auth-rhosts.c - security/openssh-library - Rivoreo Source Code Repositories

 /*
  * 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 1.22 2001/04/06 21:00:06 markus Exp $");

 #include "packet.h"
 #include "xmalloc.h"
 #include "uidswap.h"
 #include "pathnames.h"
 #include "log.h"
 #include "servconf.h"
 #include "canohost.h"
 #include "auth.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);
 	/*
 	 * 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(_PATH_RHOSTS_EQUIV, &st) < 0 &&
 	    stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0)
 		return 0;

 	hostname = get_canonical_hostname(options.reverse_mapping_check);
 	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(_PATH_RHOSTS_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(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr, client_user,
 				      pw->pw_name)) {
 			packet_send_debug("Accepted for %.100s [%.100s] by %.100s.",
 				      hostname, ipaddr, _PATH_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);

 	/* 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;
 }
	/*
	* 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 1.22 2001/04/06 21:00:06 markus Exp $");

	#include "packet.h"
	#include "xmalloc.h"
	#include "uidswap.h"
	#include "pathnames.h"
	#include "log.h"
	#include "servconf.h"
	#include "canohost.h"
	#include "auth.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);
	/*
	* 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(_PATH_RHOSTS_EQUIV, &st) < 0 &&
	stat(_PATH_SSH_HOSTS_EQUIV, &st) < 0)
	return 0;

	hostname = get_canonical_hostname(options.reverse_mapping_check);
	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(_PATH_RHOSTS_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(_PATH_SSH_HOSTS_EQUIV, hostname, ipaddr, client_user,
	pw->pw_name)) {
	packet_send_debug("Accepted for %.100s [%.100s] by %.100s.",
	hostname, ipaddr, _PATH_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);

	/* 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;
	}