Do not allow cross-room relations, per MSC2674.

synapse/events/utils.py

@@ -454,6 +454,7 @@ async def _injected_bundled_aggregations(
                 return
 
         event_id = event.event_id
+        room_id = event.room_id
 
         # The bundled aggregations to include.
         aggregations = {}
@@ -463,7 +464,7 @@ async def _injected_bundled_aggregations(
             aggregations[RelationTypes.ANNOTATION] = annotations.to_dict()
 
         references = await self.store.get_relations_for_event(
-            event_id, RelationTypes.REFERENCE, direction="f"
+            event_id, room_id, RelationTypes.REFERENCE, direction="f"
         )
         if references.chunk:
             aggregations[RelationTypes.REFERENCE] = references.to_dict()

synapse/rest/client/relations.py

@@ -212,6 +212,7 @@ async def on_GET(
 
             pagination_chunk = await self.store.get_relations_for_event(
                 event_id=parent_id,
+                room_id=room_id,
                 relation_type=relation_type,
                 event_type=event_type,
                 limit=limit,
@@ -383,7 +384,9 @@ async def on_GET(
 
         # This checks that a) the event exists and b) the user is allowed to
         # view it.
-        await self.event_handler.get_event(requester.user, room_id, parent_id)
+        event = await self.event_handler.get_event(requester.user, room_id, parent_id)
+        if event is None:
+            raise SynapseError(404, "Unknown parent event.")
 
         if relation_type != RelationTypes.ANNOTATION:
             raise SynapseError(400, "Relation type must be 'annotation'")
@@ -402,6 +405,7 @@ async def on_GET(
 
         result = await self.store.get_relations_for_event(
             event_id=parent_id,
+            room_id=room_id,
             relation_type=relation_type,
             event_type=event_type,
             aggregation_key=key,

synapse/storage/databases/main/relations.py

@@ -37,6 +37,7 @@ class RelationsWorkerStore(SQLBaseStore):
     async def get_relations_for_event(
         self,
         event_id: str,
+        room_id: str,
         relation_type: Optional[str] = None,
         event_type: Optional[str] = None,
         aggregation_key: Optional[str] = None,
@@ -49,6 +50,7 @@ async def get_relations_for_event(
 
         Args:
             event_id: Fetch events that relate to this event ID.
+            room_id: The room the event belongs to.
             relation_type: Only fetch events with this relation type, if given.
             event_type: Only fetch events with this event type, if given.
             aggregation_key: Only fetch events with this aggregation key, if given.
@@ -63,8 +65,8 @@ async def get_relations_for_event(
             the form `{"event_id": "..."}`.
         """
 
-        where_clause = ["relates_to_id = ?"]
-        where_args: List[Union[str, int]] = [event_id]
+        where_clause = ["relates_to_id = ?", "room_id = ?"]
+        where_args: List[Union[str, int]] = [event_id, room_id]
 
         if relation_type is not None:
             where_clause.append("relation_type = ?")

tests/rest/client/test_relations.py

@@ -16,13 +16,15 @@
 import itertools
 import urllib.parse
 from typing import Dict, List, Optional, Tuple
+from unittest.mock import patch
 
 from synapse.api.constants import EventTypes, RelationTypes
 from synapse.rest import admin
 from synapse.rest.client import login, register, relations, room, sync
 
 from tests import unittest
 from tests.server import FakeChannel
+from tests.test_utils.event_injection import inject_event
 
 
 class RelationsTestCase(unittest.HomeserverTestCase):
@@ -651,6 +653,60 @@ def test_aggregation_get_event_for_thread(self):
             },
         )
 
+    def test_ignore_invalid_room(self):
+        """Test that we ignore invalid relations over federation."""
+        # Create another room and send a message in it.
+        room2 = self.helper.create_room_as(self.user_id, tok=self.user_token)
+        res = self.helper.send(room2, body="Hi!", tok=self.user_token)
+        parent_id = res["event_id"]
+
+        # Disable the validation to pretend this came over federation.
+        with patch(
+            "synapse.handlers.message.EventCreationHandler._validate_event_relation"
+        ):
+            self.get_success(
+                inject_event(
+                    self.hs,
+                    room_id=self.room,
+                    type="m.reaction",
+                    sender=self.user_id,
+                    content={
+                        "m.relates_to": {
+                            "rel_type": RelationTypes.ANNOTATION,
+                            "event_id": parent_id,
+                            "key": "A",
+                        }
+                    },
+                )
+            )
+
+        # They should be ignored when fetching relations.
+        channel = self.make_request(
+            "GET",
+            f"/_matrix/client/unstable/rooms/{room2}/relations/{parent_id}",
+            access_token=self.user_token,
+        )
+        self.assertEquals(200, channel.code, channel.json_body)
+        self.assertEqual(channel.json_body["chunk"], [])
+
+        # And when fetching aggregations.
+        channel = self.make_request(
+            "GET",
+            f"/_matrix/client/unstable/rooms/{room2}/aggregations/{parent_id}",
+            access_token=self.user_token,
+        )
+        self.assertEquals(200, channel.code, channel.json_body)
+        self.assertEqual(channel.json_body["chunk"], [])
+
+        # And for bundled aggregations.
+        channel = self.make_request(
+            "GET",
+            f"/rooms/{room2}/event/{parent_id}",
+            access_token=self.user_token,
+        )
+        self.assertEquals(200, channel.code, channel.json_body)
+        self.assertNotIn("m.relations", channel.json_body["unsigned"])
+
     def test_edit(self):
         """Test that a simple edit works."""