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Persist auth events before the events that rely on them (#10771)

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If we're persisting an event E which has auth_events A1, A2, then we ought to make sure that we correctly auth
and persist A1 and A2, before we blindly accept E.

This PR does part of that - it persists the auth events first - but it does not fully solve the problem, because we
still don't check that the auth events weren't rejected.
This commit is contained in:
Richard van der Hoff 2021-09-08 10:37:50 +01:00 committed by GitHub
parent 857b000996
commit 5724883ac2
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2 changed files with 66 additions and 36 deletions
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1
changelog.d/10771.misc Normal file
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@ -0,0 +1 @@
Clean up some of the federation event authentication code for clarity.

101
synapse/handlers/federation_event.py
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@ -818,7 +818,7 @@ class FederationEventHandler:
missing_events = missing_desired_events | missing_auth_events
logger.debug("Fetching %i events from remote", len(missing_events))
await self._get_events_and_persist(
destination=destination, room_id=room_id, events=missing_events
destination=destination, room_id=room_id, event_ids=missing_events
)
# we need to make sure we re-load from the database to get the rejected
@ -1085,12 +1085,12 @@ class FederationEventHandler:
)
async def _get_events_and_persist(
self, destination: str, room_id: str, events: Iterable[str]
self, destination: str, room_id: str, event_ids: Collection[str]
) -> None:
"""Fetch the given events from a server, and persist them as outliers.
This function *does not* recursively get missing auth events of the
newly fetched events. Callers must include in the `events` argument
newly fetched events. Callers must include in the `event_ids` argument
any missing events from the auth chain.
Logs a warning if we can't find the given event.
@ -1127,28 +1127,78 @@ class FederationEventHandler:
e,
)
await concurrently_execute(get_event, events, 5)
await concurrently_execute(get_event, event_ids, 5)
logger.info("Fetched %i events of %i requested", len(event_map), len(event_ids))
# Make a map of auth events for each event. We do this after fetching
# all the events as some of the events' auth events will be in the list
# of requested events.
# we now need to auth the events in an order which ensures that each event's
# auth_events are authed before the event itself.
#
# XXX: it might be possible to kick this process off in parallel with fetching
# the events.
while event_map:
# build a list of events whose auth events are not in the queue.
roots = tuple(
ev
for ev in event_map.values()
if not any(aid in event_map for aid in ev.auth_event_ids())
)
auth_events = [
aid
for event in event_map.values()
for aid in event.auth_event_ids()
if aid not in event_map
]
if not roots:
# if *none* of the remaining events are ready, that means
# we have a loop. This either means a bug in our logic, or that
# somebody has managed to create a loop (which requires finding a
# hash collision in room v2 and later).
logger.warning(
"Loop found in auth events while fetching missing state/auth "
"events: %s",
shortstr(event_map.keys()),
)
return
logger.info(
"Persisting %i of %i remaining events", len(roots), len(event_map)
)
await self._auth_and_persist_fetched_events(destination, room_id, roots)
for ev in roots:
del event_map[ev.event_id]
async def _auth_and_persist_fetched_events(
self, origin: str, room_id: str, fetched_events: Collection[EventBase]
) -> None:
"""Persist the events fetched by _get_events_and_persist.
The events should not depend on one another, e.g. this should be used to persist
a bunch of outliers, but not a chunk of individual events that depend
on each other for state calculations.
We also assume that all of the auth events for all of the events have already
been persisted.
Notifies about the events where appropriate.
Params:
origin: where the events came from
room_id: the room that the events are meant to be in (though this has
not yet been checked)
event_id: map from event_id -> event for the fetched events
"""
# get all the auth events for all the events in this batch. By now, they should
# have been persisted.
auth_events = {
aid for event in fetched_events for aid in event.auth_event_ids()
}
persisted_events = await self._store.get_events(
auth_events,
allow_rejected=True,
)
event_infos = []
for event in event_map.values():
for event in fetched_events:
auth = {}
for auth_event_id in event.auth_event_ids():
ae = persisted_events.get(auth_event_id) or event_map.get(auth_event_id)
ae = persisted_events.get(auth_event_id)
if ae:
auth[(ae.type, ae.state_key)] = ae
else:
@ -1156,27 +1206,6 @@ class FederationEventHandler:
event_infos.append(_NewEventInfo(event, auth))
if event_infos:
await self._auth_and_persist_events(
destination,
room_id,
event_infos,
)
async def _auth_and_persist_events(
self,
origin: str,
room_id: str,
event_infos: Collection[_NewEventInfo],
) -> None:
"""Creates the appropriate contexts and persists events. The events
should not depend on one another, e.g. this should be used to persist
a bunch of outliers, but not a chunk of individual events that depend
on each other for state calculations.
Notifies about the events where appropriate.
"""
if not event_infos:
return