Add a workaround for bug where some initial join events don't referen…

…ce creation events in their auth_events

synapse/handlers/federation.py

@@ -21,7 +21,7 @@
 from synapse.api.errors import (
     AuthError, FederationError, SynapseError, StoreError,
 )
-from synapse.api.events.room import RoomMemberEvent
+from synapse.api.events.room import RoomMemberEvent, RoomCreateEvent
 from synapse.api.constants import Membership
 from synapse.util.logutils import log_function
 from synapse.util.async import run_on_reactor
@@ -618,6 +618,12 @@ def _handle_new_event(self, event, state=None, backfilled=False,
 
                 auth_events[(e.type, e.state_key)] = e
 
+            if event.type == RoomMemberEvent.TYPE and not event.auth_events:
+                if len(event.prev_events) == 1:
+                    c = yield self.store.get_event(event.prev_events[0][0])
+                    if c.type == RoomCreateEvent.TYPE:
+                        auth_events[(c.type, c.state_key)] = c
+
         self.auth.check(event, auth_events=auth_events)
 
         yield self.store.persist_event(