source: MondoRescue/branches/3.3/mindi-busybox/loginutils/sulogin.c

/* vi: set sw=4 ts=4: */
/*
 * Mini sulogin implementation for busybox
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */
//config:config SULOGIN
//config:   bool "sulogin"
//config:   default y
//config:   select FEATURE_SYSLOG
//config:   help
//config:     sulogin is invoked when the system goes into single user
//config:     mode (this is done through an entry in inittab).

//applet:IF_SULOGIN(APPLET(sulogin, BB_DIR_SBIN, BB_SUID_DROP))

//kbuild:lib-$(CONFIG_SULOGIN) += sulogin.o

//usage:#define sulogin_trivial_usage
//usage:       "[-t N] [TTY]"
//usage:#define sulogin_full_usage "\n\n"
//usage:       "Single user login\n"
//usage:     "\n    -t N    Timeout"

#include "libbb.h"
#include <syslog.h>

int sulogin_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int sulogin_main(int argc UNUSED_PARAM, char **argv)
{
    int timeout = 0;
    struct passwd *pwd;
    const char *shell;

    /* Note: sulogin is not a suid app. It is meant to be run by init
     * for single user / emergency mode. init starts it as root.
     * Normal users (potentially malisious ones) can only run it under
     * their UID, therefore no paranoia here is warranted:
     * $LD_LIBRARY_PATH in env, TTY = /dev/sda
     * are no more dangerous here than in e.g. cp applet.
     */

    logmode = LOGMODE_BOTH;
    openlog(applet_name, 0, LOG_AUTH);

    opt_complementary = "t+"; /* -t N */
    getopt32(argv, "t:", &timeout);
    argv += optind;

    if (argv[0]) {
        close(0);
        close(1);
        dup(xopen(argv[0], O_RDWR));
        close(2);
        dup(0);
    }

    pwd = getpwuid(0);
    if (!pwd) {
        bb_error_msg_and_die("no password entry for root");
    }

    while (1) {
        int r;

        r = ask_and_check_password_extended(pwd, timeout,
            "Give root password for system maintenance\n"
            "(or type Control-D for normal startup):"
        );
        if (r < 0) {
            /* ^D, ^C, timeout, or read error */
            bb_error_msg("normal startup");
            return 0;
        }
        if (r > 0) {
            break;
        }
        bb_do_delay(LOGIN_FAIL_DELAY);
        bb_error_msg("Login incorrect");
    }

    bb_error_msg("starting shell for system maintenance");

    IF_SELINUX(renew_current_security_context());

    shell = getenv("SUSHELL");
    if (!shell)
        shell = getenv("sushell");
    if (!shell)
        shell = pwd->pw_shell;

    /* Exec login shell with no additional parameters. Never returns. */
    run_shell(shell, 1, NULL, NULL);
}