text: /* $OpenBSD: auth-rhosts.c,v 1.44 2010/03/07 11:57:13 dtucker Exp $ */
  /*
   * 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"
  
  /*
   * We support only client side kerberos on Windows.
   */
  
  #ifdef WIN32_FIXME
    #undef GSSAPI
    #undef KRB5
  #endif
  
  #include <sys/types.h>
  #include <sys/stat.h>
  
  #ifdef HAVE_NETGROUP_H
  # include <netgroup.h>
  #endif
  #include <pwd.h>
  #include <stdio.h>
  #include <string.h>
  #include <stdarg.h>
  #include <fcntl.h>
  #include <unistd.h>
  
  #include "packet.h"
  #include "buffer.h"
  #include "uidswap.h"
  #include "pathnames.h"
  #include "log.h"
  #include "servconf.h"
  #include "canohost.h"
  #include "key.h"
  #include "hostfile.h"
  #include "auth.h"
  #include "misc.h"
  
  /* import */
  extern ServerOptions options;
  extern int use_privsep;
  
  /*
   * 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.
   */
  
  static int
  check_rhosts_file(const char *filename, const char *hostname,
  		  const char *ipaddr, const char *client_user,
  		  const char *server_user)
  {
  #ifndef WIN32_FIXME
  	FILE *f;
  	char buf[1024];	/* Must not be larger than host, user, dummy below. */
  	int fd;
  	struct stat st;
  
  	/* Open the .rhosts file, deny if unreadable */
  	if ((fd = open(filename, O_RDONLY|O_NONBLOCK)) == -1)
  		return 0;
  	if (fstat(fd, &st) == -1) {
  		close(fd);
  		return 0;
  	}
  	if (!S_ISREG(st.st_mode)) {
  		logit("User %s hosts file %s is not a regular file",
  		    server_user, filename);
  		close(fd);
  		return 0;
  	}
  	unset_nonblock(fd);
  	if ((f = fdopen(fd, "r")) == NULL) {
  		close(fd);
  		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, "%1023s %1023s %1023s", hostbuf, userbuf,
  		    dummy)) {
  		case 0:
  			auth_debug_add("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:
  			auth_debug_add("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 '-'. */
  			auth_debug_add("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) {
  			auth_debug_add("Matched negative entry in %.100s.",
  			    filename);
  			return 0;
  		}
  		/* Accept authentication. */
  		return 1;
  	}
  
  	/* Authentication using this file denied. */
  	fclose(f);
  	return 0;
  #else
    return 1;
  #endif
  }
  
  /*
   * 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)
  {
  	const char *hostname, *ipaddr;
  
  	hostname = get_canonical_hostname(options.use_dns);
  	ipaddr = get_remote_ipaddr();
  	return auth_rhosts2(pw, client_user, hostname, ipaddr);
  }
  
  static int
  auth_rhosts2_raw(struct passwd *pw, const char *client_user, const char *hostname,
      const char *ipaddr)
  {
  	char buf[1024];
  	struct stat st;
  	static const char *rhosts_files[] = {".shosts", ".rhosts", NULL};
  	u_int rhosts_file_index;
  
  	debug2("auth_rhosts2: clientuser %s hostname %s ipaddr %s",
  	    client_user, hostname, ipaddr);
  
  	/* 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;
  
  	/* 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)) {
  			auth_debug_add("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)) {
  			auth_debug_add("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) {
  		logit("Rhosts authentication refused for %.100s: "
  		    "no home directory %.200s", pw->pw_name, pw->pw_dir);
  		auth_debug_add("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)) {
  		logit("Rhosts authentication refused for %.100s: "
  		    "bad ownership or modes for home directory.", pw->pw_name);
  		auth_debug_add("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)) {
  			logit("Rhosts authentication refused for %.100s: bad modes for %.200s",
  			    pw->pw_name, buf);
  			auth_debug_add("Bad file modes for %.200s", buf);
  			continue;
  		}
  		/* Check if we have been configured to ignore .rhosts and .shosts files. */
  		if (options.ignore_rhosts) {
  			auth_debug_add("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)) {
  			auth_debug_add("Accepted by %.100s.",
  			    rhosts_files[rhosts_file_index]);
  			/* Restore the privileged uid. */
  			restore_uid();
  			auth_debug_add("Accepted host %s ip %s client_user %s server_user %s",
  				hostname, ipaddr, client_user, pw->pw_name);
  			return 1;
  		}
  	}
  
  	/* Restore the privileged uid. */
  	restore_uid();
  	return 0;
  }
  
  int
  auth_rhosts2(struct passwd *pw, const char *client_user, const char *hostname,
      const char *ipaddr)
  {
         return auth_rhosts2_raw(pw, client_user, hostname, ipaddr);
  }
  