/* $OpenBSD: doas.c,v 1.4 2019/10/21 03:14:53 tedu Exp $ */
/*
 * Copyright (c) 2015 Ted Unangst <tedu@openbsd.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/types.h>
#include <sys/stat.h>

#include <limits.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <err.h>
#include <unistd.h>
#include <pwd.h>
#include <grp.h>
#include <syslog.h>
#include <errno.h>

static void __dead
usage(void)
{
        fprintf(stderr, "usage: doas [-u user] command [args]\n");
        exit(1);
}

static int
parseuid(const char *s, uid_t *uid)
{
        struct passwd *pw;
        const char *errstr;

        if ((pw = getpwnam(s)) != NULL) {
                *uid = pw->pw_uid;
                if (*uid == UID_MAX)
                        return -1;
                return 0;
        }
        *uid = strtonum(s, 0, UID_MAX - 1, &errstr);
        if (errstr)
                return -1;
        return 0;
}

int
main(int argc, char **argv)
{
        const char *cmd;
        struct passwd *pw;
        uid_t uid;
        uid_t target = 0;
        gid_t groups[1];
        int ch;

        setprogname("doas");

        closefrom(STDERR_FILENO + 1);

        uid = getuid();
        if (uid != 0)
                errc(1, EPERM, "root only");

        while ((ch = getopt(argc, argv, "u:")) != -1) {
                switch (ch) {
                case 'u':
                        if (parseuid(optarg, &target) != 0)
                                errx(1, "unknown user");
                        break;
                default:
                        usage();
                        break;
                }
        }
        argv += optind;
        argc -= optind;

        if (!argc)
                usage();

        cmd = argv[0];

        pw = getpwuid(target);
        if (!pw)
                errx(1, "no passwd entry for target");
        groups[0] = pw->pw_gid;

        if (setgroups(1, groups) ||
            setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) ||
            setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid))
                err(1, "failed to change user");

        execvp(cmd, argv);
        if (errno == ENOENT)
                errx(1, "%s: command not found", cmd);
        err(1, "%s", cmd);
}