flatpak-builder/app/xdg-app-builtins-enter.c

/*
 * Copyright © 2014 Red Hat, Inc
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library. If not, see <http://www.gnu.org/licenses/>.
 *
 * Authors:
 *       Alexander Larsson <alexl@redhat.com>
 */

#include "config.h"

#include <locale.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>

#include "libgsystem.h"
#include "libglnx/libglnx.h"

#include "xdg-app-builtins.h"
#include "xdg-app-utils.h"
#include "xdg-app-dbus.h"
#include "xdg-app-run.h"


static GOptionEntry options[] = {
  { NULL }
};

static gboolean
write_to_file (int fd, const char *content, ssize_t len)
{
  ssize_t res;

  while (len > 0)
    {
      res = write (fd, content, len);
      if (res < 0 && errno == EINTR)
        continue;
      if (res <= 0)
        return FALSE;
      len -= res;
      content += res;
    }

  return TRUE;
}

static gboolean
write_file (const char *path, const char *content)
{
  int fd;
  gboolean res;
  int errsv;

  fd = open (path, O_RDWR | O_CLOEXEC, 0);
  if (fd == -1)
    return FALSE;

  res = TRUE;
  if (content)
    res = write_to_file (fd, content, strlen (content));

  errsv = errno;
  close (fd);
  errno = errsv;

  return res;
}

static uid_t uid;
static gid_t gid;

static void
child_setup (gpointer user_data)
{
  g_autofree char *uid_map = NULL;
  g_autofree char *gid_map = NULL;
  uid_t ns_uid;
  gid_t ns_gid;

  ns_uid = getuid ();
  ns_gid = getgid ();

  if (ns_uid != uid || ns_gid != gid)
    {
      /* Work around user namespace devpts issue by creating a new
         userspace and map our uid like the helper does */

      if (unshare (CLONE_NEWUSER))
        {
          g_warning ("Can't unshare user namespace: %s", strerror (errno));
          return;
        }

      uid_map = g_strdup_printf ("%d %d 1\n", uid, ns_uid);
      if (!write_file ("/proc/self/uid_map", uid_map))
        g_warning ("setting up uid map");

      gid_map = g_strdup_printf ("%d %d 1\n", gid, ns_gid);
      if (!write_file ("/proc/self/gid_map", gid_map))
        g_warning ("setting up gid map");
    }
}

gboolean
flatpak_builtin_enter (int           argc,
                       char        **argv,
                       GCancellable *cancellable,
                       GError      **error)
{
  g_autoptr(GOptionContext) context = NULL;
  int rest_argv_start, rest_argc;
  g_autoptr(FlatpakContext) arg_context = NULL;
  const char *ns_name[5] = { "user", "ipc", "net", "pid", "mnt" };
  int ns_fd[G_N_ELEMENTS (ns_name)];
  char pid_ns[256];
  ssize_t pid_ns_len;
  char self_ns[256];
  ssize_t self_ns_len;
  char *pid_s;
  int pid, i;
  g_autofree char *environment_path = NULL;
  g_autoptr(GPtrArray) argv_array = NULL;
  g_autoptr(GPtrArray) envp_array = NULL;
  g_autofree char *environment = NULL;
  gsize environment_len;
  char *e;
  g_autofree char *pulse_path = NULL;
  g_autofree char *session_bus_path = NULL;
  g_autofree char *xdg_runtime_dir = NULL;
  int status;

  uid = getuid ();
  gid = getgid ();

  context = g_option_context_new ("MONITORPID [COMMAND [args...]] - Run a command inside a running sandbox");

  rest_argc = 0;
  for (i = 1; i < argc; i++)
    {
      /* The non-option is the command, take it out of the arguments */
      if (argv[i][0] != '-')
        {
          rest_argv_start = i;
          rest_argc = argc - i;
          argc = i;
          break;
        }
    }

  arg_context = flatpak_context_new ();
  g_option_context_add_group (context, flatpak_context_get_options (arg_context));

  if (!flatpak_option_context_parse (context, options, &argc, &argv, FLATPAK_BUILTIN_FLAG_NO_DIR, NULL, cancellable, error))
    return FALSE;

  if (rest_argc < 2)
    {
      usage_error (context, "MONITORPID and COMMAND must be specified", error);
      return FALSE;
    }

  pid_s = argv[rest_argv_start];

  pid = atoi (pid_s);
  if (pid <= 0)
    return flatpak_fail (error, "Invalid pid %s\n", pid_s);

  environment_path = g_strdup_printf ("/proc/%d/environ", pid);
  if (!g_file_get_contents (environment_path, &environment, &environment_len, error))
    return FALSE;

  for (i = 0; i < G_N_ELEMENTS (ns_name); i++)
    {
      g_autofree char *path = g_strdup_printf ("/proc/%d/ns/%s", pid, ns_name[i]);
      g_autofree char *self_path = g_strdup_printf ("/proc/self/ns/%s", ns_name[i]);

      pid_ns_len = readlink (path, pid_ns, sizeof (pid_ns) - 1);
      if (pid_ns_len <= 0)
        return flatpak_fail (error, "Invalid %s namespace for pid %d\n", ns_name[i], pid);
      pid_ns[pid_ns_len] = 0;

      self_ns_len = readlink (self_path, self_ns, sizeof (self_ns) - 1);
      if (self_ns_len <= 0)
        return flatpak_fail (error, "Invalid %s namespace for self\n", ns_name[i]);
      self_ns[self_ns_len] = 0;

      if (strcmp (self_ns, pid_ns) == 0)
        {
          /* No need to setns to the same namespace, it will only fail */
          ns_fd[i] = -1;
        }
      else
        {
          ns_fd[i] = open (path, O_RDONLY);
          if (ns_fd[i] == -1)
            return flatpak_fail (error, "Can't open %s namespace: %s", ns_name[i], strerror (errno));
        }
    }

  for (i = 0; i < G_N_ELEMENTS (ns_fd); i++)
    {
      if (ns_fd[i] != -1)
        {
          if (setns (ns_fd[i], 0) == -1)
            return flatpak_fail (error, "Can't enter %s namespace: %s", ns_name[i], strerror (errno));
          close (ns_fd[i]);
        }
    }

  envp_array = g_ptr_array_new_with_free_func (g_free);
  for (e = environment; e < environment + environment_len; e = e + strlen (e) + 1)
    {
      if (*e != 0 &&
          !g_str_has_prefix (e, "DISPLAY=") &&
          !g_str_has_prefix (e, "PULSE_SERVER=") &&
          !g_str_has_prefix (e, "PULSE_CLIENTCONFIG=") &&
          !g_str_has_prefix (e, "XDG_RUNTIME_DIR=") &&
          !g_str_has_prefix (e, "DBUS_SYSTEM_BUS_ADDRESS=") &&
          !g_str_has_prefix (e, "DBUS_SESSION_BUS_ADDRESS="))
        {
          if (g_str_has_prefix (e, "_LD_LIBRARY_PATH="))
            e++;
          g_ptr_array_add (envp_array, g_strdup (e));
        }
    }

  xdg_runtime_dir = g_strdup_printf ("/run/user/%d", uid);
  g_ptr_array_add (envp_array, g_strdup_printf ("XDG_RUNTIME_DIR=%s", xdg_runtime_dir));

  if (g_file_test ("/tmp/.X11-unix/X99", G_FILE_TEST_EXISTS))
    g_ptr_array_add (envp_array, g_strdup ("DISPLAY=:99.0"));

  pulse_path = g_strdup_printf ("/run/user/%d/pulse/native", uid);
  if (g_file_test (pulse_path, G_FILE_TEST_EXISTS))
    {
      g_ptr_array_add (envp_array, g_strdup_printf ("PULSE_SERVER=unix:%s", pulse_path));
      g_ptr_array_add (envp_array, g_strdup_printf ("PULSE_CLIENTCONFIG=/run/user/%d/pulse/config", uid));
    }

  session_bus_path = g_strdup_printf ("/run/user/%d/bus", uid);
  if (g_file_test (session_bus_path, G_FILE_TEST_EXISTS))
    g_ptr_array_add (envp_array, g_strdup_printf ("DBUS_SESSION_BUS_ADDRESS=unix:%s", session_bus_path));

  if (g_file_test ("/run/dbus/system_bus_socket", G_FILE_TEST_EXISTS))
    g_ptr_array_add (envp_array, g_strdup ("DBUS_SYSTEM_BUS_ADDRESS=unix:/run/dbus/system_bus_socket"));

  g_ptr_array_add (envp_array, NULL);

  argv_array = g_ptr_array_new_with_free_func (g_free);
  for (i = 1; i < rest_argc; i++)
    g_ptr_array_add (argv_array, g_strdup (argv[rest_argv_start + i]));
  g_ptr_array_add (argv_array, NULL);

  if (!g_spawn_sync (NULL, (char **) argv_array->pdata, (char **) envp_array->pdata,
                     G_SPAWN_SEARCH_PATH_FROM_ENVP | G_SPAWN_CHILD_INHERITS_STDIN,
                     child_setup, NULL,
                     NULL, NULL,
                     &status, error))
    return FALSE;

  exit (status);
}