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f0aec0abef
* Raise a dedicated `InvalidEventSignatureError` from `_check_sigs_on_pdu` * Downgrade logging about redactions to DEBUG this can be very spammy during a room join, and it's not very useful. * Raise `InvalidEventSignatureError` from `_check_sigs_and_hash` ... and, more importantly, move the logging out to the callers. * changelog
276 lines
10 KiB
Python
276 lines
10 KiB
Python
# 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 typing import TYPE_CHECKING
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from synapse.api.constants import MAX_DEPTH, EventContentFields, 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.types import JsonDict, get_domain_from_id
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if TYPE_CHECKING:
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from synapse.server import HomeServer
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logger = logging.getLogger(__name__)
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class InvalidEventSignatureError(RuntimeError):
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"""Raised when the signature on an event is invalid.
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The stringification of this exception is just the error message without reference
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to the event id. The event id is available as a property.
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"""
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def __init__(self, message: str, event_id: str):
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super().__init__(message)
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self.event_id = event_id
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class FederationBase:
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def __init__(self, hs: "HomeServer"):
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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_datastores().main
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self._clock = hs.get_clock()
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async def _check_sigs_and_hash(
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self, room_version: RoomVersion, pdu: EventBase
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) -> EventBase:
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"""Checks that event is correctly signed by the sending server.
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Also checks the content hash, and redacts the event if there is a mismatch.
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Also runs the event through the spam checker; if it fails, redacts the event
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and flags it as soft-failed.
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Args:
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room_version: The room version of the PDU
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pdu: the event to be checked
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Returns:
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* the original event if the checks pass
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* a redacted version of the event (if the signature
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matched but the hash did not). In this case a warning will be logged.
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Raises:
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InvalidEventSignatureError if the signature check failed. Nothing
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will be logged in this case.
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"""
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await _check_sigs_on_pdu(self.keyring, room_version, pdu)
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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.debug(
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"Event %s seems to have been redacted; using our redacted 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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spam_check = await self.spam_checker.check_event_for_spam(pdu)
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if spam_check != self.spam_checker.NOT_SPAM:
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logger.warning("Event contains spam, soft-failing %s", pdu.event_id)
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# we redact (to save disk space) as well as soft-failing (to stop
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# using the event in prev_events).
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redacted_event = prune_event(pdu)
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redacted_event.internal_metadata.soft_failed = True
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return redacted_event
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return pdu
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async def _check_sigs_on_pdu(
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keyring: Keyring, room_version: RoomVersion, pdu: EventBase
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) -> None:
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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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Raises:
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InvalidEventSignatureError if the event wasn't correctly signed.
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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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# 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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sender_domain = get_domain_from_id(pdu.sender)
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if not _is_invite_via_3pid(pdu):
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try:
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await keyring.verify_event_for_server(
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sender_domain,
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pdu,
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pdu.origin_server_ts if room_version.enforce_key_validity else 0,
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)
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except Exception as e:
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raise InvalidEventSignatureError(
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f"unable to verify signature for sender domain {sender_domain}: {e}",
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pdu.event_id,
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) from None
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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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event_domain = get_domain_from_id(pdu.event_id)
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if event_domain != sender_domain:
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try:
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await keyring.verify_event_for_server(
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event_domain,
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pdu,
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pdu.origin_server_ts if room_version.enforce_key_validity else 0,
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)
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except Exception as e:
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raise InvalidEventSignatureError(
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f"unable to verify signature for event domain {event_domain}: {e}",
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pdu.event_id,
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) from None
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# If this is a join event for a restricted room it may have been authorised
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# via a different server from the sending server. Check those signatures.
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if (
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room_version.msc3083_join_rules
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and pdu.type == EventTypes.Member
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and pdu.membership == Membership.JOIN
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and EventContentFields.AUTHORISING_USER in pdu.content
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):
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authorising_server = get_domain_from_id(
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pdu.content[EventContentFields.AUTHORISING_USER]
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)
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try:
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await keyring.verify_event_for_server(
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authorising_server,
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pdu,
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pdu.origin_server_ts if room_version.enforce_key_validity else 0,
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)
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except Exception as e:
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raise InvalidEventSignatureError(
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f"unable to verify signature for authorising serve {authorising_server}: {e}",
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pdu.event_id,
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) from 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(pdu_json: JsonDict, room_version: RoomVersion) -> 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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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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# Strip any unauthorized values from "unsigned" if they exist
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if "unsigned" in pdu_json:
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_strip_unsigned_values(pdu_json)
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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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return event
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def _strip_unsigned_values(pdu_dict: JsonDict) -> None:
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"""
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Strip any unsigned values unless specifically allowed, as defined by the whitelist.
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pdu: the json dict to strip values from. Note that the dict is mutated by this
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function
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"""
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unsigned = pdu_dict["unsigned"]
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if not isinstance(unsigned, dict):
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pdu_dict["unsigned"] = {}
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if pdu_dict["type"] == "m.room.member":
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whitelist = ["knock_room_state", "invite_room_state", "age"]
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else:
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whitelist = ["age"]
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filtered_unsigned = {k: v for k, v in unsigned.items() if k in whitelist}
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pdu_dict["unsigned"] = filtered_unsigned
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