diff options
| -rw-r--r-- | changelog.d/4814.feature | 1 | ||||
| -rw-r--r-- | synapse/events/__init__.py | 14 | ||||
| -rw-r--r-- | synapse/handlers/federation.py | 94 | ||||
| -rw-r--r-- | synapse/storage/events.py | 1 | ||||
| -rw-r--r-- | synapse/visibility.py | 4 |
5 files changed, 113 insertions, 1 deletions
diff --git a/changelog.d/4814.feature b/changelog.d/4814.feature new file mode 100644 index 0000000000..9433acd959 --- /dev/null +++ b/changelog.d/4814.feature @@ -0,0 +1 @@ +Add checks to incoming events over federation for events evading auth (aka "soft fail"). diff --git a/synapse/events/__init__.py b/synapse/events/__init__.py index 20c1ab4203..bd130f8816 100644 --- a/synapse/events/__init__.py +++ b/synapse/events/__init__.py @@ -77,6 +77,20 @@ class _EventInternalMetadata(object): """ return getattr(self, "recheck_redaction", False) + def is_soft_failed(self): + """Whether the event has been soft failed. + + Soft failed events should be handled as usual, except: + 1. They should not go down sync or event streams, or generally + sent to clients. + 2. They should not be added to the forward extremities (and + therefore not to current state). + + Returns: + bool + """ + return getattr(self, "soft_failed", False) + def _event_dict_property(key): # We want to be able to use hasattr with the event dict properties. diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py index 72b63d64d0..9eaf2d3e18 100644 --- a/synapse/handlers/federation.py +++ b/synapse/handlers/federation.py @@ -45,6 +45,7 @@ from synapse.api.errors import ( SynapseError, ) from synapse.crypto.event_signing import compute_event_signature +from synapse.event_auth import auth_types_for_event from synapse.events.validator import EventValidator from synapse.replication.http.federation import ( ReplicationCleanRoomRestServlet, @@ -1628,6 +1629,7 @@ class FederationHandler(BaseHandler): origin, event, state=state, auth_events=auth_events, + backfilled=backfilled, ) # reraise does not allow inlineCallbacks to preserve the stacktrace, so we @@ -1672,6 +1674,7 @@ class FederationHandler(BaseHandler): event, state=ev_info.get("state"), auth_events=ev_info.get("auth_events"), + backfilled=backfilled, ) defer.returnValue(res) @@ -1794,7 +1797,7 @@ class FederationHandler(BaseHandler): ) @defer.inlineCallbacks - def _prep_event(self, origin, event, state=None, auth_events=None): + def _prep_event(self, origin, event, state, auth_events, backfilled): """ Args: @@ -1802,6 +1805,7 @@ class FederationHandler(BaseHandler): event: state: auth_events: + backfilled (bool) Returns: Deferred, which resolves to synapse.events.snapshot.EventContext @@ -1843,12 +1847,100 @@ class FederationHandler(BaseHandler): context.rejected = RejectedReason.AUTH_ERROR + if not context.rejected: + yield self._check_for_soft_fail(event, state, backfilled) + if event.type == EventTypes.GuestAccess and not context.rejected: yield self.maybe_kick_guest_users(event) defer.returnValue(context) @defer.inlineCallbacks + def _check_for_soft_fail(self, event, state, backfilled): + """Checks if we should soft fail the event, if so marks the event as + such. + + Args: + event (FrozenEvent) + state (dict|None): The state at the event if we don't have all the + event's prev events + backfilled (bool): Whether the event is from backfill + + Returns: + Deferred + """ + # For new (non-backfilled and non-outlier) events we check if the event + # passes auth based on the current state. If it doesn't then we + # "soft-fail" the event. + do_soft_fail_check = not backfilled and not event.internal_metadata.is_outlier() + if do_soft_fail_check: + extrem_ids = yield self.store.get_latest_event_ids_in_room( + event.room_id, + ) + + extrem_ids = set(extrem_ids) + prev_event_ids = set(event.prev_event_ids()) + + if extrem_ids == prev_event_ids: + # If they're the same then the current state is the same as the + # state at the event, so no point rechecking auth for soft fail. + do_soft_fail_check = False + + if do_soft_fail_check: + room_version = yield self.store.get_room_version(event.room_id) + + # Calculate the "current state". + if state is not None: + # If we're explicitly given the state then we won't have all the + # prev events, and so we have a gap in the graph. In this case + # we want to be a little careful as we might have been down for + # a while and have an incorrect view of the current state, + # however we still want to do checks as gaps are easy to + # maliciously manufacture. + # + # So we use a "current state" that is actually a state + # resolution across the current forward extremities and the + # given state at the event. This should correctly handle cases + # like bans, especially with state res v2. + + state_sets = yield self.store.get_state_groups( + event.room_id, extrem_ids, + ) + state_sets = list(state_sets.values()) + state_sets.append(state) + current_state_ids = yield self.state_handler.resolve_events( + room_version, state_sets, event, + ) + current_state_ids = { + k: e.event_id for k, e in iteritems(current_state_ids) + } + else: + current_state_ids = yield self.state_handler.get_current_state_ids( + event.room_id, latest_event_ids=extrem_ids, + ) + + # Now check if event pass auth against said current state + auth_types = auth_types_for_event(event) + current_state_ids = [ + e for k, e in iteritems(current_state_ids) + if k in auth_types + ] + + current_auth_events = yield self.store.get_events(current_state_ids) + current_auth_events = { + (e.type, e.state_key): e for e in current_auth_events.values() + } + + try: + self.auth.check(room_version, event, auth_events=current_auth_events) + except AuthError as e: + logger.warn( + "Failed current state auth resolution for %r because %s", + event, e, + ) + event.internal_metadata.soft_failed = True + + @defer.inlineCallbacks def on_query_auth(self, origin, event_id, room_id, remote_auth_chain, rejects, missing): in_room = yield self.auth.check_host_in_room( diff --git a/synapse/storage/events.py b/synapse/storage/events.py index 06db9e56e6..990a5eaaae 100644 --- a/synapse/storage/events.py +++ b/synapse/storage/events.py @@ -537,6 +537,7 @@ class EventsStore(StateGroupWorkerStore, EventFederationStore, EventsWorkerStore new_events = [ event for event, ctx in event_contexts if not event.internal_metadata.is_outlier() and not ctx.rejected + and not event.internal_metadata.is_soft_failed() ] # start with the existing forward extremities diff --git a/synapse/visibility.py b/synapse/visibility.py index efec21673b..16c40cd74c 100644 --- a/synapse/visibility.py +++ b/synapse/visibility.py @@ -67,6 +67,10 @@ def filter_events_for_client(store, user_id, events, is_peeking=False, Returns: Deferred[list[synapse.events.EventBase]] """ + # Filter out events that have been soft failed so that we don't relay them + # to clients. + events = list(e for e in events if not e.internal_metadata.is_soft_failed()) + types = ( (EventTypes.RoomHistoryVisibility, ""), (EventTypes.Member, user_id), |