path: root/src/chroot.c

/* chroot -- run command or shell with special root directory
   Copyright (C) 1995-1997, 1999-2004, 2007-2012 Free Software Foundation, Inc.

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

/* Written by Roland McGrath.  */

#include <config.h>
#include <getopt.h>
#include <stdio.h>
#include <sys/types.h>
#include <grp.h>

#include "system.h"
#include "error.h"
#include "quote.h"
#include "userspec.h"
#include "xstrtol.h"

/* The official name of this program (e.g., no `g' prefix).  */
#define PROGRAM_NAME "chroot"

#define AUTHORS proper_name ("Roland McGrath")

#ifndef MAXGID
# define MAXGID GID_T_MAX
#endif

enum
{
  GROUPS = UCHAR_MAX + 1,
  USERSPEC
};

static struct option const long_opts[] =
{
  {"groups", required_argument, NULL, GROUPS},
  {"userspec", required_argument, NULL, USERSPEC},
  {GETOPT_HELP_OPTION_DECL},
  {GETOPT_VERSION_OPTION_DECL},
  {NULL, 0, NULL, 0}
};

#if ! HAVE_SETGROUPS
/* At least Interix lacks supplemental group support.  Define an
   always-successful replacement to avoid checking for setgroups
   availability everywhere, just to support broken platforms. */
static int
setgroups (size_t size ATTRIBUTE_UNUSED, gid_t const *list ATTRIBUTE_UNUSED)
{
  return 0;
}
#endif

/* Call setgroups to set the supplementary groups to those listed in GROUPS.
   GROUPS is a comma separated list of supplementary groups (names or numbers).
   Parse that list, converting any names to numbers, and call setgroups on the
   resulting numbers.  Upon any failure give a diagnostic and return nonzero.
   Otherwise return zero.  */
static int
set_additional_groups (char const *groups)
{
  GETGROUPS_T *gids = NULL;
  size_t n_gids_allocated = 0;
  size_t n_gids = 0;
  char *buffer = xstrdup (groups);
  char const *tmp;
  int ret = 0;

  for (tmp = strtok (buffer, ","); tmp; tmp = strtok (NULL, ","))
    {
      struct group *g;
      unsigned long int value;

      if (xstrtoul (tmp, NULL, 10, &value, "") == LONGINT_OK && value <= MAXGID)
        g = getgrgid (value);
      else
        {
          g = getgrnam (tmp);
          if (g != NULL)
            value = g->gr_gid;
        }

      if (g == NULL)
        {
          error (0, errno, _("invalid group %s"), quote (tmp));
          ret = -1;
          continue;
        }

      if (n_gids == n_gids_allocated)
        gids = X2NREALLOC (gids, &n_gids_allocated);
      gids[n_gids++] = value;
    }

  if (ret == 0 && n_gids == 0)
    {
      error (0, 0, _("invalid group list %s"), quote (groups));
      ret = -1;
    }

  if (ret == 0)
    {
      ret = setgroups (n_gids, gids);
      if (ret)
        error (0, errno, _("failed to set additional groups"));
    }

  free (buffer);
  free (gids);
  return ret;
}

void
usage (int status)
{
  if (status != EXIT_SUCCESS)
    emit_try_help ();
  else
    {
      printf (_("\
Usage: %s [OPTION] NEWROOT [COMMAND [ARG]...]\n\
  or:  %s OPTION\n\
"), program_name, program_name);

      fputs (_("\
Run COMMAND with root directory set to NEWROOT.\n\
\n\
"), stdout);

      fputs (_("\
  --userspec=USER:GROUP  specify user and group (ID or name) to use\n\
  --groups=G_LIST        specify supplementary groups as g1,g2,..,gN\n\
"), stdout);

      fputs (HELP_OPTION_DESCRIPTION, stdout);
      fputs (VERSION_OPTION_DESCRIPTION, stdout);
      fputs (_("\
\n\
If no command is given, run '${SHELL} -i' (default: '/bin/sh -i').\n\
"), stdout);
      emit_ancillary_info ();
    }
  exit (status);
}

int
main (int argc, char **argv)
{
  int c;
  char const *userspec = NULL;
  char const *groups = NULL;

  initialize_main (&argc, &argv);
  set_program_name (argv[0]);
  setlocale (LC_ALL, "");
  bindtextdomain (PACKAGE, LOCALEDIR);
  textdomain (PACKAGE);

  initialize_exit_failure (EXIT_CANCELED);
  atexit (close_stdout);

  while ((c = getopt_long (argc, argv, "+", long_opts, NULL)) != -1)
    {
      switch (c)
        {
        case USERSPEC:
          userspec = optarg;
          break;

        case GROUPS:
          groups = optarg;
          break;

        case_GETOPT_HELP_CHAR;

        case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS);

        default:
          usage (EXIT_CANCELED);
        }
    }

  if (argc <= optind)
    {
      error (0, 0, _("missing operand"));
      usage (EXIT_CANCELED);
    }

  if (chroot (argv[optind]) != 0)
    error (EXIT_CANCELED, errno, _("cannot change root directory to %s"),
           argv[optind]);

  if (chdir ("/"))
    error (EXIT_CANCELED, errno, _("cannot chdir to root directory"));

  if (argc == optind + 1)
    {
      /* No command.  Run an interactive shell.  */
      char *shell = getenv ("SHELL");
      if (shell == NULL)
        shell = bad_cast ("/bin/sh");
      argv[0] = shell;
      argv[1] = bad_cast ("-i");
      argv[2] = NULL;
    }
  else
    {
      /* The following arguments give the command.  */
      argv += optind + 1;
    }

  bool fail = false;

  /* Attempt to set all three: supplementary groups, group ID, user ID.
     Diagnose any failures.  If any have failed, exit before execvp.  */
  if (userspec)
    {
      uid_t uid = -1;
      gid_t gid = -1;
      char *user;
      char *group;
      char const *err = parse_user_spec (userspec, &uid, &gid, &user, &group);

      if (err)
        error (EXIT_CANCELED, errno, "%s", err);

      free (user);
      free (group);

      if (groups && set_additional_groups (groups))
        fail = true;

      if (gid != (gid_t) -1 && setgid (gid))
        {
          error (0, errno, _("failed to set group-ID"));
          fail = true;
        }

      if (uid != (uid_t) -1 && setuid (uid))
        {
          error (0, errno, _("failed to set user-ID"));
          fail = true;
        }
    }
  else
    {
      /* Yes, this call is identical to the one above.
         However, when --userspec and --groups groups are used together,
         we don't want to call this function until after parsing USER:GROUP,
         and it must be called before setuid.  */
      if (groups && set_additional_groups (groups))
        fail = true;
    }

  if (fail)
    exit (EXIT_CANCELED);

  /* Execute the given command.  */
  execvp (argv[0], argv);

  {
    int exit_status = (errno == ENOENT ? EXIT_ENOENT : EXIT_CANNOT_INVOKE);
    error (0, errno, _("failed to run command %s"), quote (argv[0]));
    exit (exit_status);
  }
}