/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2009 Ed Schouten <ed@FreeBSD.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/cdefs.h>
#include <pwd.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <sysexits.h>
#include <ulog.h>

/*
 * This setuid helper utility writes user login records to disk.
 * Unprivileged processes are not capable of writing records to utmpx,
 * but we do want to allow this for pseudo-terminals.  Because a file
 * descriptor to a pseudo-terminal master device can only be obtained by
 * processes using the pseudo-terminal, we expect such a descriptor on
 * stdin.
 *
 * It uses the real user ID of the calling process to determine the
 * username.  It does allow users to log arbitrary hostnames.
 */

static const char *
get_username(void)
{
        const struct passwd *pw;
        const char *login;
        uid_t uid;

        /*
         * Attempt to determine the username corresponding to this login
         * session.  First, validate the results of getlogin() against
         * the password database.  If getlogin() returns invalid data,
         * return an arbitrary username corresponding to this uid.
         */
        uid = getuid();
        if ((login = getlogin()) != NULL && (pw = getpwnam(login)) != NULL &&
            pw->pw_uid == uid)
                return (login);
        if ((pw = getpwuid(uid)) != NULL)
                return (pw->pw_name);
        return (NULL);
}

int
main(int argc, char *argv[])
{
        const char *line, *user, *host;

        /* Device line name. */
        if ((line = ptsname(STDIN_FILENO)) == NULL)
                return (EX_USAGE);

        if ((argc == 2 || argc == 3) && strcmp(argv[1], "login") == 0) {
                /* Username. */
                user = get_username();
                if (user == NULL)
                        return (EX_OSERR);

                /* Hostname. */
                host = argc == 3 ? argv[2] : NULL;

                ulog_login(line, user, host);
                return (EX_OK);
        } else if (argc == 2 && strcmp(argv[1], "logout") == 0) {
                ulog_logout(line);
                return (EX_OK);
        }

        return (EX_USAGE);
}