openssh-portable/auth-rhosts.c

/*
 * 
 * auth-rhosts.c
 * 
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * 
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * 
 * Created: Fri Mar 17 05:12:18 1995 ylo
 * 
 * Rhosts authentication.  This file contains code to check whether to admit
 * the login based on rhosts authentication.  This file also processes
 * /etc/hosts.equiv.
 * 
 */

#include "includes.h"
RCSID("$Id: auth-rhosts.c,v 1.5 1999/11/24 13:26:21 damien 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;

	/* Go through the file, checking every entry. */
	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};
	unsigned int rhosts_file_index;

	/* Quick check: if the user has no .shosts or .rhosts files,
	   return failure immediately without doing costly lookups from
	   name servers. */
	/* Switch to the user's uid. */
	temporarily_use_uid(pw->pw_uid);
	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;

	/* Get the name, address, and port of the remote host.  */
	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 %.100: 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;
}