/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1988, 1993
 *      The Regents of the University of California.  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.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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/types.h>
#include <sys/procctl.h>

#include <ctype.h>
#include <err.h>
#include <errno.h>
#include <grp.h>
#include <limits.h>
#include <paths.h>
#include <pwd.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

static void usage(void) __dead2;

static gid_t
resolve_group(const char *group)
{
        char *endp;
        struct group *gp;
        unsigned long gid;

        gp = getgrnam(group);
        if (gp != NULL)
                return (gp->gr_gid);

        /*
         * Numeric IDs don't need a trip through the database to check them,
         * POSIX seems to think we should generally accept a numeric ID as long
         * as it's within the valid range.
         */
        errno = 0;
        gid = strtoul(group, &endp, 0);
        if (errno == 0 && *endp == '\0' && gid <= GID_MAX)
                return (gid);

        errx(1, "no such group '%s'", group);
}

static uid_t
resolve_user(const char *user)
{
        char *endp;
        struct passwd *pw;
        unsigned long uid;

        pw = getpwnam(user);
        if (pw != NULL)
                return (pw->pw_uid);

        errno = 0;
        uid = strtoul(user, &endp, 0);
        if (errno == 0 && *endp == '\0' && uid <= UID_MAX)
                return (uid);

        errx(1, "no such user '%s'", user);
}

int
main(int argc, char *argv[])
{
        const char      *group, *p, *shell, *user;
        char            *grouplist;
        long            ngroups_max;
        gid_t           gid, *gidlist;
        uid_t           uid;
        int             arg, ch, error, gids;
        bool            nonprivileged;

        gid = 0;
        uid = 0;
        gids = 0;
        user = group = grouplist = NULL;
        gidlist = NULL;
        nonprivileged = false;
        while ((ch = getopt(argc, argv, "G:g:u:n")) != -1) {
                switch(ch) {
                case 'u':
                        user = optarg;
                        if (*user == '\0')
                                usage();
                        break;
                case 'g':
                        group = optarg;
                        if (*group == '\0')
                                usage();
                        break;
                case 'G':
                        grouplist = optarg;

                        /*
                         * XXX Why not allow us to drop all of our supplementary
                         * groups?
                         */
                        if (*grouplist == '\0')
                                usage();
                        break;
                case 'n':
                        nonprivileged = true;
                        break;
                case '?':
                default:
                        usage();
                }
        }
        argc -= optind;
        argv += optind;

        if (argc < 1)
                usage();

        if (group != NULL)
                gid = resolve_group(group);

        if (grouplist != NULL) {
                ngroups_max = sysconf(_SC_NGROUPS_MAX);
                if ((gidlist = malloc(sizeof(gid_t) * ngroups_max)) == NULL)
                        err(1, "malloc");
                for (gids = 0; (p = strsep(&grouplist, ",")) != NULL &&
                    gids < ngroups_max; ) {
                        if (*p == '\0')
                                continue;

                        gidlist[gids++] = resolve_group(p);
                }
                if (p != NULL && gids == ngroups_max)
                        errx(1, "too many supplementary groups provided");
        }

        if (user != NULL)
                uid = resolve_user(user);

        if (nonprivileged) {
                arg = PROC_NO_NEW_PRIVS_ENABLE;
                error = procctl(P_PID, getpid(), PROC_NO_NEW_PRIVS_CTL, &arg);
                if (error != 0)
                        err(1, "procctl");
        }

        if (chdir(argv[0]) == -1)
                err(1, "%s", argv[0]);
        if (chroot(".") == -1) {
                if (errno == EPERM && !nonprivileged && geteuid() != 0)
                        errx(1, "unprivileged use requires -n");
                err(1, "%s", argv[0]);
        }

        if (gidlist != NULL && setgroups(gids, gidlist) == -1)
                err(1, "setgroups");
        if (group && setgid(gid) == -1)
                err(1, "setgid");
        if (user && setuid(uid) == -1)
                err(1, "setuid");

        if (argv[1]) {
                execvp(argv[1], &argv[1]);
                err(1, "%s", argv[1]);
        }

        if (!(shell = getenv("SHELL")))
                shell = _PATH_BSHELL;
        execlp(shell, shell, "-i", (char *)NULL);
        err(1, "%s", shell);
        /* NOTREACHED */
}

static void
usage(void)
{
        (void)fprintf(stderr, "usage: chroot [-g group] [-G group,group,...] "
            "[-u user] [-n] newroot [command]\n");
        exit(1);
}