su.c

Unix/Linux下转换用户ID的su程序源码

  if (unencrypted == NULL)
    {
      error (0, 0, _("getpass: cannot open /dev/tty"));
      return 0;
    }
  encrypted = crypt (unencrypted, correct);
  memset (unencrypted, 0, strlen (unencrypted));
  return strcmp (encrypted, correct) == 0;
}

/* Update `environ' for the new shell based on PW, with SHELL being
   the value for the SHELL environment variable.  */

static void
modify_environment (const struct passwd *pw, const char *shell)
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{
  char *term;

  if (simulate_login)
    {
      /* Leave TERM unchanged.  Set HOME, SHELL, USER, LOGNAME, PATH.
         Unset all other environment variables.  */
      term = getenv ("TERM");
      environ = (char **) xmalloc (2 * sizeof (char *));
      environ[0] = 0;
      if (term)
        xputenv (concat ("TERM", "=", term));
      xputenv (concat ("HOME", "=", pw->pw_dir));
      xputenv (concat ("SHELL", "=", shell));
      xputenv (concat ("USER", "=", pw->pw_name));
      xputenv (concat ("LOGNAME", "=", pw->pw_name));
      xputenv (concat ("PATH", "=", pw->pw_uid
                       ? DEFAULT_LOGIN_PATH : DEFAULT_ROOT_LOGIN_PATH));
    }
  else
    {
      /* Set HOME, SHELL, and if not becoming a super-user,
         USER and LOGNAME.  */
      if (change_environment)
        {
          xputenv (concat ("HOME", "=", pw->pw_dir));
          xputenv (concat ("SHELL", "=", shell));
          if (pw->pw_uid)
            {
              xputenv (concat ("USER", "=", pw->pw_name));
              xputenv (concat ("LOGNAME", "=", pw->pw_name));
            }
        }
    }
}

/* Become the user and group(s) specified by PW.  */

static void
change_identity (const struct passwd *pw)
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{
#ifdef HAVE_INITGROUPS
  errno = 0;
  if (initgroups (pw->pw_name, pw->pw_gid) == -1)
    error (1, errno, _("cannot set groups"));
  endgrent ();
#endif
  if (setgid (pw->pw_gid))
    error (1, errno, _("cannot set group id"));
  if (setuid (pw->pw_uid))
    error (1, errno, _("cannot set user id"));
}

/* Run SHELL, or DEFAULT_SHELL if SHELL is empty.
   If COMMAND is nonzero, pass it to the shell with the -c option.
   If ADDITIONAL_ARGS is nonzero, pass it to the shell as more
   arguments.  */

static void
run_shell (const char *shell, const char *command, char **additional_args)
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{
  const char **args;
  int argno = 1;

  if (additional_args)
    args = (const char **) xmalloc (sizeof (char *)
                                    * (10 + elements (additional_args)));
  else
    args = (const char **) xmalloc (sizeof (char *) * 10);
  if (simulate_login)
    {
      char *arg0;
      char *shell_basename;

      shell_basename = basename (shell);
      arg0 = xmalloc (strlen (shell_basename) + 2);
      arg0[0] = '-';
      strcpy (arg0 + 1, shell_basename);
      args[0] = arg0;
    }
  else
    args[0] = basename (shell);
  if (fast_startup)
    args[argno++] = "-f";
  if (command)
    {
      args[argno++] = "-c";
      args[argno++] = command;
    }
  if (additional_args)
    for (; *additional_args; ++additional_args)
      args[argno++] = *additional_args;
  args[argno] = NULL;
  execv (shell, (char **) args);
  error (1, errno, _("cannot run %s"), shell);
}

/* 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)
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{
  char *line;

  setusershell ();
  while ((line = getusershell ()) != NULL)
    {
      if (*line != '#' && strcmp (line, shell) == 0)
        {
          endusershell ();
          return 0;
        }
    }
  endusershell ();
  return 1;
}

static void
usage (int status)
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{
  if (status != 0)
    fprintf (stderr, _("Try `%s --help' for more information.\n"),
             program_name);
  else
    {
      printf (_("Usage: %s [OPTION]... [-] [USER [ARG]...]\n"), program_name);
      printf (_("\
Change the effective user id and group id to that of USER.\n\
\n\
  -, -l, --login               make the shell a login shell\n\
  -c, --commmand=COMMAND       pass a single COMMAND to the shell with -c\n\
  -f, --fast                   pass -f to the shell (for csh or tcsh)\n\
  -m, --preserve-environment   do not reset environment variables\n\
  -p                           same as -m\n\
  -s, --shell=SHELL            run SHELL if /etc/shells allows it\n\
      --help                   display this help and exit\n\
      --version                output version information and exit\n\
\n\
A mere - implies -l.   If USER not given, assume root.\n\
"));
      puts (_("\nReport bugs to [e-mail]"));
    }
  exit (status);
}

int
main (int argc, char **argv)
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{
  int optc;
  const char *new_user = DEFAULT_USER;
  char *command = 0;
  char **additional_args = 0;
  char *shell = 0;
  struct passwd *pw;
  struct passwd pw_copy;

  program_name = argv[0];
  setlocale (LC_ALL, "");
  bindtextdomain (PACKAGE, LOCALEDIR);
  textdomain (PACKAGE);

  fast_startup = 0;
  simulate_login = 0;
  change_environment = 1;

  while ((optc = getopt_long (argc, argv, "c:flmps:", longopts, (int *) 0))
         != EOF)
    {
      switch (optc)
        {
        case 0:
          break;

        case 'c':
          command = optarg;
          break;

        case 'f':
          fast_startup = 1;
          break;

        case 'l':
          simulate_login = 1;
          break;

        case 'm':
        case 'p':
          change_environment = 0;
          break;

        case 's':
          shell = optarg;
          break;

        default:
          usage (1);
        }
    }

  if (show_version)
    {
      printf ("su (%s) %s\n", GNU_PACKAGE, VERSION);
      exit (0);
    }

  if (show_help)
    usage (0);

  if (optind < argc && !strcmp (argv[optind], "-"))
    {
      simulate_login = 1;
      ++optind;
    }
  if (optind < argc)
    new_user = argv[optind++];
  if (optind < argc)
    additional_args = argv + optind;

  pw = getpwnam (new_user);
  if (pw == 0)
    error (1, 0, _("user %s does not exist"), new_user);
  endpwent ();

  /* Make a copy of the password information and point pw at the local
     copy instead.  Otherwise, some systems (e.g. Linux) would clobber
     the static data through the getlogin call from log_su.  */
  pw_copy = *pw;
  pw = &pw_copy;
  pw->pw_name = xstrdup (pw->pw_name);
  pw->pw_dir = xstrdup (pw->pw_dir);
  pw->pw_shell = xstrdup (pw->pw_shell);

  if (!correct_password (pw))
    {
#ifdef SYSLOG_FAILURE
      log_su (pw, 0);
#endif
      error (1, 0, _("incorrect password"));
    }
#ifdef SYSLOG_SUCCESS
  else
    {
      log_su (pw, 1);
    }
#endif

  if (pw->pw_shell == 0 || pw->pw_shell[0] == 0)
    pw->pw_shell = (char *) DEFAULT_SHELL;
  if (shell == 0 && change_environment == 0)
    shell = getenv ("SHELL");
  if (shell != 0 && getuid () && 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.  */
      error (0, 0, _("using restricted shell %s"), pw->pw_shell);
      shell = 0;
    }
  if (shell == 0)
    {
      shell = xstrdup (pw->pw_shell);
    }
  modify_environment (pw, shell);

  change_identity (pw);
  if (simulate_login && chdir (pw->pw_dir))
    error (0, errno, _("warning: cannot change directory to %s"), pw->pw_dir);

  run_shell (shell, command, additional_args);
}