Merge pull request #3118 from matrix-org/rav/reject_prev_events

Reject events which have lots of prev_events
This commit is contained in:
Richard van der Hoff 2018-04-23 17:51:38 +01:00 committed by GitHub
commit 77ebef9d43
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2 changed files with 94 additions and 9 deletions

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@ -1,5 +1,6 @@
# -*- coding: utf-8 -*-
# Copyright 2015, 2016 OpenMarket Ltd
# Copyright 2018 New Vector Ltd
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
@ -496,13 +497,33 @@ class FederationServer(FederationBase):
def _handle_received_pdu(self, origin, pdu):
""" Process a PDU received in a federation /send/ transaction.
If the event is invalid, then this method throws a FederationError.
(The error will then be logged and sent back to the sender (which
probably won't do anything with it), and other events in the
transaction will be processed as normal).
It is likely that we'll then receive other events which refer to
this rejected_event in their prev_events, etc. When that happens,
we'll attempt to fetch the rejected event again, which will presumably
fail, so those second-generation events will also get rejected.
Eventually, we get to the point where there are more than 10 events
between any new events and the original rejected event. Since we
only try to backfill 10 events deep on received pdu, we then accept the
new event, possibly introducing a discontinuity in the DAG, with new
forward extremities, so normal service is approximately returned,
until we try to backfill across the discontinuity.
Args:
origin (str): server which sent the pdu
pdu (FrozenEvent): received pdu
Returns (Deferred): completes with None
Raises: FederationError if the signatures / hash do not match
"""
Raises: FederationError if the signatures / hash do not match, or
if the event was unacceptable for any other reason (eg, too large,
too many prev_events, couldn't find the prev_events)
"""
# check that it's actually being sent from a valid destination to
# workaround bug #1753 in 0.18.5 and 0.18.6
if origin != get_domain_from_id(pdu.event_id):

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@ -15,8 +15,14 @@
# limitations under the License.
"""Contains handlers for federation events."""
import httplib
import itertools
import logging
from signedjson.key import decode_verify_key_bytes
from signedjson.sign import verify_signed_json
from twisted.internet import defer
from unpaddedbase64 import decode_base64
from ._base import BaseHandler
@ -43,10 +49,6 @@ from synapse.util.retryutils import NotRetryingDestination
from synapse.util.distributor import user_joined_room
from twisted.internet import defer
import itertools
import logging
logger = logging.getLogger(__name__)
@ -115,6 +117,19 @@ class FederationHandler(BaseHandler):
logger.debug("Already seen pdu %s", pdu.event_id)
return
# do some initial sanity-checking of the event. In particular, make
# sure it doesn't have hundreds of prev_events or auth_events, which
# could cause a huge state resolution or cascade of event fetches.
try:
self._sanity_check_event(pdu)
except SynapseError as err:
raise FederationError(
"ERROR",
err.code,
err.msg,
affected=pdu.event_id,
)
# If we are currently in the process of joining this room, then we
# queue up events for later processing.
if pdu.room_id in self.room_queues:
@ -519,9 +534,16 @@ class FederationHandler(BaseHandler):
def backfill(self, dest, room_id, limit, extremities):
""" Trigger a backfill request to `dest` for the given `room_id`
This will attempt to get more events from the remote. This may return
be successfull and still return no events if the other side has no new
events to offer.
This will attempt to get more events from the remote. If the other side
has no new events to offer, this will return an empty list.
As the events are received, we check their signatures, and also do some
sanity-checking on them. If any of the backfilled events are invalid,
this method throws a SynapseError.
TODO: make this more useful to distinguish failures of the remote
server from invalid events (there is probably no point in trying to
re-fetch invalid events from every other HS in the room.)
"""
if dest == self.server_name:
raise SynapseError(400, "Can't backfill from self.")
@ -533,6 +555,16 @@ class FederationHandler(BaseHandler):
extremities=extremities,
)
# ideally we'd sanity check the events here for excess prev_events etc,
# but it's hard to reject events at this point without completely
# breaking backfill in the same way that it is currently broken by
# events whose signature we cannot verify (#3121).
#
# So for now we accept the events anyway. #3124 tracks this.
#
# for ev in events:
# self._sanity_check_event(ev)
# Don't bother processing events we already have.
seen_events = yield self.store.have_events_in_timeline(
set(e.event_id for e in events)
@ -835,6 +867,38 @@ class FederationHandler(BaseHandler):
defer.returnValue(False)
def _sanity_check_event(self, ev):
"""
Do some early sanity checks of a received event
In particular, checks it doesn't have an excessive number of
prev_events or auth_events, which could cause a huge state resolution
or cascade of event fetches.
Args:
ev (synapse.events.EventBase): event to be checked
Returns: None
Raises:
SynapseError if the event does not pass muster
"""
if len(ev.prev_events) > 20:
logger.warn("Rejecting event %s which has %i prev_events",
ev.event_id, len(ev.prev_events))
raise SynapseError(
httplib.BAD_REQUEST,
"Too many prev_events",
)
if len(ev.auth_events) > 10:
logger.warn("Rejecting event %s which has %i auth_events",
ev.event_id, len(ev.auth_events))
raise SynapseError(
httplib.BAD_REQUEST,
"Too many auth_events",
)
@defer.inlineCallbacks
def send_invite(self, target_host, event):
""" Sends the invite to the remote server for signing.