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Track when the pulled event signature fails (#13815)

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Because we're doing the recording in `_check_sigs_and_hash_for_pulled_events_and_fetch` (previously named `_check_sigs_and_hash_and_fetch`), this means we will track signature failures for `backfill`, `get_room_state`, `get_event_auth`, and `get_missing_events` (all pulled event scenarios). And we also record signature failures from `get_pdu`.

Part of https://github.com/matrix-org/synapse/issues/13700

Part of https://github.com/matrix-org/synapse/issues/13676 and https://github.com/matrix-org/synapse/issues/13356

This PR will be especially important for https://github.com/matrix-org/synapse/pull/13816 so we can avoid the costly `_get_state_ids_after_missing_prev_event` down the line when `/messages` calls backfill.
This commit is contained in:
Eric Eastwood 2022-10-03 14:53:29 -05:00 committed by GitHub
parent 92ae90aca2
commit 70a4317692
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GPG key ID: 4AEE18F83AFDEB23
5 changed files with 140 additions and 15 deletions
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1
changelog.d/13815.feature Normal file
View file

@ -0,0 +1 @@
Keep track when an event pulled over federation fails its signature check so we can intelligently back-off in the future.

25
synapse/federation/federation_base.py
View file

@ -13,7 +13,7 @@
# See the License for the specific language governing permissions and
# limitations under the License.
import logging
from typing import TYPE_CHECKING
from typing import TYPE_CHECKING, Awaitable, Callable, Optional
from synapse.api.constants import MAX_DEPTH, EventContentFields, EventTypes, Membership
from synapse.api.errors import Codes, SynapseError
@ -58,7 +58,12 @@ class FederationBase:
@trace
async def _check_sigs_and_hash(
self, room_version: RoomVersion, pdu: EventBase
self,
room_version: RoomVersion,
pdu: EventBase,
record_failure_callback: Optional[
Callable[[EventBase, str], Awaitable[None]]
] = None,
) -> EventBase:
"""Checks that event is correctly signed by the sending server.
@ -70,6 +75,11 @@ class FederationBase:
Args:
room_version: The room version of the PDU
pdu: the event to be checked
record_failure_callback: A callback to run whenever the given event
fails signature or hash checks. This includes exceptions
that would be normally be thrown/raised but also things like
checking for event tampering where we just return the redacted
event.
Returns:
* the original event if the checks pass
@ -80,7 +90,12 @@ class FederationBase:
InvalidEventSignatureError if the signature check failed. Nothing
will be logged in this case.
"""
await _check_sigs_on_pdu(self.keyring, room_version, pdu)
try:
await _check_sigs_on_pdu(self.keyring, room_version, pdu)
except InvalidEventSignatureError as exc:
if record_failure_callback:
await record_failure_callback(pdu, str(exc))
raise exc
if not check_event_content_hash(pdu):
# let's try to distinguish between failures because the event was
@ -116,6 +131,10 @@ class FederationBase:
"event_id": pdu.event_id,
}
)
if record_failure_callback:
await record_failure_callback(
pdu, "Event content has been tampered with"
)
return redacted_event
spam_check = await self.spam_checker.check_event_for_spam(pdu)

50
synapse/federation/federation_client.py
View file

@ -278,7 +278,7 @@ class FederationClient(FederationBase):
pdus = [event_from_pdu_json(p, room_version) for p in transaction_data_pdus]
# Check signatures and hash of pdus, removing any from the list that fail checks
pdus[:] = await self._check_sigs_and_hash_and_fetch(
pdus[:] = await self._check_sigs_and_hash_for_pulled_events_and_fetch(
dest, pdus, room_version=room_version
)
@ -328,7 +328,17 @@ class FederationClient(FederationBase):
# Check signatures are correct.
try:
signed_pdu = await self._check_sigs_and_hash(room_version, pdu)
async def _record_failure_callback(
event: EventBase, cause: str
) -> None:
await self.store.record_event_failed_pull_attempt(
event.room_id, event.event_id, cause
)
signed_pdu = await self._check_sigs_and_hash(
room_version, pdu, _record_failure_callback
)
except InvalidEventSignatureError as e:
errmsg = f"event id {pdu.event_id}: {e}"
logger.warning("%s", errmsg)
@ -547,24 +557,28 @@ class FederationClient(FederationBase):
len(auth_event_map),
)
valid_auth_events = await self._check_sigs_and_hash_and_fetch(
valid_auth_events = await self._check_sigs_and_hash_for_pulled_events_and_fetch(
destination, auth_event_map.values(), room_version
)
valid_state_events = await self._check_sigs_and_hash_and_fetch(
destination, state_event_map.values(), room_version
valid_state_events = (
await self._check_sigs_and_hash_for_pulled_events_and_fetch(
destination, state_event_map.values(), room_version
)
)
return valid_state_events, valid_auth_events
@trace
async def _check_sigs_and_hash_and_fetch(
async def _check_sigs_and_hash_for_pulled_events_and_fetch(
self,
origin: str,
pdus: Collection[EventBase],
room_version: RoomVersion,
) -> List[EventBase]:
"""Checks the signatures and hashes of a list of events.
"""
Checks the signatures and hashes of a list of pulled events we got from
federation and records any signature failures as failed pull attempts.
If a PDU fails its signature check then we check if we have it in
the database, and if not then request it from the sender's server (if that
@ -597,11 +611,17 @@ class FederationClient(FederationBase):
valid_pdus: List[EventBase] = []
async def _record_failure_callback(event: EventBase, cause: str) -> None:
await self.store.record_event_failed_pull_attempt(
event.room_id, event.event_id, cause
)
async def _execute(pdu: EventBase) -> None:
valid_pdu = await self._check_sigs_and_hash_and_fetch_one(
pdu=pdu,
origin=origin,
room_version=room_version,
record_failure_callback=_record_failure_callback,
)
if valid_pdu:
@ -618,6 +638,9 @@ class FederationClient(FederationBase):
pdu: EventBase,
origin: str,
room_version: RoomVersion,
record_failure_callback: Optional[
Callable[[EventBase, str], Awaitable[None]]
] = None,
) -> Optional[EventBase]:
"""Takes a PDU and checks its signatures and hashes.
@ -634,6 +657,11 @@ class FederationClient(FederationBase):
origin
pdu
room_version
record_failure_callback: A callback to run whenever the given event
fails signature or hash checks. This includes exceptions
that would be normally be thrown/raised but also things like
checking for event tampering where we just return the redacted
event.
Returns:
The PDU (possibly redacted) if it has valid signatures and hashes.
@ -641,7 +669,9 @@ class FederationClient(FederationBase):
"""
try:
return await self._check_sigs_and_hash(room_version, pdu)
return await self._check_sigs_and_hash(
room_version, pdu, record_failure_callback
)
except InvalidEventSignatureError as e:
logger.warning(
"Signature on retrieved event %s was invalid (%s). "
@ -694,7 +724,7 @@ class FederationClient(FederationBase):
auth_chain = [event_from_pdu_json(p, room_version) for p in res["auth_chain"]]
signed_auth = await self._check_sigs_and_hash_and_fetch(
signed_auth = await self._check_sigs_and_hash_for_pulled_events_and_fetch(
destination, auth_chain, room_version=room_version
)
@ -1401,7 +1431,7 @@ class FederationClient(FederationBase):
event_from_pdu_json(e, room_version) for e in content.get("events", [])
]
signed_events = await self._check_sigs_and_hash_and_fetch(
signed_events = await self._check_sigs_and_hash_for_pulled_events_and_fetch(
destination, events, room_version=room_version
)
except HttpResponseException as e:

75
tests/federation/test_federation_client.py
View file

@ -23,14 +23,23 @@ from twisted.test.proto_helpers import MemoryReactor
from synapse.api.room_versions import RoomVersions
from synapse.events import EventBase
from synapse.rest import admin
from synapse.rest.client import login, room
from synapse.server import HomeServer
from synapse.types import JsonDict
from synapse.util import Clock
from tests.test_utils import event_injection
from tests.unittest import FederatingHomeserverTestCase
class FederationClientTest(FederatingHomeserverTestCase):
servlets = [
admin.register_servlets,
room.register_servlets,
login.register_servlets,
]
def prepare(self, reactor: MemoryReactor, clock: Clock, homeserver: HomeServer):
super().prepare(reactor, clock, homeserver)
@ -231,6 +240,72 @@ class FederationClientTest(FederatingHomeserverTestCase):
return remote_pdu
def test_backfill_invalid_signature_records_failed_pull_attempts(
self,
) -> None:
"""
Test to make sure that events from /backfill with invalid signatures get
recorded as failed pull attempts.
"""
OTHER_USER = f"@user:{self.OTHER_SERVER_NAME}"
main_store = self.hs.get_datastores().main
# Create the room
user_id = self.register_user("kermit", "test")
tok = self.login("kermit", "test")
room_id = self.helper.create_room_as(room_creator=user_id, tok=tok)
# We purposely don't run `add_hashes_and_signatures_from_other_server`
# over this because we want the signature check to fail.
pulled_event, _ = self.get_success(
event_injection.create_event(
self.hs,
room_id=room_id,
sender=OTHER_USER,
type="test_event_type",
content={"body": "garply"},
)
)
# We expect an outbound request to /backfill, so stub that out
self._mock_agent.request.side_effect = lambda *args, **kwargs: defer.succeed(
_mock_response(
{
"origin": "yet.another.server",
"origin_server_ts": 900,
# Mimic the other server returning our new `pulled_event`
"pdus": [pulled_event.get_pdu_json()],
}
)
)
self.get_success(
self.hs.get_federation_client().backfill(
# We use "yet.another.server" instead of
# `self.OTHER_SERVER_NAME` because we want to see the behavior
# from `_check_sigs_and_hash_and_fetch_one` where it tries to
# fetch the PDU again from the origin server if the signature
# fails. Just want to make sure that the failure is counted from
# both code paths.
dest="yet.another.server",
room_id=room_id,
limit=1,
extremities=[pulled_event.event_id],
),
)
# Make sure our failed pull attempt was recorded
backfill_num_attempts = self.get_success(
main_store.db_pool.simple_select_one_onecol(
table="event_failed_pull_attempts",
keyvalues={"event_id": pulled_event.event_id},
retcol="num_attempts",
)
)
# This is 2 because it failed once from `self.OTHER_SERVER_NAME` and the
# other from "yet.another.server"
self.assertEqual(backfill_num_attempts, 2)
def _mock_response(resp: JsonDict):
body = json.dumps(resp).encode("utf-8")

4
tests/test_federation.py
View file

@ -86,8 +86,8 @@ class MessageAcceptTests(unittest.HomeserverTestCase):
federation_event_handler._check_event_auth = _check_event_auth
self.client = self.homeserver.get_federation_client()
self.client._check_sigs_and_hash_and_fetch = lambda dest, pdus, **k: succeed(
pdus
self.client._check_sigs_and_hash_for_pulled_events_and_fetch = (
lambda dest, pdus, **k: succeed(pdus)
)
# Send the join, it should return None (which is not an error)