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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 typing import TYPE_CHECKING
-
- from synapse.api.constants import MAX_DEPTH, EventContentFields, 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
-
- if TYPE_CHECKING:
- from synapse.server import HomeServer
-
-
- logger = logging.getLogger(__name__)
-
-
- class FederationBase:
- def __init__(self, hs: "HomeServer"):
- self.hs = hs
-
- self.server_name = hs.hostname
- self.keyring = hs.get_keyring()
- self.spam_checker = hs.get_spam_checker()
- self.store = hs.get_datastores().main
- 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.
-
- Also checks the content hash, and redacts the event if there is a mismatch.
-
- Also runs the event through the spam checker; if it fails, redacts the event
- and flags it as soft-failed.
-
- 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)
-
- Raises:
- 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
-
- spam_check = await self.spam_checker.check_event_for_spam(pdu)
-
- if spam_check != self.spam_checker.NOT_SPAM:
- logger.warning("Event contains spam, soft-failing %s", pdu.event_id)
- # we redact (to save disk space) as well as soft-failing (to stop
- # using the event in prev_events).
- redacted_event = prune_event(pdu)
- redacted_event.internal_metadata.soft_failed = True
- return redacted_event
-
- return pdu
-
-
- 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)
-
- # If this is a join event for a restricted room it may have been authorised
- # via a different server from the sending server. Check those signatures.
- if (
- room_version.msc3083_join_rules
- and pdu.type == EventTypes.Member
- and pdu.membership == Membership.JOIN
- and EventContentFields.AUTHORISING_USER in pdu.content
- ):
- authorising_server = get_domain_from_id(
- pdu.content[EventContentFields.AUTHORISING_USER]
- )
- try:
- await keyring.verify_event_for_server(
- authorising_server,
- 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 authorising server %s: %s"
- % (
- pdu.event_id,
- authorising_server,
- 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) -> 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
-
- 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"))
-
- # Strip any unauthorized values from "unsigned" if they exist
- if "unsigned" in pdu_json:
- _strip_unsigned_values(pdu_json)
-
- 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)
- return event
-
-
- def _strip_unsigned_values(pdu_dict: JsonDict) -> None:
- """
- Strip any unsigned values unless specifically allowed, as defined by the whitelist.
-
- pdu: the json dict to strip values from. Note that the dict is mutated by this
- function
- """
- unsigned = pdu_dict["unsigned"]
-
- if not isinstance(unsigned, dict):
- pdu_dict["unsigned"] = {}
-
- if pdu_dict["type"] == "m.room.member":
- whitelist = ["knock_room_state", "invite_room_state", "age"]
- else:
- whitelist = ["age"]
-
- filtered_unsigned = {k: v for k, v in unsigned.items() if k in whitelist}
- pdu_dict["unsigned"] = filtered_unsigned
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