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Avoid putting rejected events in room state (#13723) 

Signed-off-by: Sean Quah <seanq@matrix.org>
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Sean Quah 2022-09-16 12:45:04 +01:00 committed by GitHub
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1
changelog.d/13723.bugfix Normal file
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@ -0,0 +1 @@
Fix a long-standing bug where previously rejected events could end up in room state because they pass auth checks given the current state of the room.

15
synapse/state/v2.py
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@ -577,6 +577,21 @@ async def _iterative_auth_checks(
if ev.rejected_reason is None:
auth_events[key] = event_map[ev_id]
if event.rejected_reason is not None:
# Do not admit previously rejected events into state.
# TODO: This isn't spec compliant. Events that were previously rejected due
# to failing auth checks at their state, but pass auth checks during
# state resolution should be accepted. Synapse does not handle the
# change of rejection status well, so we preserve the previous
# rejection status for now.
#
# Note that events rejected for non-state reasons, such as having the
# wrong auth events, should remain rejected.
#
# https://spec.matrix.org/v1.2/rooms/v9/#rejected-events
# https://github.com/matrix-org/synapse/issues/13797
continue
try:
event_auth.check_state_dependent_auth_rules(
event,

399
tests/handlers/test_federation_event.py
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@ -11,14 +11,23 @@
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from typing import Optional
from unittest import mock
from synapse.api.errors import AuthError
from synapse.api.room_versions import RoomVersion
from synapse.event_auth import (
check_state_dependent_auth_rules,
check_state_independent_auth_rules,
)
from synapse.events import make_event_from_dict
from synapse.events.snapshot import EventContext
from synapse.federation.transport.client import StateRequestResponse
from synapse.logging.context import LoggingContext
from synapse.rest import admin
from synapse.rest.client import login, room
from synapse.state.v2 import _mainline_sort, _reverse_topological_power_sort
from synapse.types import JsonDict
from tests import unittest
from tests.test_utils import event_injection, make_awaitable
@ -449,3 +458,393 @@ class FederationEventHandlerTests(unittest.FederatingHomeserverTestCase):
main_store.get_event(pulled_event.event_id, allow_none=True)
)
self.assertIsNotNone(persisted, "pulled event was not persisted at all")
def test_process_pulled_event_with_rejected_missing_state(self) -> None:
"""Ensure that we correctly handle pulled events with missing state containing a
rejected state event
In this test, we pretend we are processing a "pulled" event (eg, via backfill
or get_missing_events). The pulled event has a prev_event we haven't previously
seen, so the server requests the state at that prev_event. We expect the server
to make a /state request.
We simulate a remote server whose /state includes a rejected kick event for a
local user. Notably, the kick event is rejected only because it cites a rejected
auth event and would otherwise be accepted based on the room state. During state
resolution, we re-run auth and can potentially introduce such rejected events
into the state if we are not careful.
We check that the pulled event is correctly persisted, and that the state
afterwards does not include the rejected kick.
"""
# The DAG we are testing looks like:
#
# ...
# |
# v
# remote admin user joins
# | |
# +-------+ +-------+
# | |
# | rejected power levels
# | from remote server
# | |
# | v
# | rejected kick of local user
# v from remote server
# new power levels |
# | v
# | missing event
# | from remote server
# | |
# +-------+ +-------+
# | |
# v v
# pulled event
# from remote server
#
# (arrows are in the opposite direction to prev_events.)
OTHER_USER = f"@user:{self.OTHER_SERVER_NAME}"
main_store = self.hs.get_datastores().main
# Create the room.
kermit_user_id = self.register_user("kermit", "test")
kermit_tok = self.login("kermit", "test")
room_id = self.helper.create_room_as(
room_creator=kermit_user_id, tok=kermit_tok
)
room_version = self.get_success(main_store.get_room_version(room_id))
# Add another local user to the room. This user is going to be kicked in a
# rejected event.
bert_user_id = self.register_user("bert", "test")
bert_tok = self.login("bert", "test")
self.helper.join(room_id, user=bert_user_id, tok=bert_tok)
# Allow the remote user to kick bert.
# The remote user is going to send a rejected power levels event later on and we
# need state resolution to order it before another power levels event kermit is
# going to send later on. Hence we give both users the same power level, so that
# ties are broken by `origin_server_ts`.
self.helper.send_state(
room_id,
"m.room.power_levels",
{"users": {kermit_user_id: 100, OTHER_USER: 100}},
tok=kermit_tok,
)
# Add the remote user to the room.
other_member_event = self.get_success(
event_injection.inject_member_event(self.hs, room_id, OTHER_USER, "join")
)
initial_state_map = self.get_success(
main_store.get_partial_current_state_ids(room_id)
)
create_event = self.get_success(
main_store.get_event(initial_state_map[("m.room.create", "")])
)
bert_member_event = self.get_success(
main_store.get_event(initial_state_map[("m.room.member", bert_user_id)])
)
power_levels_event = self.get_success(
main_store.get_event(initial_state_map[("m.room.power_levels", "")])
)
# We now need a rejected state event that will fail
# `check_state_independent_auth_rules` but pass
# `check_state_dependent_auth_rules`.
# First, we create a power levels event that we pretend the remote server has
# accepted, but the local homeserver will reject.
next_depth = 100
next_timestamp = other_member_event.origin_server_ts + 100
rejected_power_levels_event = make_event_from_dict(
self.add_hashes_and_signatures_from_other_server(
{
"type": "m.room.power_levels",
"state_key": "",
"room_id": room_id,
"sender": OTHER_USER,
"prev_events": [other_member_event.event_id],
"auth_events": [
initial_state_map[("m.room.create", "")],
initial_state_map[("m.room.power_levels", "")],
# The event will be rejected because of the duplicated auth
# event.
other_member_event.event_id,
other_member_event.event_id,
],
"origin_server_ts": next_timestamp,
"depth": next_depth,
"content": power_levels_event.content,
}
),
room_version,
)
next_depth += 1
next_timestamp += 100
with LoggingContext("send_rejected_power_levels_event"):
self.get_success(
self.hs.get_federation_event_handler()._process_pulled_event(
self.OTHER_SERVER_NAME,
rejected_power_levels_event,
backfilled=False,
)
)
self.assertEqual(
self.get_success(
main_store.get_rejection_reason(
rejected_power_levels_event.event_id
)
),
"auth_error",
)
# Then we create a kick event for a local user that cites the rejected power
# levels event in its auth events. The kick event will be rejected solely
# because of the rejected auth event and would otherwise be accepted.
rejected_kick_event = make_event_from_dict(
self.add_hashes_and_signatures_from_other_server(
{
"type": "m.room.member",
"state_key": bert_user_id,
"room_id": room_id,
"sender": OTHER_USER,
"prev_events": [rejected_power_levels_event.event_id],
"auth_events": [
initial_state_map[("m.room.create", "")],
rejected_power_levels_event.event_id,
initial_state_map[("m.room.member", bert_user_id)],
initial_state_map[("m.room.member", OTHER_USER)],
],
"origin_server_ts": next_timestamp,
"depth": next_depth,
"content": {"membership": "leave"},
}
),
room_version,
)
next_depth += 1
next_timestamp += 100
# The kick event must fail the state-independent auth rules, but pass the
# state-dependent auth rules, so that it has a chance of making it through state
# resolution.
self.get_failure(
check_state_independent_auth_rules(main_store, rejected_kick_event),
AuthError,
)
check_state_dependent_auth_rules(
rejected_kick_event,
[create_event, power_levels_event, other_member_event, bert_member_event],
)
# The kick event must also win over the original member event during state
# resolution.
self.assertEqual(
self.get_success(
_mainline_sort(
self.clock,
room_id,
event_ids=[
bert_member_event.event_id,
rejected_kick_event.event_id,
],
resolved_power_event_id=power_levels_event.event_id,
event_map={
bert_member_event.event_id: bert_member_event,
rejected_kick_event.event_id: rejected_kick_event,
},
state_res_store=main_store,
)
),
[bert_member_event.event_id, rejected_kick_event.event_id],
"The rejected kick event will not be applied after bert's join event "
"during state resolution. The test setup is incorrect.",
)
with LoggingContext("send_rejected_kick_event"):
self.get_success(
self.hs.get_federation_event_handler()._process_pulled_event(
self.OTHER_SERVER_NAME, rejected_kick_event, backfilled=False
)
)
self.assertEqual(
self.get_success(
main_store.get_rejection_reason(rejected_kick_event.event_id)
),
"auth_error",
)
# We need another power levels event which will win over the rejected one during
# state resolution, otherwise we hit other issues where we end up with rejected
# a power levels event during state resolution.
self.reactor.advance(100) # ensure the `origin_server_ts` is larger
new_power_levels_event = self.get_success(
main_store.get_event(
self.helper.send_state(
room_id,
"m.room.power_levels",
{"users": {kermit_user_id: 100, OTHER_USER: 100, bert_user_id: 1}},
tok=kermit_tok,
)["event_id"]
)
)
self.assertEqual(
self.get_success(
_reverse_topological_power_sort(
self.clock,
room_id,
event_ids=[
new_power_levels_event.event_id,
rejected_power_levels_event.event_id,
],
event_map={},
state_res_store=main_store,
full_conflicted_set=set(),
)
),
[rejected_power_levels_event.event_id, new_power_levels_event.event_id],
"The power levels events will not have the desired ordering during state "
"resolution. The test setup is incorrect.",
)
# Create a missing event, so that the local homeserver has to do a `/state` or
# `/state_ids` request to pull state from the remote homeserver.
missing_event = make_event_from_dict(
self.add_hashes_and_signatures_from_other_server(
{
"type": "m.room.message",
"room_id": room_id,
"sender": OTHER_USER,
"prev_events": [rejected_kick_event.event_id],
"auth_events": [
initial_state_map[("m.room.create", "")],
initial_state_map[("m.room.power_levels", "")],
initial_state_map[("m.room.member", OTHER_USER)],
],
"origin_server_ts": next_timestamp,
"depth": next_depth,
"content": {"msgtype": "m.text", "body": "foo"},
}
),
room_version,
)
next_depth += 1
next_timestamp += 100
# The pulled event has two prev events, one of which is missing. We will make a
# `/state` or `/state_ids` request to the remote homeserver to ask it for the
# state before the missing prev event.
pulled_event = make_event_from_dict(
self.add_hashes_and_signatures_from_other_server(
{
"type": "m.room.message",
"room_id": room_id,
"sender": OTHER_USER,
"prev_events": [
new_power_levels_event.event_id,
missing_event.event_id,
],
"auth_events": [
initial_state_map[("m.room.create", "")],
new_power_levels_event.event_id,
initial_state_map[("m.room.member", OTHER_USER)],
],
"origin_server_ts": next_timestamp,
"depth": next_depth,
"content": {"msgtype": "m.text", "body": "bar"},
}
),
room_version,
)
next_depth += 1
next_timestamp += 100
# Prepare the response for the `/state` or `/state_ids` request.
# The remote server believes bert has been kicked, while the local server does
# not.
state_before_missing_event = self.get_success(
main_store.get_events_as_list(initial_state_map.values())
)
state_before_missing_event = [
event
for event in state_before_missing_event
if event.event_id != bert_member_event.event_id
]
state_before_missing_event.append(rejected_kick_event)
# We have to bump the clock a bit, to keep the retry logic in
# `FederationClient.get_pdu` happy
self.reactor.advance(60000)
with LoggingContext("send_pulled_event"):
async def get_event(
destination: str, event_id: str, timeout: Optional[int] = None
) -> JsonDict:
self.assertEqual(destination, self.OTHER_SERVER_NAME)
self.assertEqual(event_id, missing_event.event_id)
return {"pdus": [missing_event.get_pdu_json()]}
async def get_room_state_ids(
destination: str, room_id: str, event_id: str
) -> JsonDict:
self.assertEqual(destination, self.OTHER_SERVER_NAME)
self.assertEqual(event_id, missing_event.event_id)
return {
"pdu_ids": [event.event_id for event in state_before_missing_event],
"auth_chain_ids": [],
}
async def get_room_state(
room_version: RoomVersion, destination: str, room_id: str, event_id: str
) -> StateRequestResponse:
self.assertEqual(destination, self.OTHER_SERVER_NAME)
self.assertEqual(event_id, missing_event.event_id)
return StateRequestResponse(
state=state_before_missing_event,
auth_events=[],
)
self.mock_federation_transport_client.get_event.side_effect = get_event
self.mock_federation_transport_client.get_room_state_ids.side_effect = (
get_room_state_ids
)
self.mock_federation_transport_client.get_room_state.side_effect = (
get_room_state
)
self.get_success(
self.hs.get_federation_event_handler()._process_pulled_event(
self.OTHER_SERVER_NAME, pulled_event, backfilled=False
)
)
self.assertIsNone(
self.get_success(
main_store.get_rejection_reason(pulled_event.event_id)
),
"Pulled event was unexpectedly rejected, likely due to a problem with "
"the test setup.",
)
self.assertEqual(
{pulled_event.event_id},
self.get_success(
main_store.have_events_in_timeline([pulled_event.event_id])
),
"Pulled event was not persisted, likely due to a problem with the test "
"setup.",
)
# We must not accept rejected events into the room state, so we expect bert
# to not be kicked, even if the remote server believes so.
new_state_map = self.get_success(
main_store.get_partial_current_state_ids(room_id)
)
self.assertEqual(
new_state_map[("m.room.member", bert_user_id)],
bert_member_event.event_id,
"Rejected kick event unexpectedly became part of room state.",
)