forked-synapse/synapse/federation/federation_base.py
Richard van der Hoff 804dd41e18 Check that signatures on events are valid
We should check that both the sender's server, and the server which created the
event_id (which may be different from whatever the remote server has told us
the origin is), have signed the event.
2018-09-05 13:08:07 +01:00

315 lines
10 KiB
Python

# -*- coding: utf-8 -*-
# Copyright 2015, 2016 OpenMarket Ltd
#
# 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
import six
from twisted.internet import defer
from twisted.internet.defer import DeferredList
from synapse.api.constants import MAX_DEPTH, EventTypes, Membership
from synapse.api.errors import Codes, SynapseError
from synapse.crypto.event_signing import check_event_content_hash
from synapse.events import FrozenEvent
from synapse.events.utils import prune_event
from synapse.http.servlet import assert_params_in_dict
from synapse.types import get_domain_from_id
from synapse.util import logcontext, unwrapFirstError
logger = logging.getLogger(__name__)
class FederationBase(object):
def __init__(self, hs):
self.hs = hs
self.server_name = hs.hostname
self.keyring = hs.get_keyring()
self.spam_checker = hs.get_spam_checker()
self.store = hs.get_datastore()
self._clock = hs.get_clock()
@defer.inlineCallbacks
def _check_sigs_and_hash_and_fetch(self, origin, pdus, outlier=False,
include_none=False):
"""Takes a list of PDUs and checks the signatures and hashs of each
one. If a PDU fails its signature check then we check if we have it in
the database and if not then request if from the originating server of
that PDU.
If a PDU fails its content hash check then it is redacted.
The given list of PDUs are not modified, instead the function returns
a new list.
Args:
pdu (list)
outlier (bool)
Returns:
Deferred : A list of PDUs that have valid signatures and hashes.
"""
deferreds = self._check_sigs_and_hashes(pdus)
@defer.inlineCallbacks
def handle_check_result(pdu, deferred):
try:
res = yield logcontext.make_deferred_yieldable(deferred)
except SynapseError:
res = None
if not res:
# Check local db.
res = yield self.store.get_event(
pdu.event_id,
allow_rejected=True,
allow_none=True,
)
if not res and pdu.origin != origin:
try:
res = yield self.get_pdu(
destinations=[pdu.origin],
event_id=pdu.event_id,
outlier=outlier,
timeout=10000,
)
except SynapseError:
pass
if not res:
logger.warn(
"Failed to find copy of %s with valid signature",
pdu.event_id,
)
defer.returnValue(res)
handle = logcontext.preserve_fn(handle_check_result)
deferreds2 = [
handle(pdu, deferred)
for pdu, deferred in zip(pdus, deferreds)
]
valid_pdus = yield logcontext.make_deferred_yieldable(
defer.gatherResults(
deferreds2,
consumeErrors=True,
)
).addErrback(unwrapFirstError)
if include_none:
defer.returnValue(valid_pdus)
else:
defer.returnValue([p for p in valid_pdus if p])
def _check_sigs_and_hash(self, pdu):
return logcontext.make_deferred_yieldable(
self._check_sigs_and_hashes([pdu])[0],
)
def _check_sigs_and_hashes(self, pdus):
"""Checks that each of the received events is correctly signed by the
sending server.
Args:
pdus (list[FrozenEvent]): the events to be checked
Returns:
list[Deferred]: 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 logcontext.
"""
deferreds = _check_sigs_on_pdus(self.keyring, pdus)
ctx = logcontext.LoggingContext.current_context()
def callback(_, pdu):
with logcontext.PreserveLoggingContext(ctx):
if not check_event_content_hash(pdu):
logger.warn(
"Event content has been tampered, redacting %s: %s",
pdu.event_id, pdu.get_pdu_json()
)
return prune_event(pdu)
if self.spam_checker.check_event_for_spam(pdu):
logger.warn(
"Event contains spam, redacting %s: %s",
pdu.event_id, pdu.get_pdu_json()
)
return prune_event(pdu)
return pdu
def errback(failure, pdu):
failure.trap(SynapseError)
with logcontext.PreserveLoggingContext(ctx):
logger.warn(
"Signature check failed for %s",
pdu.event_id,
)
return failure
for deferred, pdu in zip(deferreds, pdus):
deferred.addCallbacks(
callback, errback,
callbackArgs=[pdu],
errbackArgs=[pdu],
)
return deferreds
class PduToCheckSig(namedtuple("PduToCheckSig", [
"pdu", "redacted_pdu_json", "event_id_domain", "sender_domain", "deferreds",
])):
pass
def _check_sigs_on_pdus(keyring, pdus):
"""Check that the given events are correctly signed
Args:
keyring (synapse.crypto.Keyring): keyring object to do the checks
pdus (Collection[EventBase]): the events to be checked
Returns:
List[Deferred]: a Deferred for each event in pdus, which will either succeed if
the signatures are valid, or fail (with a SynapseError) if not.
"""
# (currently this is written assuming the v1 room structure; we'll probably want a
# separate function for checking v2 rooms)
# we want to check that the event is signed by:
#
# (a) the server which created the event_id
#
# (b) 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.
#
# let's start by getting the domain for each pdu, and flattening the event back
# to JSON.
pdus_to_check = [
PduToCheckSig(
pdu=p,
redacted_pdu_json=prune_event(p).get_pdu_json(),
event_id_domain=get_domain_from_id(p.event_id),
sender_domain=get_domain_from_id(p.sender),
deferreds=[],
)
for p in pdus
]
# first make sure that the event is signed by the event_id's domain
deferreds = keyring.verify_json_objects_for_server([
(p.event_id_domain, p.redacted_pdu_json)
for p in pdus_to_check
])
for p, d in zip(pdus_to_check, deferreds):
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.
pdus_to_check_sender = [
p for p in pdus_to_check
if p.sender_domain != p.event_id_domain and not _is_invite_via_3pid(p.pdu)
]
more_deferreds = keyring.verify_json_objects_for_server([
(p.sender_domain, p.redacted_pdu_json)
for p in pdus_to_check_sender
])
for p, d in zip(pdus_to_check_sender, more_deferreds):
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):
"""Given a list of one or more deferreds, either return the single deferred, or
combine into a DeferredList.
"""
if len(deferreds) > 1:
return DeferredList(deferreds, fireOnOneErrback=True, consumeErrors=True)
else:
assert len(deferreds) == 1
return deferreds[0]
def _is_invite_via_3pid(event):
return (
event.type == EventTypes.Member
and event.membership == Membership.INVITE
and "third_party_invite" in event.content
)
def event_from_pdu_json(pdu_json, outlier=False):
"""Construct a FrozenEvent from an event json received over federation
Args:
pdu_json (object): pdu as received over federation
outlier (bool): True to mark this event as an outlier
Returns:
FrozenEvent
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, ('event_id', 'type', 'depth'))
depth = pdu_json['depth']
if not isinstance(depth, six.integer_types):
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)
event = FrozenEvent(
pdu_json
)
event.internal_metadata.outlier = outlier
return event