Add check_room_id to more store functions which get events

Use it when retrieving missing events in state DAG mode.

synapse/handlers/federation.py

@@ -1983,7 +1983,7 @@ class FederationHandler:
         limit = min(limit, StateDag.MAX_MISSING_EVENTS)
         earliest_event_set = set(earliest_events)
 
-        seed_events = await self.store.get_events(latest_events)
+        seed_events = await self.store.get_events(latest_events, check_room_id=room_id)
 
         seed_event_ids: list[str] = []
         first_hop_event_ids: set[str] = set()
@@ -2007,7 +2007,8 @@ class FederationHandler:
         first_hop_events: list[EventBase] = []
         if first_hop_event_ids:
             first_hop_events = await self.store.get_events_as_list(
-                sorted(first_hop_event_ids)
+                sorted(first_hop_event_ids),
+                check_room_id=room_id,
             )
             # the sort exists to make [:limit] truncation deterministic
             first_hop_events.sort(key=lambda ev: ev.event_id)

synapse/storage/databases/main/events_worker.py

@@ -611,6 +611,7 @@ class EventsWorkerStore(SQLBaseStore):
         redact_behaviour: EventRedactBehaviour = EventRedactBehaviour.redact,
         get_prev_content: bool = False,
         allow_rejected: bool = False,
+        check_room_id: str | None = None,
     ) -> dict[str, EventBase]:
         """Get events from the database
 
@@ -633,6 +634,9 @@ class EventsWorkerStore(SQLBaseStore):
             allow_rejected: If True, return rejected events. Otherwise,
                 omits rejected events from the response.
 
+            check_room_id: if not None, check the room ID of the events in `event_ids`.
+                If there is a mismatch, drop that event.
+
         Returns:
             A mapping from event_id to event.
         """
@@ -646,6 +650,7 @@ class EventsWorkerStore(SQLBaseStore):
             redact_behaviour=redact_behaviour,
             get_prev_content=get_prev_content,
             allow_rejected=allow_rejected,
+            check_room_id=check_room_id,
         )
 
         return {e.event_id: e for e in events}
@@ -659,6 +664,7 @@ class EventsWorkerStore(SQLBaseStore):
         redact_behaviour: EventRedactBehaviour = EventRedactBehaviour.redact,
         get_prev_content: bool = False,
         allow_rejected: bool = False,
+        check_room_id: str | None = None,
     ) -> list[EventBase]:
         """Get events from the database and return in a list in the same order
         as given by `event_ids` arg.
@@ -681,6 +687,9 @@ class EventsWorkerStore(SQLBaseStore):
             allow_rejected: If True, return rejected events. Otherwise,
                 omits rejected events from the response.
 
+            check_room_id: if not None, check the room ID of the events in `event_ids`.
+                If there is a mismatch, drop that event.
+
         Returns:
             List of events fetched from the database. The events are in the same
             order as `event_ids` arg.
@@ -707,6 +716,9 @@ class EventsWorkerStore(SQLBaseStore):
             if not entry:
                 continue
 
+            if check_room_id is not None and entry.event.room_id != check_room_id:
+                continue
+
             if not allow_rejected:
                 assert not entry.event.rejected_reason, (
                     "rejected event returned from _get_events_from_cache_or_db despite "

tests/federation/test_federation_server.py

@@ -584,6 +584,52 @@ class GetMissingEventsStateDagTests(unittest.FederatingHomeserverTestCase):
         )
         self.assertEqual(events, [])
 
+    def test_ignores_non_state_seed_from_other_state_dag_room(self) -> None:
+        """
+        A non-state seed from another state DAG room, which the remote server is not
+        joined to, must not have its `prev_state_events` returned.
+        """
+        other_room_id = self.helper.create_room_as(
+            room_creator=self.local_user_id,
+            tok=self.local_user_token,
+            room_version=RoomVersions.MSC4242v12.identifier,
+        )
+        other_message_id = self.helper.send(
+            other_room_id, body="secret", tok=self.local_user_token
+        )["event_id"]
+
+        # This uses self.room_id as the room ID
+        events = self._get_missing_events(
+            earliest_events=[],
+            latest_events=[other_message_id],
+            walk_state_dag=True,
+            limit=20,
+        )
+        self.assertEqual(events, [])
+
+    def test_ignores_non_state_seed_from_non_state_dag_room(self) -> None:
+        """
+        A non-state seed from a room which has no state DAG is treated as unknown,
+        rather than failing the request.
+        """
+        other_room_id = self.helper.create_room_as(
+            room_creator=self.local_user_id,
+            tok=self.local_user_token,
+            room_version=RoomVersions.V12.identifier,
+        )
+        other_message_id = self.helper.send(
+            other_room_id, body="hello", tok=self.local_user_token
+        )["event_id"]
+
+        # This uses self.room_id as the room ID
+        events = self._get_missing_events(
+            earliest_events=[],
+            latest_events=[other_message_id],
+            walk_state_dag=True,
+            limit=20,
+        )
+        self.assertEqual(events, [])
+
 
 class MessageAcceptTests(unittest.FederatingHomeserverTestCase):
     """