/* $OpenBSD: auth-rhosts.c,v 1.58 2024/05/17 00:30:23 djm 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 <sys/types.h>
#include <sys/stat.h>

#include <errno.h>
#include <fcntl.h>
#include <netgroup.h>
#include <pwd.h>
#include <stdio.h>
#include <string.h>
#include <stdarg.h>
#include <stdlib.h>
#include <unistd.h>

#include "packet.h"
#include "uidswap.h"
#include "pathnames.h"
#include "log.h"
#include "misc.h"
#include "xmalloc.h"
#include "sshbuf.h"
#include "sshkey.h"
#include "servconf.h"
#include "canohost.h"
#include "hostfile.h"
#include "auth.h"

/* import */
extern ServerOptions options;

/*
 * 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 *path = NULL;
        struct stat st;
        static const char * const rhosts_files[] = {".shosts", ".rhosts", NULL};
        u_int rhosts_file_index;
        int r;

        debug2_f("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. */
                xasprintf(&path, "%s/%s",
                    pw->pw_dir, rhosts_files[rhosts_file_index]);
                r = stat(path, &st);
                free(path);
                if (r >= 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) == -1 &&
            stat(_PATH_SSH_HOSTS_EQUIV, &st) == -1) {
                debug3_f("no hosts access files exist");
                return 0;
        }

        /*
         * If not logging in as superuser, try /etc/hosts.equiv and
         * shosts.equiv.
         */
        if (pw->pw_uid == 0)
                debug3_f("root user, ignoring system hosts files");
        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) == -1) {
                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. */
                xasprintf(&path, "%s/%s",
                    pw->pw_dir, rhosts_files[rhosts_file_index]);
                if (stat(path, &st) == -1) {
                        debug3_f("stat %s: %s", path, strerror(errno));
                        free(path);
                        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, path);
                        auth_debug_add("Bad file modes for %.200s", path);
                        free(path);
                        continue;
                }
                /*
                 * Check if we have been configured to ignore .rhosts
                 * and .shosts files.
                 */
                if (options.ignore_rhosts == IGNORE_RHOSTS_YES ||
                    (options.ignore_rhosts == IGNORE_RHOSTS_SHOSTS &&
                    strcmp(rhosts_files[rhosts_file_index], ".shosts") != 0)) {
                        auth_debug_add("Server has been configured to "
                            "ignore %.100s.", rhosts_files[rhosts_file_index]);
                        free(path);
                        continue;
                }
                /* Check if authentication is permitted by the file. */
                if (check_rhosts_file(path, 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);
                        free(path);
                        return 1;
                }
                free(path);
        }

        /* Restore the privileged uid. */
        restore_uid();
        return 0;
}