synapse-product/synapse/federation/federation_base.py

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# Copyright 2015, 2016 OpenMarket Ltd
# Copyright 2020 The Matrix.org Foundation C.I.C.
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#
# 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 typing import Iterable, List
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from twisted.internet import defer
from twisted.internet.defer import Deferred, DeferredList
from twisted.python.failure import Failure
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from synapse.api.constants import MAX_DEPTH, EventTypes, Membership
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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.logging.context import (
PreserveLoggingContext,
current_context,
make_deferred_yieldable,
)
from synapse.types import JsonDict, get_domain_from_id
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logger = logging.getLogger(__name__)
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class FederationBase:
def __init__(self, hs):
self.hs = hs
self.server_name = hs.hostname
self.keyring = hs.get_keyring()
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self.spam_checker = hs.get_spam_checker()
self.store = hs.get_datastore()
self._clock = hs.get_clock()
def _check_sigs_and_hash(
self, room_version: RoomVersion, pdu: EventBase
) -> Deferred:
return make_deferred_yieldable(
self._check_sigs_and_hashes(room_version, [pdu])[0]
)
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def _check_sigs_and_hashes(
self, room_version: RoomVersion, pdus: List[EventBase]
) -> List[Deferred]:
"""Checks that each of the received events is correctly signed by the
sending server.
Args:
room_version: The room version of the PDUs
pdus: the events to be checked
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Returns:
For each input event, a deferred which:
* returns the original event if the checks pass
* returns a redacted version of the event (if the signature
matched but the hash did not)
* throws a SynapseError if the signature check failed.
The deferreds run their callbacks in the sentinel
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"""
deferreds = _check_sigs_on_pdus(self.keyring, room_version, pdus)
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ctx = current_context()
@defer.inlineCallbacks
def callback(_, pdu: EventBase):
with PreserveLoggingContext(ctx):
if not check_event_content_hash(pdu):
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# 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()):
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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 = yield defer.ensureDeferred(
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
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def errback(failure: Failure, pdu: EventBase):
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failure.trap(SynapseError)
with PreserveLoggingContext(ctx):
logger.warning(
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"Signature check failed for %s: %s",
pdu.event_id,
failure.getErrorMessage(),
)
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return failure
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for deferred, pdu in zip(deferreds, pdus):
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deferred.addCallbacks(
callback, errback, callbackArgs=[pdu], errbackArgs=[pdu]
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)
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return deferreds
class PduToCheckSig(namedtuple("PduToCheckSig", ["pdu", "sender_domain", "deferreds"])):
pass
def _check_sigs_on_pdus(
keyring: Keyring, room_version: RoomVersion, pdus: Iterable[EventBase]
) -> List[Deferred]:
"""Check that the given events are correctly signed
Args:
keyring: keyring object to do the checks
room_version: the room version of the PDUs
pdus: the events to be checked
Returns:
A Deferred for each event in pdus, which will either succeed if
the signatures are valid, or fail (with a SynapseError) if not.
"""
# we want to check that the event is signed by:
#
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# (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.
#
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# (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.
pdus_to_check = [
PduToCheckSig(
pdu=p,
sender_domain=get_domain_from_id(p.sender),
deferreds=[],
)
for p in pdus
]
# 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)
pdus_to_check_sender = [p for p in pdus_to_check if not _is_invite_via_3pid(p.pdu)]
more_deferreds = keyring.verify_events_for_server(
[
(
p.sender_domain,
p.pdu,
p.pdu.origin_server_ts if room_version.enforce_key_validity else 0,
)
for p in pdus_to_check_sender
]
)
def sender_err(e, pdu_to_check):
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errmsg = "event id %s: unable to verify signature for sender %s: %s" % (
pdu_to_check.pdu.event_id,
pdu_to_check.sender_domain,
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e.getErrorMessage(),
)
raise SynapseError(403, errmsg, Codes.FORBIDDEN)
for p, d in zip(pdus_to_check_sender, more_deferreds):
d.addErrback(sender_err, p)
p.deferreds.append(d)
# 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:
pdus_to_check_event_id = [
p
for p in pdus_to_check
if p.sender_domain != get_domain_from_id(p.pdu.event_id)
]
more_deferreds = keyring.verify_events_for_server(
[
(
get_domain_from_id(p.pdu.event_id),
p.pdu,
p.pdu.origin_server_ts if room_version.enforce_key_validity else 0,
)
for p in pdus_to_check_event_id
]
)
def event_err(e, pdu_to_check):
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errmsg = (
"event id %s: unable to verify signature for event id domain: %s"
% (pdu_to_check.pdu.event_id, e.getErrorMessage())
)
raise SynapseError(403, errmsg, Codes.FORBIDDEN)
for p, d in zip(pdus_to_check_event_id, more_deferreds):
d.addErrback(event_err, p)
p.deferreds.append(d)
# replace lists of deferreds with single Deferreds
return [_flatten_deferred_list(p.deferreds) for p in pdus_to_check]
def _flatten_deferred_list(deferreds: List[Deferred]) -> Deferred:
"""Given a list of deferreds, either return the single deferred,
combine into a DeferredList, or return an already resolved deferred.
"""
if len(deferreds) > 1:
return DeferredList(deferreds, fireOnOneErrback=True, consumeErrors=True)
elif len(deferreds) == 1:
return deferreds[0]
else:
return defer.succeed(None)
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