loginutils/sulogin.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * Mini sulogin implementation for busybox
   4  *
   5  * Licensed under GPLv2 or later, see file LICENSE in this source tree.
   6  */
   7 //config:config SULOGIN
   8 //config:       bool "sulogin (18 kb)"
   9 //config:       default y
  10 //config:       select FEATURE_SYSLOG
  11 //config:       help
  12 //config:       sulogin is invoked when the system goes into single user
  13 //config:       mode (this is done through an entry in inittab).
  14
  15 //applet:IF_SULOGIN(APPLET_NOEXEC(sulogin, sulogin, BB_DIR_SBIN, BB_SUID_DROP, sulogin))
  16
  17 //kbuild:lib-$(CONFIG_SULOGIN) += sulogin.o
  18
  19 //usage:#define sulogin_trivial_usage
  20 //usage:       "[-t N] [TTY]"
  21 //usage:#define sulogin_full_usage "\n\n"
  22 //usage:       "Single user login\n"
  23 //usage:     "\n        -p      Start a login shell"
  24 //usage:     "\n        -t SEC  Timeout"
  25
  26 #include "libbb.h"
  27 #include <syslog.h>
  28
  29 int sulogin_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  30 int sulogin_main(int argc UNUSED_PARAM, char **argv)
  31 {
  32         int tsid;
  33         int timeout = 0;
  34         unsigned opts;
  35         struct passwd *pwd;
  36         const char *shell;
  37
  38         /* Note: sulogin is not a suid app. It is meant to be run by init
  39          * for single user / emergency mode. init starts it as root.
  40          * Normal users (potentially malicious ones) can only run it under
  41          * their UID, therefore no paranoia here is warranted:
  42          * $LD_LIBRARY_PATH in env, TTY = /dev/sda
  43          * are no more dangerous here than in e.g. cp applet.
  44          */
  45
  46         logmode = LOGMODE_BOTH;
  47         openlog(applet_name, 0, LOG_AUTH);
  48
  49         opts = getopt32(argv, "pt:+", &timeout);
  50         argv += optind;
  51
  52         if (argv[0]) {
  53                 close(0);
  54                 close(1);
  55                 dup(xopen(argv[0], O_RDWR));
  56                 close(2);
  57                 dup(0);
  58         }
  59
  60         pwd = getpwuid(0);
  61         if (!pwd) {
  62                 bb_simple_error_msg_and_die("no password entry for root");
  63         }
  64
  65         while (1) {
  66                 int r;
  67
  68                 r = ask_and_check_password_extended(pwd, timeout,
  69                         "Give root password for maintenance\n"
  70                         "(or type Ctrl-D to continue): "
  71                 );
  72                 if (r < 0) {
  73                         /* ^D, ^C, timeout, or read error */
  74                         /* util-linux 2.36.1 compat: no message */
  75                         /*bb_simple_info_msg("normal startup");*/
  76                         return 0;
  77                 }
  78                 if (r > 0) {
  79                         break;
  80                 }
  81                 pause_after_failed_login();
  82                 bb_simple_info_msg("Login incorrect");
  83         }
  84
  85         /* util-linux 2.36.1 compat: no message */
  86         /*bb_simple_info_msg("starting shell for system maintenance");*/
  87
  88         IF_SELINUX(renew_current_security_context());
  89
  90         shell = getenv("SUSHELL");
  91         if (!shell)
  92                 shell = getenv("sushell");
  93         if (!shell)
  94                 shell = pwd->pw_shell;
  95
  96         /* util-linux 2.36.1 compat: cd to root's HOME, set a few envvars */
  97         setup_environment(shell, 0
  98                 + SETUP_ENV_CHANGEENV_LOGNAME
  99                 + SETUP_ENV_CHDIR
 100                 , pwd);
 101         // no SETUP_ENV_CLEARENV
 102         // SETUP_ENV_CHANGEENV_LOGNAME - set HOME, SHELL, USER,and LOGNAME
 103         // SETUP_ENV_CHDIR - cd to $HOME
 104
 105         /* util-linux 2.36.1 compat: steal ctty if we don't have it yet
 106          * (yes, util-linux uses force=1)  */
 107         tsid = tcgetsid(STDIN_FILENO);
 108         if (tsid < 0 || getpid() != tsid) {
 109                 if (ioctl(STDIN_FILENO, TIOCSCTTY, /*force:*/ (long)1) != 0) {
 110 //                      bb_perror_msg("TIOCSCTTY1 tsid:%d", tsid);
 111                         if (setsid() > 0) {
 112 //                              bb_error_msg("done setsid()");
 113                                 /* If it still does not work, ignore */
 114                                 if (ioctl(STDIN_FILENO, TIOCSCTTY, /*force:*/ (long)1) != 0) {
 115 //                                      bb_perror_msg("TIOCSCTTY2 tsid:%d", tsid);
 116                                 }
 117                         }
 118                 }
 119         }
 120
 121         /*
 122          * Note: login does this (should we do it too?):
 123          */
 124         /*signal(SIGINT, SIG_DFL);*/
 125
 126         /* Exec shell with no additional parameters. Never returns. */
 127         exec_shell(shell, /* -p? then shell is login:*/(opts & 1), NULL);
 128 }