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Check the room_id of events when fetching room state/auth (#6524)

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When we request the state/auth_events to populate a backwards extremity (on
backfill or in the case of missing events in a transaction push), we should
check that the returned events are in the right room rather than blindly using
them in the room state or auth chain.

Given that _get_events_from_store_or_dest takes a room_id, it seems clear that
it should be sanity-checking the room_id of the requested events, so let's do
it there.
This commit is contained in:
Richard van der Hoff 2019-12-12 12:57:45 +00:00 committed by GitHub
parent b8e4b39b69
commit 25f1244329
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2 changed files with 55 additions and 25 deletions
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2
changelog.d/6524.misc Normal file
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@ -0,0 +1,2 @@
Improve sanity-checking when receiving events over federation.

78
synapse/handlers/federation.py
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@ -637,6 +637,10 @@ class FederationHandler(BaseHandler):
room_id
event_ids
If we fail to fetch any of the events, a warning will be logged, and the event
will be omitted from the result. Likewise, any events which turn out not to
be in the given room.
Returns:
map from event_id to event
"""
@ -644,35 +648,59 @@ class FederationHandler(BaseHandler):
missing_events = set(event_ids) - fetched_events.keys()
if not missing_events:
return fetched_events
if missing_events:
logger.debug(
"Fetching unknown state/auth events %s for room %s",
missing_events,
room_id,
)
logger.debug(
"Fetching unknown state/auth events %s for room %s",
missing_events,
event_ids,
room_version = await self.store.get_room_version(room_id)
# XXX 20 requests at once? really?
for batch in batch_iter(missing_events, 20):
deferreds = [
run_in_background(
self.federation_client.get_pdu,
destinations=[destination],
event_id=e_id,
room_version=room_version,
)
for e_id in batch
]
res = await make_deferred_yieldable(
defer.DeferredList(deferreds, consumeErrors=True)
)
for success, result in res:
if success and result:
fetched_events[result.event_id] = result
# check for events which were in the wrong room.
#
# this can happen if a remote server claims that the state or
# auth_events at an event in room A are actually events in room B
bad_events = list(
(event_id, event.room_id)
for event_id, event in fetched_events.items()
if event.room_id != room_id
)
room_version = await self.store.get_room_version(room_id)
# XXX 20 requests at once? really?
for batch in batch_iter(missing_events, 20):
deferreds = [
run_in_background(
self.federation_client.get_pdu,
destinations=[destination],
event_id=e_id,
room_version=room_version,
)
for e_id in batch
]
res = await make_deferred_yieldable(
defer.DeferredList(deferreds, consumeErrors=True)
for bad_event_id, bad_room_id in bad_events:
# This is a bogus situation, but since we may only discover it a long time
# after it happened, we try our best to carry on, by just omitting the
# bad events from the returned auth/state set.
logger.warning(
"Remote server %s claims event %s in room %s is an auth/state "
"event in room %s",
destination,
bad_event_id,
bad_room_id,
room_id,
)
for success, result in res:
if success and result:
fetched_events[result.event_id] = result
del fetched_events[bad_event_id]
return fetched_events