Fix hierarchy returning 403 when room is accessible through federation (#17194)

1 files changed, 23 insertions, 2 deletions

diff --git a/synapse/handlers/room_summary.py b/synapse/handlers/room_summary.py

index 720459f1e7..64f5bea014 100644
--- a/synapse/handlers/room_summary.py
+++ b/synapse/handlers/room_summary.py
@@ -183,8 +183,13 @@ class RoomSummaryHandler:
     ) -> JsonDict:
         """See docstring for SpaceSummaryHandler.get_room_hierarchy."""
 
-        # First of all, check that the room is accessible.
-        if not await self._is_local_room_accessible(requested_room_id, requester):
+        # If the room is available locally, quickly check that the user can access it.
+        local_room = await self._store.is_host_joined(
+            requested_room_id, self._server_name
+        )
+        if local_room and not await self._is_local_room_accessible(
+            requested_room_id, requester
+        ):
             raise UnstableSpecAuthError(
                 403,
                 "User %s not in room %s, and room previews are disabled"
@@ -192,6 +197,22 @@ class RoomSummaryHandler:
                 errcode=Codes.NOT_JOINED,
             )
 
+        if not local_room:
+            room_hierarchy = await self._summarize_remote_room_hierarchy(
+                _RoomQueueEntry(requested_room_id, ()),
+                False,
+            )
+            root_room_entry = room_hierarchy[0]
+            if not root_room_entry or not await self._is_remote_room_accessible(
+                requester, requested_room_id, root_room_entry.room
+            ):
+                raise UnstableSpecAuthError(
+                    403,
+                    "User %s not in room %s, and room previews are disabled"
+                    % (requester, requested_room_id),
+                    errcode=Codes.NOT_JOINED,
+                )
+
         # If this is continuing a previous session, pull the persisted data.
         if from_token:
             try: