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

13 files changed, 83 insertions, 41 deletions

diff --git a/bus/connection.c b/bus/connection.c
index 97e5f64b..d69758c9 100644
--- a/bus/connection.c
+++ b/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,
diff --git a/bus/expirelist.c b/bus/expirelist.c
index 3c87c119..1a12ea45 100644
--- a/bus/expirelist.c
+++ b/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);
diff --git a/dbus/dbus-connection.c b/dbus/dbus-connection.c
index ac0b2c0e..ee33b6cc 100644
--- a/dbus/dbus-connection.c
+++ b/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;
   
diff --git a/dbus/dbus-internals.c b/dbus/dbus-internals.c
index a5db1460..0e5d807e 100644
--- a/dbus/dbus-internals.c
+++ b/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);
   
diff --git a/dbus/dbus-keyring.c b/dbus/dbus-keyring.c
index 35e8d74e..23b9df5a 100644
--- a/dbus/dbus-keyring.c
+++ b/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)
diff --git a/dbus/dbus-mainloop.c b/dbus/dbus-mainloop.c
index 8a30f7fe..cef676a3 100644
--- a/dbus/dbus-mainloop.c
+++ b/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);
diff --git a/dbus/dbus-sysdeps-unix.c b/dbus/dbus-sysdeps-unix.c
index 9fddca73..cef8bd31 100644
--- a/dbus/dbus-sysdeps-unix.c
+++ b/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;
@@ -2625,6 +2625,27 @@ _dbus_get_current_time (long *tv_sec,
 }
 
 /**
+ * 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.
  *
diff --git a/dbus/dbus-sysdeps-win.c b/dbus/dbus-sysdeps-win.c
index e30e92fe..397520af 100644
--- a/dbus/dbus-sysdeps-win.c
+++ b/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);
diff --git a/dbus/dbus-sysdeps.c b/dbus/dbus-sysdeps.c
index 1a93cea7..861bfec9 100644
--- a/dbus/dbus-sysdeps.c
+++ b/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;
diff --git a/dbus/dbus-sysdeps.h b/dbus/dbus-sysdeps.h
index f8438f43..c03e2f54 100644
--- a/dbus/dbus-sysdeps.h
+++ b/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
diff --git a/test/break-loader.c b/test/break-loader.c
index 542f36ff..e62b8c20 100644
--- a/test/break-loader.c
+++ b/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;
   }
diff --git a/test/name-test/test-pending-call-dispatch.c b/test/name-test/test-pending-call-dispatch.c
index 57582d49..c8b5a467 100644
--- a/test/name-test/test-pending-call-dispatch.c
+++ b/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;
diff --git a/test/name-test/test-pending-call-timeout.c b/test/name-test/test-pending-call-timeout.c
index 381113bd..d051faba 100644
--- a/test/name-test/test-pending-call-timeout.c
+++ b/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;