release/src/router/busybox/loginutils/su.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * Mini su implementation for busybox
   4  *
   5  * Licensed under GPLv2 or later, see file LICENSE in this source tree.
   6  */
   7
   8 #include "libbb.h"
   9 #include <syslog.h>
  10
  11 #if ENABLE_FEATURE_SU_CHECKS_SHELLS
  12 /* Return 1 if SHELL is a restricted shell (one not returned by
  13  * getusershell), else 0, meaning it is a standard shell.  */
  14 static int restricted_shell(const char *shell)
  15 {
  16         char *line;
  17         int result = 1;
  18
  19         /*setusershell(); - getusershell does it itself*/
  20         while ((line = getusershell()) != NULL) {
  21                 if (/* *line != '#' && */ strcmp(line, shell) == 0) {
  22                         result = 0;
  23                         break;
  24                 }
  25         }
  26         if (ENABLE_FEATURE_CLEAN_UP)
  27                 endusershell();
  28         return result;
  29 }
  30 #endif
  31
  32 #define SU_OPT_mp (3)
  33 #define SU_OPT_l  (4)
  34
  35 int su_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  36 int su_main(int argc UNUSED_PARAM, char **argv)
  37 {
  38         unsigned flags;
  39         char *opt_shell = NULL;
  40         char *opt_command = NULL;
  41         const char *opt_username = "root";
  42         struct passwd *pw;
  43         uid_t cur_uid = getuid();
  44         const char *tty;
  45         char user_buf[64];
  46         const char *old_user;
  47
  48         flags = getopt32(argv, "mplc:s:", &opt_command, &opt_shell);
  49         //argc -= optind;
  50         argv += optind;
  51
  52         if (argv[0] && LONE_DASH(argv[0])) {
  53                 flags |= SU_OPT_l;
  54                 argv++;
  55         }
  56
  57         /* get user if specified */
  58         if (argv[0]) {
  59                 opt_username = argv[0];
  60                 argv++;
  61         }
  62
  63         if (ENABLE_FEATURE_SU_SYSLOG) {
  64                 /* The utmp entry (via getlogin) is probably the best way to
  65                  * identify the user, especially if someone su's from a su-shell.
  66                  * But getlogin can fail -- usually due to lack of utmp entry.
  67                  * in this case resort to getpwuid.  */
  68 #if ENABLE_FEATURE_UTMP
  69                 old_user = user_buf;
  70                 if (getlogin_r(user_buf, sizeof(user_buf)) != 0)
  71 #endif
  72                 {
  73                         pw = getpwuid(cur_uid);
  74                         old_user = pw ? xstrdup(pw->pw_name) : "";
  75                 }
  76                 tty = xmalloc_ttyname(2);
  77                 if (!tty) {
  78                         tty = "none";
  79                 }
  80                 openlog(applet_name, 0, LOG_AUTH);
  81         }
  82
  83         pw = xgetpwnam(opt_username);
  84
  85         if (cur_uid == 0 || correct_password(pw)) {
  86                 if (ENABLE_FEATURE_SU_SYSLOG)
  87                         syslog(LOG_NOTICE, "%c %s %s:%s",
  88                                 '+', tty, old_user, opt_username);
  89         } else {
  90                 if (ENABLE_FEATURE_SU_SYSLOG)
  91                         syslog(LOG_NOTICE, "%c %s %s:%s",
  92                                 '-', tty, old_user, opt_username);
  93                 bb_error_msg_and_die("incorrect password");
  94         }
  95
  96         if (ENABLE_FEATURE_CLEAN_UP && ENABLE_FEATURE_SU_SYSLOG) {
  97                 closelog();
  98         }
  99
 100         if (!opt_shell && (flags & SU_OPT_mp)) {
 101                 /* -s SHELL is not given, but "preserve env" opt is */
 102                 opt_shell = getenv("SHELL");
 103         }
 104
 105         /* Make sure pw->pw_shell is non-NULL.  It may be NULL when NEW_USER
 106          * is a username that is retrieved via NIS (YP), that doesn't have
 107          * a default shell listed.  */
 108         if (!pw->pw_shell || !pw->pw_shell[0])
 109                 pw->pw_shell = (char *)DEFAULT_SHELL;
 110
 111 #if ENABLE_FEATURE_SU_CHECKS_SHELLS
 112         if (opt_shell && cur_uid != 0 && restricted_shell(pw->pw_shell)) {
 113                 /* The user being su'd to has a nonstandard shell, and so is
 114                  * probably a uucp account or has restricted access.  Don't
 115                  * compromise the account by allowing access with a standard
 116                  * shell.  */
 117                 bb_error_msg("using restricted shell");
 118                 opt_shell = NULL;
 119         }
 120         /* else: user can run whatever he wants via "su -s PROG USER".
 121          * This is safe since PROG is run under user's uid/gid. */
 122 #endif
 123         if (!opt_shell)
 124                 opt_shell = pw->pw_shell;
 125
 126         change_identity(pw);
 127         setup_environment(opt_shell,
 128                         ((flags & SU_OPT_l) / SU_OPT_l * SETUP_ENV_CLEARENV)
 129                         + (!(flags & SU_OPT_mp) * SETUP_ENV_CHANGEENV),
 130                         pw);
 131         IF_SELINUX(set_current_security_context(NULL);)
 132
 133         /* Never returns */
 134         run_shell(opt_shell, flags & SU_OPT_l, opt_command, (const char**)argv);
 135
 136         /* return EXIT_FAILURE; - not reached */
 137 }