Fix hierarchy returning 403 when room is accessible through federation

changelog.d/17194.bugfix

@@ -0,0 +1 @@
+Fix hierarchy returning 403 when room is accessible through federation. Contributed by Krishan (@kfiven).

synapse/handlers/room_summary.py

@@ -183,15 +183,37 @@ async def _get_room_hierarchy(
     ) -> 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):
+        # First of all, check that the room is accessible locally.
+        # OR accessible through federation.
+        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"
                 % (requester, requested_room_id),
                 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:

tests/handlers/test_room_summary.py

@@ -757,6 +757,54 @@ async def summarize_remote_room_hierarchy(
             )
         self._assert_hierarchy(result, expected)
 
+    def test_fed_root(self) -> None:
+        """
+        Test if requested room is available over federation.
+        """
+        fed_hostname = self.hs.hostname + "2"
+        fed_space = "#fed_space:" + fed_hostname
+        fed_subroom = "#fed_sub_room:" + fed_hostname
+
+        requested_room_entry = _RoomEntry(
+            fed_space,
+            {
+                "room_id": fed_space,
+                "world_readable": True,
+                "room_type": RoomTypes.SPACE,
+            },
+            [
+                {
+                    "type": EventTypes.SpaceChild,
+                    "room_id": fed_space,
+                    "state_key": fed_subroom,
+                    "content": {"via": [fed_hostname]},
+                }
+            ],
+        )
+        child_room = {
+            "room_id": fed_subroom,
+            "world_readable": True,
+        }
+
+        async def summarize_remote_room_hierarchy(
+            _self: Any, room: Any, suggested_only: bool
+        ) -> Tuple[Optional[_RoomEntry], Dict[str, JsonDict], Set[str]]:
+            return requested_room_entry, {fed_subroom: child_room}, set()
+
+        expected = [
+            (fed_space, [fed_subroom]),
+            (fed_subroom, ()),
+        ]
+
+        with mock.patch(
+            "synapse.handlers.room_summary.RoomSummaryHandler._summarize_remote_room_hierarchy",
+            new=summarize_remote_room_hierarchy,
+        ):
+            result = self.get_success(
+                self.handler.get_room_hierarchy(create_requester(self.user), fed_space)
+            )
+        self._assert_hierarchy(result, expected)
+
     def test_fed_filtering(self) -> None:
         """
         Rooms returned over federation should be properly filtered to only include