Fix bug in device list caching when remote users leave rooms (#13749)

When a remote user leaves the last room shared with the homeserver, we
have to mark their device list as unsubscribed, otherwise we would hold
on to a stale device list in our cache. Crucially, the device list would
remain cached even after the remote user rejoined the room, which could
lead to E2EE failures until the next change to the remote user's device
list.

Fixes #13651.

Signed-off-by: Sean Quah <seanq@matrix.org>
This commit is contained in:
Sean Quah 2022-09-14 10:42:57 +01:00 committed by GitHub
parent 21687ec189
commit c73774467e
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GPG key ID: 4AEE18F83AFDEB23
5 changed files with 51 additions and 15 deletions

1
changelog.d/13749.bugfix Normal file
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@ -0,0 +1 @@
Fix a long standing bug where device lists would remain cached when remote users left and rejoined the last room shared with the local homeserver.

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@ -45,7 +45,6 @@ from synapse.types import (
JsonDict,
StreamKeyType,
StreamToken,
UserID,
get_domain_from_id,
get_verify_key_from_cross_signing_key,
)
@ -324,8 +323,6 @@ class DeviceHandler(DeviceWorkerHandler):
self.device_list_updater.incoming_device_list_update,
)
hs.get_distributor().observe("user_left_room", self.user_left_room)
# Whether `_handle_new_device_update_async` is currently processing.
self._handle_new_device_update_is_processing = False
@ -569,14 +566,6 @@ class DeviceHandler(DeviceWorkerHandler):
StreamKeyType.DEVICE_LIST, position, users=[from_user_id]
)
async def user_left_room(self, user: UserID, room_id: str) -> None:
user_id = user.to_string()
room_ids = await self.store.get_rooms_for_user(user_id)
if not room_ids:
# We no longer share rooms with this user, so we'll no longer
# receive device updates. Mark this in DB.
await self.store.mark_remote_user_device_list_as_unsubscribed(user_id)
async def store_dehydrated_device(
self,
user_id: str,

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@ -175,6 +175,32 @@ class E2eKeysHandler:
user_ids_not_in_cache,
remote_results,
) = await self.store.get_user_devices_from_cache(query_list)
# Check that the homeserver still shares a room with all cached users.
# Note that this check may be slightly racy when a remote user leaves a
# room after we have fetched their cached device list. In the worst case
# we will do extra federation queries for devices that we had cached.
cached_users = set(remote_results.keys())
valid_cached_users = (
await self.store.get_users_server_still_shares_room_with(
remote_results.keys()
)
)
invalid_cached_users = cached_users - valid_cached_users
if invalid_cached_users:
# Fix up results. If we get here, there is either a bug in device
# list tracking, or we hit the race mentioned above.
user_ids_not_in_cache.update(invalid_cached_users)
for invalid_user_id in invalid_cached_users:
remote_results.pop(invalid_user_id)
# This log message may be removed if it turns out it's almost
# entirely triggered by races.
logger.error(
"Devices for %s were cached, but the server no longer shares "
"any rooms with them. The cached device lists are stale.",
invalid_cached_users,
)
for user_id, devices in remote_results.items():
user_devices = results.setdefault(user_id, {})
for device_id, device in devices.items():

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@ -598,9 +598,9 @@ class EventsPersistenceStorageController:
# room
state_delta_for_room: Dict[str, DeltaState] = {}
# Set of remote users which were in rooms the server has left. We
# should check if we still share any rooms and if not we mark their
# device lists as stale.
# Set of remote users which were in rooms the server has left or who may
# have left rooms the server is in. We should check if we still share any
# rooms and if not we mark their device lists as stale.
potentially_left_users: Set[str] = set()
if not backfilled:
@ -725,6 +725,20 @@ class EventsPersistenceStorageController:
current_state = {}
delta.no_longer_in_room = True
# Add all remote users that might have left rooms.
potentially_left_users.update(
user_id
for event_type, user_id in delta.to_delete
if event_type == EventTypes.Member
and not self.is_mine_id(user_id)
)
potentially_left_users.update(
user_id
for event_type, user_id in delta.to_insert.keys()
if event_type == EventTypes.Member
and not self.is_mine_id(user_id)
)
state_delta_for_room[room_id] = delta
await self.persist_events_store._persist_events_and_state_updates(

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@ -891,6 +891,12 @@ class E2eKeysHandlerTestCase(unittest.HomeserverTestCase):
new_callable=mock.MagicMock,
return_value=make_awaitable(["some_room_id"]),
)
mock_get_users = mock.patch.object(
self.store,
"get_users_server_still_shares_room_with",
new_callable=mock.MagicMock,
return_value=make_awaitable({remote_user_id}),
)
mock_request = mock.patch.object(
self.hs.get_federation_client(),
"query_user_devices",
@ -898,7 +904,7 @@ class E2eKeysHandlerTestCase(unittest.HomeserverTestCase):
return_value=make_awaitable(response_body),
)
with mock_get_rooms, mock_request as mocked_federation_request:
with mock_get_rooms, mock_get_users, mock_request as mocked_federation_request:
# Make the first query and sanity check it succeeds.
response_1 = self.get_success(
e2e_handler.query_devices(