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
This commit is contained in:
Richard van der Hoff 2018-05-01 16:19:39 +01:00
parent 28dd536e80
commit 33f469ba19
3 changed files with 26 additions and 4 deletions

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@ -16,6 +16,9 @@
"""Contains constants from the specification.""" """Contains constants from the specification."""
# the "depth" field on events is limited to 2**63 - 1
MAX_DEPTH = 2**63 - 1
class Membership(object): class Membership(object):

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@ -14,7 +14,10 @@
# limitations under the License. # limitations under the License.
import logging 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.crypto.event_signing import check_event_content_hash
from synapse.events import FrozenEvent from synapse.events import FrozenEvent
from synapse.events.utils import prune_event from synapse.events.utils import prune_event
@ -190,11 +193,23 @@ def event_from_pdu_json(pdu_json, outlier=False):
FrozenEvent FrozenEvent
Raises: 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, # we could probably enforce a bunch of other fields here (room_id, sender,
# origin, etc etc) # 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( event = FrozenEvent(
pdu_json pdu_json
) )

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@ -16,7 +16,7 @@
from twisted.internet import defer, reactor from twisted.internet import defer, reactor
from twisted.python.failure import Failure 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.api.errors import AuthError, Codes, SynapseError
from synapse.crypto.event_signing import add_hashes_and_signatures from synapse.crypto.event_signing import add_hashes_and_signatures
from synapse.events.utils import serialize_event from synapse.events.utils import serialize_event
@ -624,6 +624,10 @@ class EventCreationHandler(object):
if prev_events_and_hashes: if prev_events_and_hashes:
depth = max([d for _, _, d in prev_events_and_hashes]) + 1 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: else:
depth = 1 depth = 1