From 5d051b2da29cee2673ca039b64da6cf8ba00f335 Mon Sep 17 00:00:00 2001
From: Richard van der Hoff <richard@matrix.org>
Date: Mon, 20 Sep 2021 18:20:17 +0100
Subject: [PATCH] Stop trying to auth/persist events whose auth events we do
not have.
---
changelog.d/10907.bugfix | 1 +
synapse/handlers/federation_event.py | 24 ++++++++++++++++--------
2 files changed, 17 insertions(+), 8 deletions(-)
create mode 100644 changelog.d/10907.bugfix
diff --git a/changelog.d/10907.bugfix b/changelog.d/10907.bugfix
new file mode 100644
index 000000000000..601b341f9fa6
--- /dev/null
+++ b/changelog.d/10907.bugfix
@@ -0,0 +1 @@
+Fix a long-standing bug which could cause events pulled over federation to be incorrectly rejected.
diff --git a/synapse/handlers/federation_event.py b/synapse/handlers/federation_event.py
index 8fd9e51044d6..01fd84112252 100644
--- a/synapse/handlers/federation_event.py
+++ b/synapse/handlers/federation_event.py
@@ -1194,10 +1194,17 @@ async def prep(event: EventBase) -> Optional[Tuple[EventBase, EventContext]]:
auth = {}
for auth_event_id in event.auth_event_ids():
ae = persisted_events.get(auth_event_id)
- if ae:
- auth[(ae.type, ae.state_key)] = ae
- else:
- logger.info("Missing auth event %s", auth_event_id)
+ if not ae:
+ logger.warning(
+ "Event %s relies on auth_event %s, which could not be found.",
+ event,
+ auth_event_id,
+ )
+ # the fact we can't find the auth event doesn't mean it doesn't
+ # exist, which means it is premature to reject `event`. Instead we
+ # just ignore it for now.
+ return None
+ auth[(ae.type, ae.state_key)] = ae
context = EventContext.for_outlier()
context = await self._check_event_auth(
@@ -1208,8 +1215,10 @@ async def prep(event: EventBase) -> Optional[Tuple[EventBase, EventContext]]:
)
return event, context
- events_to_persist = await yieldable_gather_results(prep, fetched_events)
- await self.persist_events_and_notify(room_id, events_to_persist)
+ events_to_persist = (
+ x for x in await yieldable_gather_results(prep, fetched_events) if x
+ )
+ await self.persist_events_and_notify(room_id, tuple(events_to_persist))
async def _check_event_auth(
self,
@@ -1235,8 +1244,7 @@ async def _check_event_auth(
claimed_auth_event_map:
A map of (type, state_key) => event for the event's claimed auth_events.
- Possibly incomplete, and possibly including events that are not yet
- persisted, or authed, or in the right room.
+ Possibly including events that were rejected, or are in the wrong room.
Only populated when populating outliers.