2 files changed, 16 insertions, 1 deletions
diff --git a/changelog.d/15080.bugfix b/changelog.d/15080.bugfix
new file mode 100644
index 0000000000..965d0b921e
--- /dev/null
+++ b/changelog.d/15080.bugfix
@@ -0,0 +1 @@
+Reduce the likelihood of a rare race condition where rejoining a restricted room over federation would fail.
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 1d0f6bcd6f..5f2057269d 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -952,7 +952,20 @@ class FederationHandler:
#
# Note that this requires the /send_join request to come back to the
# same server.
+ prev_event_ids = None
if room_version.msc3083_join_rules:
+ # Note that the room's state can change out from under us and render our
+ # nice join rules-conformant event non-conformant by the time we build the
+ # event. When this happens, our validation at the end fails and we respond
+ # to the requesting server with a 403, which is misleading — it indicates
+ # that the user is not allowed to join the room and the joining server
+ # should not bother retrying via this homeserver or any others, when
+ # in fact we've just messed up with building the event.
+ #
+ # To reduce the likelihood of this race, we capture the forward extremities
+ # of the room (prev_event_ids) just before fetching the current state, and
+ # hope that the state we fetch corresponds to the prev events we chose.
+ prev_event_ids = await self.store.get_prev_events_for_room(room_id)
state_ids = await self._state_storage_controller.get_current_state_ids(
room_id
)
@@ -994,7 +1007,8 @@ class FederationHandler:
event,
unpersisted_context,
) = await self.event_creation_handler.create_new_client_event(
- builder=builder
+ builder=builder,
+ prev_event_ids=prev_event_ids,
)
except SynapseError as e:
logger.warning("Failed to create join to %s because %s", room_id, e)
|
