316 lines
12 KiB
Python
316 lines
12 KiB
Python
# -*- coding: utf-8 -*-
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# Copyright 2015, 2016 OpenMarket Ltd
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# Copyright 2020 The Matrix.org Foundation C.I.C.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import logging
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from collections import namedtuple
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from typing import Iterable, List
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from twisted.internet import defer
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from twisted.internet.defer import Deferred, DeferredList
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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
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from synapse.api.room_versions import EventFormatVersions, RoomVersion
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from synapse.crypto.event_signing import check_event_content_hash
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from synapse.crypto.keyring import Keyring
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from synapse.events import EventBase, make_event_from_dict
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from synapse.events.utils import prune_event, validate_canonicaljson
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from synapse.http.servlet import assert_params_in_dict
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from synapse.logging.context import (
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PreserveLoggingContext,
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current_context,
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make_deferred_yieldable,
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)
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from synapse.types import JsonDict, get_domain_from_id
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logger = logging.getLogger(__name__)
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class FederationBase:
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def __init__(self, hs):
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self.hs = hs
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self.server_name = hs.hostname
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self.keyring = hs.get_keyring()
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self.spam_checker = hs.get_spam_checker()
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self.store = hs.get_datastore()
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self._clock = hs.get_clock()
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def _check_sigs_and_hash(
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self, room_version: RoomVersion, pdu: EventBase
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) -> Deferred:
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return make_deferred_yieldable(
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self._check_sigs_and_hashes(room_version, [pdu])[0]
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)
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def _check_sigs_and_hashes(
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self, room_version: RoomVersion, pdus: List[EventBase]
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) -> List[Deferred]:
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"""Checks that each of the received events is correctly signed by the
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sending server.
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Args:
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room_version: The room version of the PDUs
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pdus: the events to be checked
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Returns:
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For each input event, a deferred which:
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* returns the original event if the checks pass
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* returns a redacted version of the event (if the signature
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matched but the hash did not)
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* throws a SynapseError if the signature check failed.
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The deferreds run their callbacks in the sentinel
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"""
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deferreds = _check_sigs_on_pdus(self.keyring, room_version, pdus)
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ctx = current_context()
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@defer.inlineCallbacks
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def callback(_, pdu: EventBase):
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with PreserveLoggingContext(ctx):
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if not check_event_content_hash(pdu):
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# let's try to distinguish between failures because the event was
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# redacted (which are somewhat expected) vs actual ball-tampering
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# incidents.
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#
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# This is just a heuristic, so we just assume that if the keys are
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# about the same between the redacted and received events, then the
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# received event was probably a redacted copy (but we then use our
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# *actual* redacted copy to be on the safe side.)
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redacted_event = prune_event(pdu)
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if set(redacted_event.keys()) == set(pdu.keys()) and set(
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redacted_event.content.keys()
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) == set(pdu.content.keys()):
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logger.info(
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"Event %s seems to have been redacted; using our redacted "
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"copy",
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pdu.event_id,
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)
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else:
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logger.warning(
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"Event %s content has been tampered, redacting",
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pdu.event_id,
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)
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return redacted_event
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result = yield defer.ensureDeferred(
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self.spam_checker.check_event_for_spam(pdu)
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)
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if result:
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logger.warning(
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"Event contains spam, redacting %s: %s",
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pdu.event_id,
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pdu.get_pdu_json(),
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)
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return prune_event(pdu)
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return pdu
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def errback(failure: Failure, pdu: EventBase):
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failure.trap(SynapseError)
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with PreserveLoggingContext(ctx):
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logger.warning(
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"Signature check failed for %s: %s",
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pdu.event_id,
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failure.getErrorMessage(),
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)
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return failure
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for deferred, pdu in zip(deferreds, pdus):
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deferred.addCallbacks(
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callback, errback, callbackArgs=[pdu], errbackArgs=[pdu]
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)
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return deferreds
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class PduToCheckSig(
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namedtuple(
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"PduToCheckSig", ["pdu", "redacted_pdu_json", "sender_domain", "deferreds"]
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)
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):
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pass
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def _check_sigs_on_pdus(
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keyring: Keyring, room_version: RoomVersion, pdus: Iterable[EventBase]
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) -> List[Deferred]:
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"""Check that the given events are correctly signed
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Args:
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keyring: keyring object to do the checks
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room_version: the room version of the PDUs
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pdus: the events to be checked
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Returns:
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A Deferred for each event in pdus, which will either succeed if
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the signatures are valid, or fail (with a SynapseError) if not.
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"""
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# we want to check that the event is signed by:
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#
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# (a) the sender's server
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#
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# - except in the case of invites created from a 3pid invite, which are exempt
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# from this check, because the sender has to match that of the original 3pid
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# invite, but the event may come from a different HS, for reasons that I don't
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# entirely grok (why do the senders have to match? and if they do, why doesn't the
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# joining server ask the inviting server to do the switcheroo with
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# exchange_third_party_invite?).
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#
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# That's pretty awful, since redacting such an invite will render it invalid
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# (because it will then look like a regular invite without a valid signature),
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# and signatures are *supposed* to be valid whether or not an event has been
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# redacted. But this isn't the worst of the ways that 3pid invites are broken.
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#
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# (b) for V1 and V2 rooms, the server which created the event_id
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#
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# let's start by getting the domain for each pdu, and flattening the event back
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# to JSON.
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pdus_to_check = [
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PduToCheckSig(
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pdu=p,
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redacted_pdu_json=prune_event(p).get_pdu_json(),
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sender_domain=get_domain_from_id(p.sender),
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deferreds=[],
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)
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for p in pdus
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]
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# First we check that the sender event is signed by the sender's domain
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# (except if its a 3pid invite, in which case it may be sent by any server)
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pdus_to_check_sender = [p for p in pdus_to_check if not _is_invite_via_3pid(p.pdu)]
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more_deferreds = keyring.verify_json_objects_for_server(
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[
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(
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p.sender_domain,
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p.redacted_pdu_json,
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p.pdu.origin_server_ts if room_version.enforce_key_validity else 0,
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p.pdu.event_id,
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)
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for p in pdus_to_check_sender
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]
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)
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def sender_err(e, pdu_to_check):
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errmsg = "event id %s: unable to verify signature for sender %s: %s" % (
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pdu_to_check.pdu.event_id,
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pdu_to_check.sender_domain,
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e.getErrorMessage(),
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)
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raise SynapseError(403, errmsg, Codes.FORBIDDEN)
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for p, d in zip(pdus_to_check_sender, more_deferreds):
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d.addErrback(sender_err, p)
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p.deferreds.append(d)
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# now let's look for events where the sender's domain is different to the
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# event id's domain (normally only the case for joins/leaves), and add additional
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# checks. Only do this if the room version has a concept of event ID domain
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# (ie, the room version uses old-style non-hash event IDs).
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if room_version.event_format == EventFormatVersions.V1:
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pdus_to_check_event_id = [
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p
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for p in pdus_to_check
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if p.sender_domain != get_domain_from_id(p.pdu.event_id)
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]
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more_deferreds = keyring.verify_json_objects_for_server(
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[
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(
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get_domain_from_id(p.pdu.event_id),
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p.redacted_pdu_json,
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p.pdu.origin_server_ts if room_version.enforce_key_validity else 0,
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p.pdu.event_id,
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)
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for p in pdus_to_check_event_id
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]
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)
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def event_err(e, pdu_to_check):
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errmsg = (
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"event id %s: unable to verify signature for event id domain: %s"
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% (pdu_to_check.pdu.event_id, e.getErrorMessage())
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)
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raise SynapseError(403, errmsg, Codes.FORBIDDEN)
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for p, d in zip(pdus_to_check_event_id, more_deferreds):
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d.addErrback(event_err, p)
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p.deferreds.append(d)
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# replace lists of deferreds with single Deferreds
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return [_flatten_deferred_list(p.deferreds) for p in pdus_to_check]
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def _flatten_deferred_list(deferreds: List[Deferred]) -> Deferred:
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"""Given a list of deferreds, either return the single deferred,
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combine into a DeferredList, or return an already resolved deferred.
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"""
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if len(deferreds) > 1:
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return DeferredList(deferreds, fireOnOneErrback=True, consumeErrors=True)
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elif len(deferreds) == 1:
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return deferreds[0]
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else:
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return defer.succeed(None)
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def _is_invite_via_3pid(event: EventBase) -> bool:
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return (
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event.type == EventTypes.Member
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and event.membership == Membership.INVITE
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and "third_party_invite" in event.content
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)
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def event_from_pdu_json(
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pdu_json: JsonDict, room_version: RoomVersion, outlier: bool = False
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) -> EventBase:
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"""Construct an EventBase from an event json received over federation
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Args:
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pdu_json: pdu as received over federation
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room_version: The version of the room this event belongs to
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outlier: True to mark this event as an outlier
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Raises:
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SynapseError: if the pdu is missing required fields or is otherwise
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not a valid matrix event
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"""
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# we could probably enforce a bunch of other fields here (room_id, sender,
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# origin, etc etc)
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assert_params_in_dict(pdu_json, ("type", "depth"))
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depth = pdu_json["depth"]
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if not isinstance(depth, int):
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raise SynapseError(400, "Depth %r not an intger" % (depth,), Codes.BAD_JSON)
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if depth < 0:
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raise SynapseError(400, "Depth too small", Codes.BAD_JSON)
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elif depth > MAX_DEPTH:
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raise SynapseError(400, "Depth too large", Codes.BAD_JSON)
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# Validate that the JSON conforms to the specification.
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if room_version.strict_canonicaljson:
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validate_canonicaljson(pdu_json)
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event = make_event_from_dict(pdu_json, room_version)
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event.internal_metadata.outlier = outlier
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return event
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