auth-rhosts.c

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/*
 * 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 1.33 2005/07/17 07:17:54 djm Exp $");

#include "packet.h"
#include "uidswap.h"
#include "pathnames.h"
#include "log.h"
#include "servconf.h"
#include "canohost.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;
        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, "%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_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)
{
        int ret;

        auth_debug_reset();
        ret = auth_rhosts2_raw(pw, client_user, hostname, ipaddr);
        if (!use_privsep)
                auth_debug_send();
        return ret;
}

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