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Merge branch 'wip/pwithnall/1954-dbus-keyring-handling' into 'master'

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Fix TOCTTOU races in D-Bus SHA-1 auth mechanism

Closes #1954

See merge request GNOME/glib!1477
This commit is contained in:
Simon McVittie 2020-05-05 16:07:28 +00:00
commit 3b3026b763
2 changed files with 118 additions and 101 deletions
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205
gio/gdbusauthmechanismsha1.c
View File

@ -234,6 +234,9 @@ ensure_keyring_directory (GError **error)
{
gchar *path;
const gchar *e;
#ifdef G_OS_UNIX
struct stat statbuf;
#endif
g_return_val_if_fail (error == NULL || *error == NULL, NULL);
@ -249,48 +252,54 @@ ensure_keyring_directory (GError **error)
NULL);
}
#ifdef G_OS_UNIX
if (stat (path, &statbuf) != 0)
{
int errsv = errno;
if (errsv != ENOENT)
{
g_set_error (error,
G_IO_ERROR,
g_io_error_from_errno (errsv),
_("Error when getting information for directory “%s”: %s"),
path,
g_strerror (errsv));
g_clear_pointer (&path, g_free);
return NULL;
}
}
else if (S_ISDIR (statbuf.st_mode))
{
if (g_getenv ("G_DBUS_COOKIE_SHA1_KEYRING_DIR_IGNORE_PERMISSION") == NULL &&
(statbuf.st_mode & 0777) != 0700)
{
g_set_error (error,
G_IO_ERROR,
G_IO_ERROR_FAILED,
_("Permissions on directory “%s” are malformed. Expected mode 0700, got 0%o"),
path,
(guint) (statbuf.st_mode & 0777));
g_clear_pointer (&path, g_free);
return NULL;
}
return g_steal_pointer (&path);
}
#else /* if !G_OS_UNIX */
/* On non-Unix platforms, check that it exists as a directory, but don’t do
* permissions checks at the moment. */
if (g_file_test (path, G_FILE_TEST_EXISTS | G_FILE_TEST_IS_DIR))
{
if (g_getenv ("G_DBUS_COOKIE_SHA1_KEYRING_DIR_IGNORE_PERMISSION") == NULL)
{
#ifdef G_OS_UNIX
struct stat statbuf;
if (stat (path, &statbuf) != 0)
{
int errsv = errno;
g_set_error (error,
G_IO_ERROR,
g_io_error_from_errno (errsv),
_("Error when getting information for directory “%s”: %s"),
path,
g_strerror (errsv));
g_free (path);
path = NULL;
goto out;
}
if ((statbuf.st_mode & 0777) != 0700)
{
g_set_error (error,
G_IO_ERROR,
G_IO_ERROR_FAILED,
_("Permissions on directory “%s” are malformed. Expected mode 0700, got 0%o"),
path,
(guint) (statbuf.st_mode & 0777));
g_free (path);
path = NULL;
goto out;
}
#else
#ifdef __GNUC__
#pragma GCC diagnostic push
#pragma GCC diagnostic warning "-Wcpp"
#warning Please implement permission checking on this non-UNIX platform
#pragma GCC diagnostic pop
#endif
#endif
}
goto out;
#endif /* __GNUC__ */
return g_steal_pointer (&path);
}
#endif /* if !G_OS_UNIX */
if (g_mkdir_with_parents (path, 0700) != 0)
{
@ -301,13 +310,11 @@ ensure_keyring_directory (GError **error)
_("Error creating directory “%s”: %s"),
path,
g_strerror (errsv));
g_free (path);
path = NULL;
goto out;
g_clear_pointer (&path, g_free);
return NULL;
}
out:
return path;
return g_steal_pointer (&path);
}
/* ---------------------------------------------------------------------------------------------------- */
@ -450,25 +457,52 @@ _log (const gchar *message,
g_free (s);
}
/* Returns FD for lock file, if it was created exclusively (didn't exist already,
* and was created successfully) */
static gint
create_lock_exclusive (const gchar *lock_path,
GError **error)
{
int errsv;
gint ret;
ret = g_open (lock_path, O_CREAT | O_EXCL, 0600);
errsv = errno;
if (ret < 0)
{
g_set_error (error,
G_IO_ERROR,
g_io_error_from_errno (errsv),
_("Error creating lock file “%s”: %s"),
lock_path,
g_strerror (errsv));
return -1;
}
return ret;
}
static gint
keyring_acquire_lock (const gchar *path,
GError **error)
{
gchar *lock;
gchar *lock = NULL;
gint ret;
guint num_tries;
#ifdef EEXISTS
guint num_create_tries;
#endif
int errsv;
g_return_val_if_fail (path != NULL, FALSE);
g_return_val_if_fail (error == NULL || *error == NULL, FALSE);
/* Total possible sleep period = max_tries * timeout_usec = 0.5s */
const guint max_tries = 50;
const guint timeout_usec = 1000 * 10;
g_return_val_if_fail (path != NULL, -1);
g_return_val_if_fail (error == NULL || *error == NULL, -1);
ret = -1;
lock = g_strdup_printf ("%s.lock", path);
lock = g_strconcat (path, ".lock", NULL);
/* This is what the D-Bus spec says
* (https://dbus.freedesktop.org/doc/dbus-specification.html#auth-mechanisms-sha)
*
* Create a lockfile name by appending ".lock" to the name of the
* cookie file. The server should attempt to create this file using
@ -481,66 +515,43 @@ keyring_acquire_lock (const gchar *path,
* real locking implementations are still flaky on network filesystems
*/
#ifdef EEXISTS
num_create_tries = 0;
again:
#endif
num_tries = 0;
while (g_file_test (lock, G_FILE_TEST_EXISTS))
for (num_tries = 0; num_tries < max_tries; num_tries++)
{
/* Ignore the error until the final call. */
ret = create_lock_exclusive (lock, NULL);
if (ret >= 0)
break;
/* sleep 10ms, then try again */
g_usleep (1000*10);
num_tries++;
if (num_tries == 50)
{
/* ok, we slept 50*10ms = 0.5 seconds. Conclude that the lock file must be
* stale (nuke the it from orbit)
*/
if (g_unlink (lock) != 0)
{
errsv = errno;
g_set_error (error,
G_IO_ERROR,
g_io_error_from_errno (errsv),
_("Error deleting stale lock file “%s”: %s"),
lock,
g_strerror (errsv));
goto out;
}
_log ("Deleted stale lock file '%s'", lock);
break;
}
g_usleep (timeout_usec);
}
ret = g_open (lock, O_CREAT |
#ifdef O_EXCL
O_EXCL,
#else
0,
#endif
0700);
errsv = errno;
if (ret == -1)
if (num_tries == max_tries)
{
#ifdef EEXISTS
/* EEXIST: pathname already exists and O_CREAT and O_EXCL were used. */
if (errsv == EEXISTS)
/* ok, we slept 50*10ms = 0.5 seconds. Conclude that the lock file must be
* stale (nuke it from orbit)
*/
if (g_unlink (lock) != 0)
{
num_create_tries++;
if (num_create_tries < 5)
goto again;
errsv = errno;
g_set_error (error,
G_IO_ERROR,
g_io_error_from_errno (errsv),
_("Error deleting stale lock file “%s”: %s"),
lock,
g_strerror (errsv));
goto out;
}
#endif
g_set_error (error,
G_IO_ERROR,
g_io_error_from_errno (errsv),
_("Error creating lock file “%s”: %s"),
lock,
g_strerror (errsv));
goto out;
_log ("Deleted stale lock file '%s'", lock);
/* Try one last time to create it, now that we've deleted the stale one */
ret = create_lock_exclusive (lock, error);
if (ret < 0)
goto out;
}
out:
out:
g_free (lock);
return ret;
}

14
gio/tests/gdbus-server-auth.c
View File

@ -152,6 +152,7 @@ whoami_filter_cb (GDBusConnection *connection,
g_dbus_connection_send_message (connection, reply,
G_DBUS_SEND_MESSAGE_FLAGS_NONE,
NULL, NULL);
g_object_unref (reply);
/* handled */
g_object_unref (message);
@ -397,6 +398,14 @@ do_test_server_auth (InteropFlags flags)
LibdbusCall libdbus_call = { DBUS_ERROR_INIT, NULL, NULL, NULL };
GTask *task;
/* The test suite uses %G_TEST_OPTION_ISOLATE_DIRS, which sets
* `HOME=/dev/null` and leaves g_get_home_dir() pointing to the per-test
* temp home directory. Unfortunately, libdbus doesn’t allow the home dir
* to be overridden except using the environment, so copy the per-test
* temp home directory back there so that libdbus uses the same
* `$HOME/.dbus-keyrings` path as GLib. This is not thread-safe. */
g_setenv ("HOME", g_get_home_dir (), TRUE);
libdbus_call.conn = dbus_connection_open_private (connectable_address,
&libdbus_call.error);
g_assert_cmpstr (libdbus_call.error.name, ==, NULL);
@ -515,10 +524,7 @@ int
main (int argc,
char *argv[])
{
/* FIXME: Add debug for https://gitlab.gnome.org/GNOME/glib/issues/1954 */
g_setenv ("G_DBUS_DEBUG", "all", TRUE);
g_test_init (&argc, &argv, NULL);
g_test_init (&argc, &argv, G_TEST_OPTION_ISOLATE_DIRS, NULL);
g_test_add_func ("/gdbus/server-auth", test_server_auth);
g_test_add_func ("/gdbus/server-auth/abstract", test_server_auth_abstract);