/*-
 * Copyright (c) 2002 Networks Associates Technologies, Inc.
 * All rights reserved.
 *
 * This software was developed for the FreeBSD Project by ThinkSec AS and
 * NAI Labs, the Security Research Division of Network Associates, Inc.
 * under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
 * DARPA CHATS research program.
 *
 * 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.
 * 3. The name of the author may not be used to endorse or promote
 *    products derived from this software without specific prior written
 *    permission.
 *
 * 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.
 *
 * $FreeBSD: doc/en_US.ISO8859-1/articles/pam/su.c,v 1.2 2002/01/24 09:48:49 des Exp $
 */

#include <sys/param.h>
#include <sys/wait.h>

#include <err.h>
#include <stdio.h>
#include <syslog.h>
#include <unistd.h>

#include <security/pam_appl.h>
#include <security/pam_misc.h>

static pam_handle_t *pamh;
static struct pam_conv pamc;

static void
usage(void)
{
        fprintf(stderr, "Usage: su [login [args]]\n");
        exit(1);
}

static int
check(char *func, int pam_err)
{
        if (pam_err == PAM_SUCCESS || pam_err == PAM_NEW_AUTHTOK_REQD)
                return pam_err;
        openlog("su", LOG_CONS, LOG_AUTH);
        syslog(LOG_ERR, "%s(): %s", func, pam_strerror(pamh, pam_err));
        errx(1, "Sorry.");
}

int
main(int argc, char *argv[])
{
        char hostname[MAXHOSTNAMELEN];
        const char *user, *tty;
        int o, status;
        pid_t pid;

        while ((o = getopt(argc, argv, "h")) != -1)
                switch (o) {
                case 'h':
                default:
                        usage();
                }

        argc -= optind;
        argv += optind;

        if (argc > 0)
                user = *argv;
        else
                user = "root";

        /* initialize PAM */
        pamc.conv = &misc_conv;
        pam_start("su", user, &pamc, &pamh);

        /* set some items */
        gethostname(hostname, sizeof hostname);
        check("pam_set_item", pam_set_item(pamh, PAM_RHOST, hostname));
        user = getlogin();
        check("pam_set_item", pam_set_item(pamh, PAM_RUSER, user));
        tty = ttyname(STDERR_FILENO);
        check("pam_set_item", pam_set_item(pamh, PAM_TTY, tty));

        /* authenticate the applicant */
        check("pam_authenticate", pam_authenticate(pamh, 0));
        if (check("pam_acct_mgmt", pam_acct_mgmt(pamh, 0)) ==
            PAM_NEW_AUTHTOK_REQD)
                check("pam_chauthtok",
                    pam_chauthtok(pamh, PAM_CHANGE_EXPIRED_AUTHTOK));
        
        /* establish the requested credentials */
        check("pam_setcred", pam_setcred(pamh, PAM_ESTABLISH_CRED));
        
        /* authentication succeeded; open a session */
        check("pam_open_session", pam_open_session(pamh, 0));

        switch ((pid = fork())) {
        case -1:
                err(1, "fork()");
        case 0:
                /* child: start a shell */
                *argv = "/bin/sh";
                execvp(*argv, argv);
                err(1, "execvp()");
        default:
                /* parent: wait for child to exit */
                waitpid(pid, &status, 0);
                if (WIFEXITED(status))
                        status = WEXITSTATUS(status);
                else
                        status = 1;
        }

        /* close the session and release PAM resources */
        check("pam_close_session", pam_close_session(pamh, 0));
        check("pam_setcred", pam_setcred(pamh, PAM_DELETE_CRED));
        check("pam_end", pam_end(pamh, 0));

        exit(status);
}