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# Copyright 2015, 2016 OpenMarket Ltd
# Copyright 2020 The Matrix.org Foundation C.I.C.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# 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.
import logging
from collections import namedtuple
from synapse.api.constants import MAX_DEPTH, EventTypes, Membership
from synapse.api.errors import Codes, SynapseError
from synapse.api.room_versions import EventFormatVersions, RoomVersion
from synapse.crypto.event_signing import check_event_content_hash
from synapse.crypto.keyring import Keyring
from synapse.events import EventBase, make_event_from_dict
from synapse.events.utils import prune_event, validate_canonicaljson
from synapse.http.servlet import assert_params_in_dict
from synapse.types import JsonDict, get_domain_from_id
logger = logging.getLogger(__name__)
class FederationBase:
def __init__(self, hs):
self.hs = hs
self.server_name = hs.hostname
self.keyring = hs.get_keyring()
self.spam_checker = hs.get_spam_checker()
self.store = hs.get_datastore()
self._clock = hs.get_clock()
async def _check_sigs_and_hash(
self, room_version: RoomVersion, pdu: EventBase
) -> EventBase:
"""Checks that event is correctly signed by the sending server.
Args:
room_version: The room version of the PDU
pdu: the event to be checked
Returns:
* the original event if the checks pass
* a redacted version of the event (if the signature
matched but the hash did not)
* throws a SynapseError if the signature check failed."""
try:
await _check_sigs_on_pdu(self.keyring, room_version, pdu)
except SynapseError as e:
logger.warning(
"Signature check failed for %s: %s",
pdu.event_id,
e,
)
raise
if not check_event_content_hash(pdu):
# let's try to distinguish between failures because the event was
# redacted (which are somewhat expected) vs actual ball-tampering
# incidents.
#
# This is just a heuristic, so we just assume that if the keys are
# about the same between the redacted and received events, then the
# received event was probably a redacted copy (but we then use our
# *actual* redacted copy to be on the safe side.)
redacted_event = prune_event(pdu)
if set(redacted_event.keys()) == set(pdu.keys()) and set(
redacted_event.content.keys()
) == set(pdu.content.keys()):
logger.info(
"Event %s seems to have been redacted; using our redacted copy",
pdu.event_id,
)
else:
logger.warning(
"Event %s content has been tampered, redacting",
pdu.event_id,
)
return redacted_event
result = await self.spam_checker.check_event_for_spam(pdu)
if result:
logger.warning(
"Event contains spam, redacting %s: %s",
pdu.event_id,
pdu.get_pdu_json(),
)
return prune_event(pdu)
return pdu
class PduToCheckSig(namedtuple("PduToCheckSig", ["pdu", "sender_domain", "deferreds"])):
pass
async def _check_sigs_on_pdu(
keyring: Keyring, room_version: RoomVersion, pdu: EventBase
) -> None:
"""Check that the given events are correctly signed
Raise a SynapseError if the event wasn't correctly signed.
Args:
keyring: keyring object to do the checks
room_version: the room version of the PDUs
pdus: the events to be checked
"""
# we want to check that the event is signed by:
#
# (a) the sender's server
#
# - except in the case of invites created from a 3pid invite, which are exempt
# from this check, because the sender has to match that of the original 3pid
# invite, but the event may come from a different HS, for reasons that I don't
# entirely grok (why do the senders have to match? and if they do, why doesn't the
# joining server ask the inviting server to do the switcheroo with
# exchange_third_party_invite?).
#
# That's pretty awful, since redacting such an invite will render it invalid
# (because it will then look like a regular invite without a valid signature),
# and signatures are *supposed* to be valid whether or not an event has been
# redacted. But this isn't the worst of the ways that 3pid invites are broken.
#
# (b) for V1 and V2 rooms, the server which created the event_id
#
# let's start by getting the domain for each pdu, and flattening the event back
# to JSON.
# First we check that the sender event is signed by the sender's domain
# (except if its a 3pid invite, in which case it may be sent by any server)
if not _is_invite_via_3pid(pdu):
try:
await keyring.verify_event_for_server(
get_domain_from_id(pdu.sender),
pdu,
pdu.origin_server_ts if room_version.enforce_key_validity else 0,
)
except Exception as e:
errmsg = "event id %s: unable to verify signature for sender %s: %s" % (
pdu.event_id,
get_domain_from_id(pdu.sender),
e,
)
raise SynapseError(403, errmsg, Codes.FORBIDDEN)
# now let's look for events where the sender's domain is different to the
# event id's domain (normally only the case for joins/leaves), and add additional
# checks. Only do this if the room version has a concept of event ID domain
# (ie, the room version uses old-style non-hash event IDs).
if room_version.event_format == EventFormatVersions.V1 and get_domain_from_id(
pdu.event_id
) != get_domain_from_id(pdu.sender):
try:
await keyring.verify_event_for_server(
get_domain_from_id(pdu.event_id),
pdu,
pdu.origin_server_ts if room_version.enforce_key_validity else 0,
)
except Exception as e:
errmsg = (
"event id %s: unable to verify signature for event id domain %s: %s"
% (
pdu.event_id,
get_domain_from_id(pdu.event_id),
e,
)
)
raise SynapseError(403, errmsg, Codes.FORBIDDEN)
def _is_invite_via_3pid(event: EventBase) -> bool:
return (
event.type == EventTypes.Member
and event.membership == Membership.INVITE
and "third_party_invite" in event.content
)
def event_from_pdu_json(
pdu_json: JsonDict, room_version: RoomVersion, outlier: bool = False
) -> EventBase:
"""Construct an EventBase from an event json received over federation
Args:
pdu_json: pdu as received over federation
room_version: The version of the room this event belongs to
outlier: True to mark this event as an outlier
Raises:
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_dict(pdu_json, ("type", "depth"))
depth = pdu_json["depth"]
if not isinstance(depth, int):
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)
# Validate that the JSON conforms to the specification.
if room_version.strict_canonicaljson:
validate_canonicaljson(pdu_json)
event = make_event_from_dict(pdu_json, room_version)
event.internal_metadata.outlier = outlier
return event
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