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89a76d1889
If we receive an event that doesn't pass their content hash check (e.g. due to already being redacted) then we hit a bug which causes an exception to be raised, which then promplty stops the event (and request) from being processed. This effects all sorts of federation APIs, including joining rooms with a redacted state event.
335 lines
12 KiB
Python
335 lines
12 KiB
Python
# -*- coding: utf-8 -*-
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# Copyright 2015, 2016 OpenMarket Ltd
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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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import six
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from twisted.internet import defer
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from twisted.internet.defer import DeferredList
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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.crypto.event_signing import check_event_content_hash
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from synapse.events import FrozenEvent
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from synapse.events.utils import prune_event
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from synapse.http.servlet import assert_params_in_dict
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from synapse.types import get_domain_from_id
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from synapse.util import logcontext, unwrapFirstError
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logger = logging.getLogger(__name__)
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class FederationBase(object):
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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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@defer.inlineCallbacks
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def _check_sigs_and_hash_and_fetch(self, origin, pdus, outlier=False,
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include_none=False):
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"""Takes a list of PDUs and checks the signatures and hashs of each
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one. If a PDU fails its signature check then we check if we have it in
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the database and if not then request if from the originating server of
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that PDU.
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If a PDU fails its content hash check then it is redacted.
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The given list of PDUs are not modified, instead the function returns
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a new list.
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Args:
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pdu (list)
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outlier (bool)
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Returns:
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Deferred : A list of PDUs that have valid signatures and hashes.
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"""
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deferreds = self._check_sigs_and_hashes(pdus)
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@defer.inlineCallbacks
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def handle_check_result(pdu, deferred):
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try:
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res = yield logcontext.make_deferred_yieldable(deferred)
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except SynapseError:
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res = None
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if not res:
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# Check local db.
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res = yield self.store.get_event(
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pdu.event_id,
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allow_rejected=True,
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allow_none=True,
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)
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if not res and pdu.origin != origin:
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try:
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res = yield self.get_pdu(
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destinations=[pdu.origin],
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event_id=pdu.event_id,
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outlier=outlier,
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timeout=10000,
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)
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except SynapseError:
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pass
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if not res:
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logger.warn(
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"Failed to find copy of %s with valid signature",
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pdu.event_id,
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)
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defer.returnValue(res)
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handle = logcontext.preserve_fn(handle_check_result)
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deferreds2 = [
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handle(pdu, deferred)
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for pdu, deferred in zip(pdus, deferreds)
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]
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valid_pdus = yield logcontext.make_deferred_yieldable(
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defer.gatherResults(
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deferreds2,
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consumeErrors=True,
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)
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).addErrback(unwrapFirstError)
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if include_none:
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defer.returnValue(valid_pdus)
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else:
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defer.returnValue([p for p in valid_pdus if p])
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def _check_sigs_and_hash(self, pdu):
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return logcontext.make_deferred_yieldable(
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self._check_sigs_and_hashes([pdu])[0],
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)
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def _check_sigs_and_hashes(self, pdus):
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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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pdus (list[FrozenEvent]): the events to be checked
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Returns:
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list[Deferred]: 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 logcontext.
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"""
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deferreds = _check_sigs_on_pdus(self.keyring, pdus)
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ctx = logcontext.LoggingContext.current_context()
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def callback(_, pdu):
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with logcontext.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 (
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set(redacted_event.keys()) == set(pdu.keys()) and
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set(six.iterkeys(redacted_event.content))
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== set(six.iterkeys(pdu.content))
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):
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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, pdu.get_pdu_json(),
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)
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return redacted_event
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if self.spam_checker.check_event_for_spam(pdu):
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logger.warn(
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"Event contains spam, redacting %s: %s",
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pdu.event_id, 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, pdu):
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failure.trap(SynapseError)
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with logcontext.PreserveLoggingContext(ctx):
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logger.warn(
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"Signature check failed for %s: %s",
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pdu.event_id, 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,
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callbackArgs=[pdu],
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errbackArgs=[pdu],
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)
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return deferreds
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class PduToCheckSig(namedtuple("PduToCheckSig", [
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"pdu", "redacted_pdu_json", "event_id_domain", "sender_domain", "deferreds",
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])):
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pass
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def _check_sigs_on_pdus(keyring, pdus):
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"""Check that the given events are correctly signed
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Args:
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keyring (synapse.crypto.Keyring): keyring object to do the checks
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pdus (Collection[EventBase]): the events to be checked
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Returns:
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List[Deferred]: 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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# (currently this is written assuming the v1 room structure; we'll probably want a
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# separate function for checking v2 rooms)
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# we want to check that the event is signed by:
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#
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# (a) the server which created the event_id
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#
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# (b) 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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# 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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event_id_domain=get_domain_from_id(p.event_id),
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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 make sure that the event is signed by the event_id's domain
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deferreds = keyring.verify_json_objects_for_server([
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(p.event_id_domain, p.redacted_pdu_json)
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for p in pdus_to_check
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])
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for p, d in zip(pdus_to_check, deferreds):
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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.
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pdus_to_check_sender = [
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p for p in pdus_to_check
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if p.sender_domain != p.event_id_domain and not _is_invite_via_3pid(p.pdu)
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]
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more_deferreds = keyring.verify_json_objects_for_server([
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(p.sender_domain, p.redacted_pdu_json)
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for p in pdus_to_check_sender
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])
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for p, d in zip(pdus_to_check_sender, more_deferreds):
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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):
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"""Given a list of one or more deferreds, either return the single deferred, or
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combine into a DeferredList.
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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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else:
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assert len(deferreds) == 1
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return deferreds[0]
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def _is_invite_via_3pid(event):
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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(pdu_json, outlier=False):
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"""Construct a FrozenEvent from an event json received over federation
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Args:
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pdu_json (object): pdu as received over federation
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outlier (bool): True to mark this event as an outlier
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Returns:
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FrozenEvent
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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, ('event_id', 'type', 'depth'))
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depth = pdu_json['depth']
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if not isinstance(depth, six.integer_types):
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raise SynapseError(400, "Depth %r not an intger" % (depth, ),
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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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event = FrozenEvent(
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pdu_json
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)
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event.internal_metadata.outlier = outlier
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return event
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