/* $OpenBSD: auth-rhosts.c,v 1.48 2016/08/13 17:47:41 markus 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"
#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 "uidswap.h"
#include "pathnames.h"
#include "log.h"
#include "misc.h"
#include "buffer.h" /* XXX */
#include "key.h" /* XXX */
#include "servconf.h"
#include "canohost.h"
#include "sshkey.h"
#include "hostfile.h"
#include "auth.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)
{
FILE *f;
#define RBUFLN 1024
char buf[RBUFLN];/* 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 have length >= buf to avoid overflows. */
char hostbuf[RBUFLN], userbuf[RBUFLN], dummy[RBUFLN];
char *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;
}
/*
* 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_rhosts2(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 and
* no system hosts.equiv/shosts.equiv files exist then 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) {
debug3("%s: no hosts access files exist", __func__);
return 0;
}
/*
* If not logging in as superuser, try /etc/hosts.equiv and
* shosts.equiv.
*/
if (pw->pw_uid == 0)
debug3("%s: root user, ignoring system hosts files", __func__);
else {
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;
}
