diff --git a/synapse/federation/federation_server.py b/synapse/federation/federation_server.py
index dbee404ea7..9a571e4fc7 100644
--- a/synapse/federation/federation_server.py
+++ b/synapse/federation/federation_server.py
@@ -618,7 +618,7 @@ class FederationServer(FederationBase):
)
yield self.handler.on_receive_pdu(
- origin, pdu, get_missing=True, sent_to_us_directly=True,
+ origin, pdu, sent_to_us_directly=True,
)
def __str__(self):
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 8d6bd7976d..2ccdc3bfa7 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -136,7 +136,7 @@ class FederationHandler(BaseHandler):
@defer.inlineCallbacks
def on_receive_pdu(
- self, origin, pdu, get_missing=True, sent_to_us_directly=False,
+ self, origin, pdu, sent_to_us_directly=False,
):
""" Process a PDU received via a federation /send/ transaction, or
via backfill of missing prev_events
@@ -145,7 +145,8 @@ class FederationHandler(BaseHandler):
origin (str): server which initiated the /send/ transaction. Will
be used to fetch missing events or state.
pdu (FrozenEvent): received PDU
- get_missing (bool): True if we should fetch missing prev_events
+ sent_to_us_directly (bool): True if this event was pushed to us; False if
+ we pulled it as the result of a missing prev_event.
Returns (Deferred): completes with None
"""
@@ -250,7 +251,7 @@ class FederationHandler(BaseHandler):
pdu.internal_metadata.outlier = True
elif min_depth and pdu.depth > min_depth:
missing_prevs = prevs - seen
- if get_missing and missing_prevs:
+ if sent_to_us_directly and missing_prevs:
# If we're missing stuff, ensure we only fetch stuff one
# at a time.
logger.info(
@@ -282,24 +283,46 @@ class FederationHandler(BaseHandler):
room_id, event_id, len(missing_prevs), shortstr(missing_prevs),
)
- if sent_to_us_directly and prevs - seen:
- # If they have sent it to us directly, and the server
- # isn't telling us about the auth events that it's
- # made a message referencing, we explode
- logger.warn(
- "[%s %s] Failed to fetch %d prev events: rejecting",
- room_id, event_id, len(prevs - seen),
- )
- raise FederationError(
- "ERROR",
- 403,
- (
- "Your server isn't divulging details about prev_events "
- "referenced in this event."
- ),
- affected=pdu.event_id,
- )
- elif prevs - seen:
+ if prevs - seen:
+ # We've still not been able to get all of the prev_events for this event.
+ #
+ # In this case, we need to fall back to asking another server in the
+ # federation for the state at this event. That's ok provided we then
+ # resolve the state against other bits of the DAG before using it (which
+ # will ensure that you can't just take over a room by sending an event,
+ # withholding its prev_events, and declaring yourself to be an admin in
+ # the subsequent state request).
+ #
+ # Now, if we're pulling this event as a missing prev_event, then clearly
+ # this event is not going to become the only forward-extremity and we are
+ # guaranteed to resolve its state against our existing forward
+ # extremities, so that should be fine.
+ #
+ # On the other hand, if this event was pushed to us, it is possible for
+ # it to become the only forward-extremity in the room, and we would then
+ # trust its state to be the state for the whole room. This is very bad.
+ # Further, if the event was pushed to us, there is no excuse for us not to
+ # have all the prev_events. We therefore reject any such events.
+ #
+ # XXX this really feels like it could/should be merged with the above,
+ # but there is an interaction with min_depth that I'm not really
+ # following.
+
+ if sent_to_us_directly:
+ logger.warn(
+ "[%s %s] Failed to fetch %d prev events: rejecting",
+ room_id, event_id, len(prevs - seen),
+ )
+ raise FederationError(
+ "ERROR",
+ 403,
+ (
+ "Your server isn't divulging details about prev_events "
+ "referenced in this event."
+ ),
+ affected=pdu.event_id,
+ )
+
# Calculate the state of the previous events, and
# de-conflict them to find the current state.
state_groups = []
@@ -464,7 +487,7 @@ class FederationHandler(BaseHandler):
yield self.on_receive_pdu(
origin,
ev,
- get_missing=False
+ sent_to_us_directly=False,
)
except FederationError as e:
if e.code == 403:
@@ -1112,7 +1135,7 @@ class FederationHandler(BaseHandler):
try:
logger.info("Processing queued PDU %s which was received "
"while we were joining %s", p.event_id, p.room_id)
- yield self.on_receive_pdu(origin, p)
+ yield self.on_receive_pdu(origin, p, sent_to_us_directly=True)
except Exception as e:
logger.warn(
"Error handling queued PDU %s from %s: %s",
|
