Track when the pulled event signature fails

synapse/federation/federation_base.py

@@ -13,7 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import logging
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, Awaitable, Callable, Optional
 
 from synapse.api.constants import MAX_DEPTH, EventContentFields, EventTypes, Membership
 from synapse.api.errors import Codes, SynapseError
@@ -58,7 +58,12 @@ def __init__(self, hs: "HomeServer"):
 
     @trace
     async def _check_sigs_and_hash(
-        self, room_version: RoomVersion, pdu: EventBase
+        self,
+        room_version: RoomVersion,
+        pdu: EventBase,
+        record_failure_callback: Optional[
+            Callable[[EventBase, str], Awaitable[None]]
+        ] = None,
     ) -> EventBase:
         """Checks that event is correctly signed by the sending server.
 
@@ -83,9 +88,8 @@ async def _check_sigs_and_hash(
         try:
             await _check_sigs_on_pdu(self.keyring, room_version, pdu)
         except Exception as exc:
-            await self.store.record_event_failed_pull_attempt(
-                pdu.room_id, pdu.event_id, str(exc)
-            )
+            if record_failure_callback:
+                await record_failure_callback(pdu, str(exc))
             raise exc
 
         if not check_event_content_hash(pdu):
@@ -122,9 +126,10 @@ async def _check_sigs_and_hash(
                         "event_id": pdu.event_id,
                     }
                 )
-                await self.store.record_event_failed_pull_attempt(
-                    pdu.room_id, pdu.event_id, "Event content has been tampered with"
-                )
+                if record_failure_callback:
+                    await record_failure_callback(
+                        pdu, "Event content has been tampered with"
+                    )
             return redacted_event
 
         spam_check = await self.spam_checker.check_event_for_spam(pdu)

synapse/federation/federation_client.py

@@ -278,7 +278,7 @@ async def backfill(
         pdus = [event_from_pdu_json(p, room_version) for p in transaction_data_pdus]
 
         # Check signatures and hash of pdus, removing any from the list that fail checks
-        pdus[:] = await self._check_sigs_and_hash_and_fetch(
+        pdus[:] = await self._check_sigs_and_hash_for_pulled_events_and_fetch(
             dest, pdus, room_version=room_version
         )
 
@@ -547,24 +547,28 @@ async def get_room_state(
             len(auth_event_map),
         )
 
-        valid_auth_events = await self._check_sigs_and_hash_and_fetch(
+        valid_auth_events = await self._check_sigs_and_hash_for_pulled_events_and_fetch(
             destination, auth_event_map.values(), room_version
         )
 
-        valid_state_events = await self._check_sigs_and_hash_and_fetch(
-            destination, state_event_map.values(), room_version
+        valid_state_events = (
+            await self._check_sigs_and_hash_for_pulled_events_and_fetch(
+                destination, state_event_map.values(), room_version
+            )
         )
 
         return valid_state_events, valid_auth_events
 
     @trace
-    async def _check_sigs_and_hash_and_fetch(
+    async def _check_sigs_and_hash_for_pulled_events_and_fetch(
         self,
         origin: str,
         pdus: Collection[EventBase],
         room_version: RoomVersion,
     ) -> List[EventBase]:
-        """Checks the signatures and hashes of a list of events.
+        """
+        Checks the signatures and hashes of a list of pulled events we got from
+        federation and records any signature failures as failed pull attempts.
 
         If a PDU fails its signature check then we check if we have it in
         the database, and if not then request it from the sender's server (if that
@@ -597,11 +601,17 @@ async def _check_sigs_and_hash_and_fetch(
 
         valid_pdus: List[EventBase] = []
 
+        async def _record_failure_callback(event: EventBase, cause: str) -> None:
+            await self.store.record_event_failed_pull_attempt(
+                event.room_id, event.event_id, cause
+            )
+
         async def _execute(pdu: EventBase) -> None:
             valid_pdu = await self._check_sigs_and_hash_and_fetch_one(
                 pdu=pdu,
                 origin=origin,
                 room_version=room_version,
+                record_failure_callback=_record_failure_callback,
             )
 
             if valid_pdu:
@@ -618,6 +628,9 @@ async def _check_sigs_and_hash_and_fetch_one(
         pdu: EventBase,
         origin: str,
         room_version: RoomVersion,
+        record_failure_callback: Optional[
+            Callable[[EventBase, str], Awaitable[None]]
+        ] = None,
     ) -> Optional[EventBase]:
         """Takes a PDU and checks its signatures and hashes.
 
@@ -694,7 +707,7 @@ async def get_event_auth(
 
         auth_chain = [event_from_pdu_json(p, room_version) for p in res["auth_chain"]]
 
-        signed_auth = await self._check_sigs_and_hash_and_fetch(
+        signed_auth = await self._check_sigs_and_hash_for_pulled_events_and_fetch(
             destination, auth_chain, room_version=room_version
         )
 
@@ -1401,7 +1414,7 @@ async def get_missing_events(
                 event_from_pdu_json(e, room_version) for e in content.get("events", [])
             ]
 
-            signed_events = await self._check_sigs_and_hash_and_fetch(
+            signed_events = await self._check_sigs_and_hash_for_pulled_events_and_fetch(
                 destination, events, room_version=room_version
             )
         except HttpResponseException as e:

tests/test_federation.py

@@ -86,8 +86,8 @@ async def _check_event_auth(origin, event, context):
 
         federation_event_handler._check_event_auth = _check_event_auth
         self.client = self.homeserver.get_federation_client()
-        self.client._check_sigs_and_hash_and_fetch = lambda dest, pdus, **k: succeed(
-            pdus
+        self.client._check_sigs_and_hash_for_pulled_events_and_fetch = (
+            lambda dest, pdus, **k: succeed(pdus)
         )
 
         # Send the join, it should return None (which is not an error)