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.
This commit is contained in:
Richard van der Hoff 2018-09-04 01:09:12 +01:00
parent 67dbe4c899
commit 5bf8bc79eb
1 changed files with 110 additions and 16 deletions

View File

@ -13,17 +13,20 @@
# 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
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__)
@ -133,34 +136,25 @@ class FederationBase(object):
* throws a SynapseError if the signature check failed.
The deferreds run their callbacks in the sentinel logcontext.
"""
redacted_pdus = [
prune_event(pdu)
for pdu in pdus
]
deferreds = self.keyring.verify_json_objects_for_server([
(p.origin, p.get_pdu_json())
for p in redacted_pdus
])
deferreds = _check_sigs_on_pdus(self.keyring, pdus)
ctx = logcontext.LoggingContext.current_context()
def callback(_, pdu, redacted):
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 redacted
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 redacted
return prune_event(pdu)
return pdu
@ -173,16 +167,116 @@ class FederationBase(object):
)
return failure
for deferred, pdu, redacted in zip(deferreds, pdus, redacted_pdus):
for deferred, pdu in zip(deferreds, pdus):
deferred.addCallbacks(
callback, errback,
callbackArgs=[pdu, redacted],
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