From 33f469ba19586bbafa0cf2c7d7c35463bdab87eb Mon Sep 17 00:00:00 2001 From: Richard van der Hoff Date: Tue, 1 May 2018 16:19:39 +0100 Subject: [PATCH] Apply some limits to depth to counter abuse * When creating a new event, cap its depth to 2^63 - 1 * When receiving events, reject any without a sensible depth As per https://docs.google.com/document/d/1I3fi2S-XnpO45qrpCsowZv8P8dHcNZ4fsBsbOW7KABI --- synapse/api/constants.py | 3 +++ synapse/federation/federation_base.py | 21 ++++++++++++++++++--- synapse/handlers/message.py | 6 +++++- 3 files changed, 26 insertions(+), 4 deletions(-) diff --git a/synapse/api/constants.py b/synapse/api/constants.py index 489efb7f8..5baba4396 100644 --- a/synapse/api/constants.py +++ b/synapse/api/constants.py @@ -16,6 +16,9 @@ """Contains constants from the specification.""" +# the "depth" field on events is limited to 2**63 - 1 +MAX_DEPTH = 2**63 - 1 + class Membership(object): diff --git a/synapse/federation/federation_base.py b/synapse/federation/federation_base.py index 79eaa3103..4cc98a3fe 100644 --- a/synapse/federation/federation_base.py +++ b/synapse/federation/federation_base.py @@ -14,7 +14,10 @@ # limitations under the License. import logging -from synapse.api.errors import SynapseError +import six + +from synapse.api.constants import MAX_DEPTH +from synapse.api.errors import SynapseError, Codes from synapse.crypto.event_signing import check_event_content_hash from synapse.events import FrozenEvent from synapse.events.utils import prune_event @@ -190,11 +193,23 @@ def event_from_pdu_json(pdu_json, outlier=False): FrozenEvent Raises: - SynapseError: if the pdu is missing required fields + SynapseError: if the pdu is missing required fields or is otherwise + not a valid matrix event """ # we could probably enforce a bunch of other fields here (room_id, sender, # origin, etc etc) - assert_params_in_request(pdu_json, ('event_id', 'type')) + assert_params_in_request(pdu_json, ('event_id', 'type', 'depth')) + + depth = pdu_json['depth'] + if not isinstance(depth, six.integer_types): + raise SynapseError(400, "Depth %r not an intger" % (depth, ), + Codes.BAD_JSON) + + if depth < 0: + raise SynapseError(400, "Depth too small", Codes.BAD_JSON) + elif depth > MAX_DEPTH: + raise SynapseError(400, "Depth too large", Codes.BAD_JSON) + event = FrozenEvent( pdu_json ) diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py index 21628a854..53beb2b9a 100644 --- a/synapse/handlers/message.py +++ b/synapse/handlers/message.py @@ -16,7 +16,7 @@ from twisted.internet import defer, reactor from twisted.python.failure import Failure -from synapse.api.constants import EventTypes, Membership +from synapse.api.constants import EventTypes, Membership, MAX_DEPTH from synapse.api.errors import AuthError, Codes, SynapseError from synapse.crypto.event_signing import add_hashes_and_signatures from synapse.events.utils import serialize_event @@ -624,6 +624,10 @@ class EventCreationHandler(object): if prev_events_and_hashes: depth = max([d for _, _, d in prev_events_and_hashes]) + 1 + # we cap depth of generated events, to ensure that they are not + # rejected by other servers (and so that they can be persisted in + # the db) + depth = min(depth, MAX_DEPTH) else: depth = 1