23:17:55 markus Exp $");
8efc0c15	18
	19	#include "packet.h"
	20	#include "ssh.h"
	21	#include "xmalloc.h"
	22	#include "uidswap.h"
6fa724bc	23	#include "servconf.h"
8efc0c15	24
aa3378df	25	/*
	26	* This function processes an rhosts-style file (.rhosts, .shosts, or
	27	* /etc/hosts.equiv). This returns true if authentication can be granted
	28	* based on the file, and returns zero otherwise.
	29	*/
8efc0c15	30
6ae2364d	31	int
5260325f	32	check_rhosts_file(const char filename, const char hostname,
	33	const char ipaddr, const char client_user,
	34	const char *server_user)
8efc0c15	35	{
5260325f	36	FILE *f;
	37	char buf[1024]; /* Must not be larger than host, user, dummy below. */
	38
	39	/* Open the .rhosts file, deny if unreadable */
	40	f = fopen(filename, "r");
	41	if (!f)
	42	return 0;
	43
5260325f	44	while (fgets(buf, sizeof(buf), f)) {
	45	/* All three must be at least as big as buf to avoid overflows. */
	46	char hostbuf[1024], userbuf[1024], dummy[1024], host, user, *cp;
	47	int negated;
	48
	49	for (cp = buf; cp == ' ' \|\| cp == '\t'; cp++)
	50	;
	51	if (cp == '#' \|\| cp == '\n' \|\| !*cp)
	52	continue;
	53
aa3378df	54	/*
	55	* NO_PLUS is supported at least on OSF/1. We skip it (we
	56	* don't ever support the plus syntax).
	57	*/
5260325f	58	if (strncmp(cp, "NO_PLUS", 7) == 0)
	59	continue;
	60
aa3378df	61	/*
	62	* This should be safe because each buffer is as big as the
	63	* whole string, and thus cannot be overwritten.
	64	*/
5260325f	65	switch (sscanf(buf, "%s %s %s", hostbuf, userbuf, dummy)) {
	66	case 0:
	67	packet_send_debug("Found empty line in %.100s.", filename);
	68	continue;
	69	case 1:
	70	/* Host name only. */
	71	strlcpy(userbuf, server_user, sizeof(userbuf));
	72	break;
	73	case 2:
	74	/* Got both host and user name. */
	75	break;
	76	case 3:
	77	packet_send_debug("Found garbage in %.100s.", filename);
	78	continue;
	79	default:
	80	/* Weird... */
	81	continue;
	82	}
	83
	84	host = hostbuf;
	85	user = userbuf;
	86	negated = 0;
	87
	88	/* Process negated host names, or positive netgroups. */
	89	if (host[0] == '-') {
	90	negated = 1;
	91	host++;
	92	} else if (host[0] == '+')
	93	host++;
	94
	95	if (user[0] == '-') {
	96	negated = 1;
	97	user++;
	98	} else if (user[0] == '+')
	99	user++;
	100
	101	/* Check for empty host/user names (particularly '+'). */
	102	if (!host[0] \|\| !user[0]) {
	103	/* We come here if either was '+' or '-'. */
	104	packet_send_debug("Ignoring wild host/user names in %.100s.",
	105	filename);
	106	continue;
	107	}
	108	/* Verify that host name matches. */
	109	if (host[0] == '@') {
	110	if (!innetgr(host + 1, hostname, NULL, NULL) &&
	111	!innetgr(host + 1, ipaddr, NULL, NULL))
	112	continue;
	113	} else if (strcasecmp(host, hostname) && strcmp(host, ipaddr) != 0)
	114	continue; /* Different hostname. */
	115
	116	/* Verify that user name matches. */
	117	if (user[0] == '@') {
	118	if (!innetgr(user + 1, NULL, client_user, NULL))
	119	continue;
	120	} else if (strcmp(user, client_user) != 0)
	121	continue; /* Different username. */
	122
	123	/* Found the user and host. */
	124	fclose(f);
	125
	126	/* If the entry was negated, deny access. */
	127	if (negated) {
	128	packet_send_debug("Matched negative entry in %.100s.",
129	filename);
130	return 0;
131	}
132	/* Accept authentication. */
133	return 1;
8efc0c15	134	}
8efc0c15	135
5260325f	136	/* Authentication using this file denied. */
	137	fclose(f);
	138	return 0;
8efc0c15	139	}
8efc0c15	140
aa3378df	141	/*
	142	* Tries to authenticate the user using the .shosts or .rhosts file. Returns
	143	* true if authentication succeeds. If ignore_rhosts is true, only
	144	* /etc/hosts.equiv will be considered (.rhosts and .shosts are ignored).
	145	*/
8efc0c15	146
6ae2364d	147	int
5260325f	148	auth_rhosts(struct passwd pw, const char client_user)
8efc0c15	149	{
5260325f	150	extern ServerOptions options;
	151	char buf[1024];
	152	const char hostname, ipaddr;
	153	struct stat st;
	154	static const char *rhosts_files[] = {".shosts", ".rhosts", NULL};
1e3b8b07	155	u_int rhosts_file_index;
5260325f	156
94ec8c6b	157	/* no user given */
	158	if (pw == NULL)
	159	return 0;
5260325f	160	/* Switch to the user's uid. */
5260325f	161	temporarily_use_uid(pw->pw_uid);
aa3378df	162	/*
	163	* Quick check: if the user has no .shosts or .rhosts files, return
	164	* failure immediately without doing costly lookups from name
	165	* servers.
	166	*/
5260325f	167	for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
	168	rhosts_file_index++) {
	169	/* Check users .rhosts or .shosts. */
	170	snprintf(buf, sizeof buf, "%.500s/%.100s",
	171	pw->pw_dir, rhosts_files[rhosts_file_index]);
	172	if (stat(buf, &st) >= 0)
	173	break;
8efc0c15	174	}
5260325f	175	/* Switch back to privileged uid. */
	176	restore_uid();
	177
	178	/* Deny if The user has no .shosts or .rhosts file and there are no system-wide files. */
	179	if (!rhosts_files[rhosts_file_index] &&
	180	stat("/etc/hosts.equiv", &st) < 0 &&
	181	stat(SSH_HOSTS_EQUIV, &st) < 0)
	182	return 0;
	183
5260325f	184	hostname = get_canonical_hostname();
	185	ipaddr = get_remote_ipaddr();
	186
	187	/* If not logging in as superuser, try /etc/hosts.equiv and shosts.equiv. */
	188	if (pw->pw_uid != 0) {
	189	if (check_rhosts_file("/etc/hosts.equiv", hostname, ipaddr, client_user,
	190	pw->pw_name)) {
	191	packet_send_debug("Accepted for %.100s [%.100s] by /etc/hosts.equiv.",
	192	hostname, ipaddr);
	193	return 1;
	194	}
	195	if (check_rhosts_file(SSH_HOSTS_EQUIV, hostname, ipaddr, client_user,
	196	pw->pw_name)) {
	197	packet_send_debug("Accepted for %.100s [%.100s] by %.100s.",
	198	hostname, ipaddr, SSH_HOSTS_EQUIV);
	199	return 1;
	200	}
8efc0c15	201	}
aa3378df	202	/*
	203	* Check that the home directory is owned by root or the user, and is
	204	* not group or world writable.
	205	*/
5260325f	206	if (stat(pw->pw_dir, &st) < 0) {
	207	log("Rhosts authentication refused for %.100s: no home directory %.200s",
	208	pw->pw_name, pw->pw_dir);
00e6dd70	209	packet_send_debug("Rhosts authentication refused for %.100s: no home directory %.200s",
5260325f	210	pw->pw_name, pw->pw_dir);
5260325f	211	return 0;
8efc0c15	212	}
5260325f	213	if (options.strict_modes &&
	214	((st.st_uid != 0 && st.st_uid != pw->pw_uid) \|\|
	215	(st.st_mode & 022) != 0)) {
	216	log("Rhosts authentication refused for %.100s: bad ownership or modes for home directory.",
	217	pw->pw_name);
	218	packet_send_debug("Rhosts authentication refused for %.100s: bad ownership or modes for home directory.",
	219	pw->pw_name);
	220	return 0;
8efc0c15	221	}
5260325f	222	/* Temporarily use the user's uid. */
	223	temporarily_use_uid(pw->pw_uid);
	224
	225	/* Check all .rhosts files (currently .shosts and .rhosts). */
	226	for (rhosts_file_index = 0; rhosts_files[rhosts_file_index];
	227	rhosts_file_index++) {
	228	/* Check users .rhosts or .shosts. */
	229	snprintf(buf, sizeof buf, "%.500s/%.100s",
	230	pw->pw_dir, rhosts_files[rhosts_file_index]);
	231	if (stat(buf, &st) < 0)
	232	continue;
	233
aa3378df	234	/*
	235	* Make sure that the file is either owned by the user or by
	236	* root, and make sure it is not writable by anyone but the
	237	* owner. This is to help avoid novices accidentally
	238	* allowing access to their account by anyone.
	239	*/
5260325f	240	if (options.strict_modes &&
	241	((st.st_uid != 0 && st.st_uid != pw->pw_uid) \|\|
	242	(st.st_mode & 022) != 0)) {
	243	log("Rhosts authentication refused for %.100s: bad modes for %.200s",
	244	pw->pw_name, buf);
	245	packet_send_debug("Bad file modes for %.200s", buf);
	246	continue;
	247	}
	248	/* Check if we have been configured to ignore .rhosts and .shosts files. */
	249	if (options.ignore_rhosts) {
	250	packet_send_debug("Server has been configured to ignore %.100s.",
	251	rhosts_files[rhosts_file_index]);
	252	continue;
	253	}
	254	/* Check if authentication is permitted by the file. */
	255	if (check_rhosts_file(buf, hostname, ipaddr, client_user, pw->pw_name)) {
	256	packet_send_debug("Accepted by %.100s.",
	257	rhosts_files[rhosts_file_index]);
	258	/* Restore the privileged uid. */
	259	restore_uid();
	260	return 1;
	261	}
8efc0c15	262	}
8efc0c15	263
5260325f	264	/* Restore the privileged uid. */
	265	restore_uid();
	266	return 0;
8efc0c15	267	}