Avoid using monotonic time in the DBUS_COOKIE_SHA1 authentication method

When libdbus-1 moved to using monotonic time support for the
DBUS_COOKIE_SHA1 authentication was broken, in particular
interoperability with non-libdbus-1 implementations such as GDBus.

The problem is that if monotonic clocks are available in the OS,
_dbus_get_current_time() will not return the number of seconds since
the Epoch so using it for DBUS_COOKIE_SHA1 will violate the D-Bus
specification. If both peers are using libdbus-1 it's not a problem
since both ends will use the wrong time and thus agree. However, if
the other end is another implementation and following the spec it will
not work.

First, we change _dbus_get_current_time() back so it always returns
time since the Epoch and we then rename it _dbus_get_real_time() to
make this clear. We then introduce _dbus_get_monotonic_time() and
carefully make all current users of _dbus_get_current_time() use it,
if applicable. During this audit, one of the callers,
_dbus_generate_uuid(), was currently using monotonic time but it was
decided to make it use real time instead.

Signed-off-by: David Zeuthen <davidz@redhat.com>
Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=48580

bus/connection.c

@@ -606,8 +606,8 @@ bus_connections_setup_connection (BusConnections *connections,
   d->connections = connections;
   d->connection = connection;
   
-  _dbus_get_current_time (&d->connection_tv_sec,
-                          &d->connection_tv_usec);
+  _dbus_get_monotonic_time (&d->connection_tv_sec,
+                            &d->connection_tv_usec);
   
   _dbus_assert (connection_data_slot >= 0);
   
@@ -776,7 +776,7 @@ bus_connections_expire_incomplete (BusConnections *connections)
       DBusList *link;
       int auth_timeout;
       
-      _dbus_get_current_time (&tv_sec, &tv_usec);
+      _dbus_get_monotonic_time (&tv_sec, &tv_usec);
       auth_timeout = bus_context_get_auth_timeout (connections->context);
   
       link = _dbus_list_get_first_link (&connections->incomplete);
@@ -1772,8 +1772,8 @@ bus_connections_expect_reply (BusConnections  *connections,
   cprd->pending = pending;
   cprd->connections = connections;
   
-  _dbus_get_current_time (&pending->expire_item.added_tv_sec,
-                          &pending->expire_item.added_tv_usec);
+  _dbus_get_monotonic_time (&pending->expire_item.added_tv_sec,
+                            &pending->expire_item.added_tv_usec);
 
   _dbus_verbose ("Added pending reply %p, replier %p receiver %p serial %u\n",
                  pending,

bus/expirelist.c

@@ -123,9 +123,9 @@ bus_expire_list_recheck_immediately (BusExpireList *list)
 }
 
 static int
-do_expiration_with_current_time (BusExpireList *list,
-                                 long           tv_sec,
-                                 long           tv_usec)
+do_expiration_with_monotonic_time (BusExpireList *list,
+                                   long           tv_sec,
+                                   long           tv_usec)
 {
   DBusList *link;
   int next_interval, min_wait_time, items_to_expire;
@@ -194,9 +194,9 @@ bus_expirelist_expire (BusExpireList *list)
     {
       long tv_sec, tv_usec;
 
-      _dbus_get_current_time (&tv_sec, &tv_usec);
+      _dbus_get_monotonic_time (&tv_sec, &tv_usec);
 
-      next_interval = do_expiration_with_current_time (list, tv_sec, tv_usec);
+      next_interval = do_expiration_with_monotonic_time (list, tv_sec, tv_usec);
     }
 
   bus_expire_timeout_set_interval (list->timeout, next_interval);
@@ -340,7 +340,7 @@ bus_expire_list_test (const DBusString *test_data_dir)
                               test_expire_func, NULL);
   _dbus_assert (list != NULL);
 
-  _dbus_get_current_time (&tv_sec, &tv_usec);
+  _dbus_get_monotonic_time (&tv_sec, &tv_usec);
 
   tv_sec_not_expired = tv_sec;
   tv_usec_not_expired = tv_usec;
@@ -367,22 +367,22 @@ bus_expire_list_test (const DBusString *test_data_dir)
     _dbus_assert_not_reached ("out of memory");
 
   next_interval =
-    do_expiration_with_current_time (list, tv_sec_not_expired,
-                                     tv_usec_not_expired);
+    do_expiration_with_monotonic_time (list, tv_sec_not_expired,
+                                       tv_usec_not_expired);
   _dbus_assert (item->expire_count == 0);
   _dbus_verbose ("next_interval = %d\n", next_interval);
   _dbus_assert (next_interval == 1);
   
   next_interval =
-    do_expiration_with_current_time (list, tv_sec_expired,
-                                     tv_usec_expired);
+    do_expiration_with_monotonic_time (list, tv_sec_expired,
+                                       tv_usec_expired);
   _dbus_assert (item->expire_count == 1);
   _dbus_verbose ("next_interval = %d\n", next_interval);
   _dbus_assert (next_interval == -1);
 
   next_interval =
-    do_expiration_with_current_time (list, tv_sec_past,
-                                     tv_usec_past);
+    do_expiration_with_monotonic_time (list, tv_sec_past,
+                                       tv_usec_past);
   _dbus_assert (item->expire_count == 1);
   _dbus_verbose ("next_interval = %d\n", next_interval);
   _dbus_assert (next_interval == 1000 + EXPIRE_AFTER);

dbus/dbus-connection.c

@@ -2388,7 +2388,7 @@ _dbus_connection_block_pending_call (DBusPendingCall *pending)
    * below
    */
   timeout = _dbus_pending_call_get_timeout_unlocked (pending);
-  _dbus_get_current_time (&start_tv_sec, &start_tv_usec);
+  _dbus_get_monotonic_time (&start_tv_sec, &start_tv_usec);
   if (timeout)
     {
       timeout_milliseconds = dbus_timeout_get_interval (timeout);
@@ -2445,7 +2445,7 @@ _dbus_connection_block_pending_call (DBusPendingCall *pending)
         return;
     }
   
-  _dbus_get_current_time (&tv_sec, &tv_usec);
+  _dbus_get_monotonic_time (&tv_sec, &tv_usec);
   elapsed_milliseconds = (tv_sec - start_tv_sec) * 1000 +
 	  (tv_usec - start_tv_usec) / 1000;
   

dbus/dbus-internals.c

@@ -660,7 +660,10 @@ _dbus_generate_uuid (DBusGUID *uuid)
 {
   long now;
 
-  _dbus_get_current_time (&now, NULL);
+  /* don't use monotonic time because the UUID may be saved to disk, e.g.
+   * it may persist across reboots
+   */
+  _dbus_get_real_time (&now, NULL);
 
   uuid->as_uint32s[DBUS_UUID_LENGTH_WORDS - 1] = DBUS_UINT32_TO_BE (now);
   

dbus/dbus-keyring.c

@@ -353,7 +353,7 @@ add_new_key (DBusKey  **keys_p,
       goto out;
     }
 
-  _dbus_get_current_time (&timestamp, NULL);
+  _dbus_get_real_time (&timestamp, NULL);
       
   keys[n_keys-1].id = id;
   keys[n_keys-1].creation_time = timestamp;
@@ -428,7 +428,7 @@ _dbus_keyring_reload (DBusKeyring *keyring,
   retval = FALSE;
   have_lock = FALSE;
 
-  _dbus_get_current_time (&now, NULL);
+  _dbus_get_real_time (&now, NULL);
   
   if (add_new)
     {
@@ -908,7 +908,7 @@ find_recent_key (DBusKeyring *keyring)
   int i;
   long tv_sec, tv_usec;
 
-  _dbus_get_current_time (&tv_sec, &tv_usec);
+  _dbus_get_real_time (&tv_sec, &tv_usec);
   
   i = 0;
   while (i < keyring->n_keys)

dbus/dbus-mainloop.c

@@ -91,8 +91,8 @@ timeout_callback_new (DBusTimeout         *timeout)
     return NULL;
 
   cb->timeout = timeout;
-  _dbus_get_current_time (&cb->last_tv_sec,
-                          &cb->last_tv_usec);
+  _dbus_get_monotonic_time (&cb->last_tv_sec,
+                            &cb->last_tv_usec);
   return cb;
 }
 
@@ -619,7 +619,7 @@ _dbus_loop_iterate (DBusLoop     *loop,
       unsigned long tv_sec;
       unsigned long tv_usec;
       
-      _dbus_get_current_time (&tv_sec, &tv_usec);
+      _dbus_get_monotonic_time (&tv_sec, &tv_usec);
 
       link = _dbus_list_get_first_link (&loop->timeouts);
       while (link != NULL)
@@ -728,7 +728,7 @@ _dbus_loop_iterate (DBusLoop     *loop,
       unsigned long tv_sec;
       unsigned long tv_usec;
 
-      _dbus_get_current_time (&tv_sec, &tv_usec);
+      _dbus_get_monotonic_time (&tv_sec, &tv_usec);
 
       /* It'd be nice to avoid this O(n) thingy here */
       link = _dbus_list_get_first_link (&loop->timeouts);

dbus/dbus-sysdeps-unix.c

@@ -2598,11 +2598,11 @@ _dbus_poll (DBusPollFD *fds,
  * available, to avoid problems when the system time changes.
  *
  * @param tv_sec return location for number of seconds
- * @param tv_usec return location for number of microseconds (thousandths)
+ * @param tv_usec return location for number of microseconds
  */
 void
-_dbus_get_current_time (long *tv_sec,
-                        long *tv_usec)
+_dbus_get_monotonic_time (long *tv_sec,
+                          long *tv_usec)
 {
 #ifdef HAVE_MONOTONIC_CLOCK
   struct timespec ts;
@@ -2624,6 +2624,27 @@ _dbus_get_current_time (long *tv_sec,
 #endif
 }
 
+/**
+ * Get current time, as in gettimeofday(). Never uses the monotonic
+ * clock.
+ *
+ * @param tv_sec return location for number of seconds
+ * @param tv_usec return location for number of microseconds
+ */
+void
+_dbus_get_real_time (long *tv_sec,
+                     long *tv_usec)
+{
+  struct timeval t;
+
+  gettimeofday (&t, NULL);
+
+  if (tv_sec)
+    *tv_sec = t.tv_sec;
+  if (tv_usec)
+    *tv_usec = t.tv_usec;
+}
+
 /**
  * Creates a directory; succeeds if the directory
  * is created or already existed.

dbus/dbus-sysdeps-win.c

@@ -1872,14 +1872,15 @@ _dbus_sleep_milliseconds (int milliseconds)
 
 
 /**
- * Get current time, as in gettimeofday().
+ * Get current time, as in gettimeofday(). Never uses the monotonic
+ * clock.
  *
  * @param tv_sec return location for number of seconds
  * @param tv_usec return location for number of microseconds
  */
 void
-_dbus_get_current_time (long *tv_sec,
-                        long *tv_usec)
+_dbus_get_real_time (long *tv_sec,
+                     long *tv_usec)
 {
   FILETIME ft;
   dbus_uint64_t time64;
@@ -1901,6 +1902,20 @@ _dbus_get_current_time (long *tv_sec,
     *tv_usec = time64 % 1000000;
 }
 
+/**
+ * Get current time, as in gettimeofday(). Use the monotonic clock if
+ * available, to avoid problems when the system time changes.
+ *
+ * @param tv_sec return location for number of seconds
+ * @param tv_usec return location for number of microseconds
+ */
+void
+_dbus_get_monotonic_time (long *tv_sec,
+                          long *tv_usec)
+{
+  /* no implementation yet, fall back to wall-clock time */
+  _dbus_get_real_time (tv_sec, tv_usec);
+}
 
 /**
  * signal (SIGPIPE, SIG_IGN);

dbus/dbus-sysdeps.c

@@ -508,7 +508,7 @@ _dbus_generate_pseudorandom_bytes_buffer (char *buffer,
   _dbus_verbose ("Falling back to pseudorandom for %d bytes\n",
                  n_bytes);
   
-  _dbus_get_current_time (NULL, &tv_usec);
+  _dbus_get_real_time (NULL, &tv_usec);
   srand (tv_usec);
   
   i = 0;

dbus/dbus-sysdeps.h

@@ -308,8 +308,11 @@ int _dbus_poll (DBusPollFD *fds,
 
 void _dbus_sleep_milliseconds (int milliseconds);
 
-void _dbus_get_current_time (long *tv_sec,
-                             long *tv_usec);
+void _dbus_get_real_time (long *tv_sec,
+                          long *tv_usec);
+
+void _dbus_get_monotonic_time (long *tv_sec,
+                               long *tv_usec);
 
 /**
  * directory interface

test/break-loader.c

@@ -667,7 +667,7 @@ get_random_seed (void)
 
     fprintf (stderr, "could not open/read /dev/urandom, using current time for seed\n");
 
-    _dbus_get_current_time (NULL, &tv_usec);
+    _dbus_get_monotonic_time (NULL, &tv_usec);
 
     seed = tv_usec;
   }

test/name-test/test-pending-call-dispatch.c

@@ -98,9 +98,9 @@ main (int argc, char *argv[])
     {
       long delta;
       
-      _dbus_get_current_time (&start_tv_sec, &start_tv_usec);
+      _dbus_get_monotonic_time (&start_tv_sec, &start_tv_usec);
       _run_iteration (conn);
-      _dbus_get_current_time (&end_tv_sec, &end_tv_usec);
+      _dbus_get_monotonic_time (&end_tv_sec, &end_tv_usec);
 
       /* we just care about seconds */
       delta = end_tv_sec - start_tv_sec;

test/name-test/test-pending-call-timeout.c

@@ -82,9 +82,9 @@ main (int argc, char *argv[])
     {
       long delta;
       
-      _dbus_get_current_time (&start_tv_sec, &start_tv_usec);
+      _dbus_get_monotonic_time (&start_tv_sec, &start_tv_usec);
       _run_iteration (conn);
-      _dbus_get_current_time (&end_tv_sec, &end_tv_usec);
+      _dbus_get_monotonic_time (&end_tv_sec, &end_tv_usec);
 
       /* we just care about seconds */
       delta = end_tv_sec - start_tv_sec;