source: MondoRescue/branches/3.3/mindi-busybox/loginutils/su.c@ 3803

/* vi: set sw=4 ts=4: */
/*
 * Mini su implementation for busybox
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */
//config:config SU
//config:   bool "su"
//config:   default y
//config:   select FEATURE_SYSLOG
//config:   help
//config:     su is used to become another user during a login session.
//config:     Invoked without a username, su defaults to becoming the super user.
//config:
//config:     Note that Busybox binary must be setuid root for this applet to
//config:     work properly.
//config:
//config:config FEATURE_SU_SYSLOG
//config:   bool "Enable su to write to syslog"
//config:   default y
//config:   depends on SU
//config:
//config:config FEATURE_SU_CHECKS_SHELLS
//config:   bool "Enable su to check user's shell to be listed in /etc/shells"
//config:   depends on SU
//config:   default y

//applet:/* Needs to be run by root or be suid root - needs to change uid and gid: */
//applet:IF_SU(APPLET(su, BB_DIR_BIN, BB_SUID_REQUIRE))

//kbuild:lib-$(CONFIG_SU) += su.o

//usage:#define su_trivial_usage
//usage:       "[OPTIONS] [-] [USER]"
//usage:#define su_full_usage "\n\n"
//usage:       "Run shell under USER (by default, root)\n"
//usage:     "\n    -,-l    Clear environment, run shell as login shell"
//usage:     "\n    -p,-m   Do not set new $HOME, $SHELL, $USER, $LOGNAME"
//usage:     "\n    -c CMD  Command to pass to 'sh -c'"
//usage:     "\n    -s SH   Shell to use instead of user's default"

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

#if ENABLE_FEATURE_SU_CHECKS_SHELLS
/* Return 1 if SHELL is a restricted shell (one not returned by
 * getusershell), else 0, meaning it is a standard shell.  */
static int restricted_shell(const char *shell)
{
    char *line;
    int result = 1;

    /*setusershell(); - getusershell does it itself*/
    while ((line = getusershell()) != NULL) {
        if (/* *line != '#' && */ strcmp(line, shell) == 0) {
            result = 0;
            break;
        }
    }
    if (ENABLE_FEATURE_CLEAN_UP)
        endusershell();
    return result;
}
#endif

#define SU_OPT_mp (3)
#define SU_OPT_l  (4)

int su_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int su_main(int argc UNUSED_PARAM, char **argv)
{
    unsigned flags;
    char *opt_shell = NULL;
    char *opt_command = NULL;
    const char *opt_username = "root";
    struct passwd *pw;
    uid_t cur_uid = getuid();
    const char *tty;
#if ENABLE_FEATURE_UTMP
    char user_buf[64];
#endif
    const char *old_user;

    flags = getopt32(argv, "mplc:s:", &opt_command, &opt_shell);
    //argc -= optind;
    argv += optind;

    if (argv[0] && LONE_DASH(argv[0])) {
        flags |= SU_OPT_l;
        argv++;
    }

    /* get user if specified */
    if (argv[0]) {
        opt_username = argv[0];
        argv++;
    }

    if (ENABLE_FEATURE_SU_SYSLOG) {
        /* The utmp entry (via getlogin) is probably the best way to
         * identify the user, especially if someone su's from a su-shell.
         * But getlogin can fail -- usually due to lack of utmp entry.
         * in this case resort to getpwuid.  */
#if ENABLE_FEATURE_UTMP
        old_user = user_buf;
        if (getlogin_r(user_buf, sizeof(user_buf)) != 0)
#endif
        {
            pw = getpwuid(cur_uid);
            old_user = pw ? xstrdup(pw->pw_name) : "";
        }
        tty = xmalloc_ttyname(2);
        if (!tty) {
            tty = "none";
        }
        openlog(applet_name, 0, LOG_AUTH);
    }

    pw = xgetpwnam(opt_username);

    if (cur_uid == 0 || ask_and_check_password(pw) > 0) {
        if (ENABLE_FEATURE_SU_SYSLOG)
            syslog(LOG_NOTICE, "%c %s %s:%s",
                '+', tty, old_user, opt_username);
    } else {
        if (ENABLE_FEATURE_SU_SYSLOG)
            syslog(LOG_NOTICE, "%c %s %s:%s",
                '-', tty, old_user, opt_username);
        bb_do_delay(LOGIN_FAIL_DELAY);
        bb_error_msg_and_die("incorrect password");
    }

    if (ENABLE_FEATURE_CLEAN_UP && ENABLE_FEATURE_SU_SYSLOG) {
        closelog();
    }

    if (!opt_shell && (flags & SU_OPT_mp)) {
        /* -s SHELL is not given, but "preserve env" opt is */
        opt_shell = getenv("SHELL");
    }

#if ENABLE_FEATURE_SU_CHECKS_SHELLS
    if (opt_shell && cur_uid != 0 && pw->pw_shell && restricted_shell(pw->pw_shell)) {
        /* The user being su'd to has a nonstandard shell, and so is
         * probably a uucp account or has restricted access.  Don't
         * compromise the account by allowing access with a standard
         * shell.  */
        bb_error_msg("using restricted shell");
        opt_shell = NULL; /* ignore -s PROG */
    }
    /* else: user can run whatever he wants via "su -s PROG USER".
     * This is safe since PROG is run under user's uid/gid. */
#endif
    if (!opt_shell)
        opt_shell = pw->pw_shell;

    change_identity(pw);
    setup_environment(opt_shell,
            ((flags & SU_OPT_l) / SU_OPT_l * SETUP_ENV_CLEARENV)
            + (!(flags & SU_OPT_mp) * SETUP_ENV_CHANGEENV)
            + (!(flags & SU_OPT_l) * SETUP_ENV_NO_CHDIR),
            pw);
    IF_SELINUX(set_current_security_context(NULL);)

    /* Never returns */
    run_shell(opt_shell, flags & SU_OPT_l, opt_command, (const char**)argv);

    /* return EXIT_FAILURE; - not reached */
}