Remove destinations from sending if not whitelisted (#18484)

Co-authored-by: Andrew Morgan <andrew@amorgan.xyz>

changelog.d/18484.bugfix

@@ -0,0 +1 @@
+Remove destinations from sending if not whitelisted.

synapse/config/federation.py

@@ -94,5 +94,21 @@ class FederationConfig(Config):
             2**62,
         )
 
+    def is_domain_allowed_according_to_federation_whitelist(self, domain: str) -> bool:
+        """
+        Returns whether a domain is allowed according to the federation whitelist. If a
+        federation whitelist is not set, all domains are allowed.
+
+        Args:
+            domain: The domain to test.
+
+        Returns:
+            True if the domain is allowed or if a whitelist is not set, False otherwise.
+        """
+        if self.federation_domain_whitelist is None:
+            return True
+
+        return domain in self.federation_domain_whitelist
+
 
 _METRICS_FOR_DOMAINS_SCHEMA = {"type": "array", "items": {"type": "string"}}

synapse/federation/sender/__init__.py

@@ -342,6 +342,8 @@ class _DestinationWakeupQueue:
                 destination, _ = self.queue.popitem(last=False)
 
                 queue = self.sender._get_per_destination_queue(destination)
+                if queue is None:
+                    continue
 
                 if not queue._new_data_to_send:
                     # The per destination queue has already been woken up.
@@ -436,12 +438,23 @@ class FederationSender(AbstractFederationSender):
             self._wake_destinations_needing_catchup,
         )
 
-    def _get_per_destination_queue(self, destination: str) -> PerDestinationQueue:
+    def _get_per_destination_queue(
+        self, destination: str
+    ) -> Optional[PerDestinationQueue]:
         """Get or create a PerDestinationQueue for the given destination
 
         Args:
             destination: server_name of remote server
+
+        Returns:
+            None if the destination is not allowed by the federation whitelist.
+            Otherwise a PerDestinationQueue for this destination.
         """
+        if not self.hs.config.federation.is_domain_allowed_according_to_federation_whitelist(
+            destination
+        ):
+            return None
+
         queue = self._per_destination_queues.get(destination)
         if not queue:
             queue = PerDestinationQueue(self.hs, self._transaction_manager, destination)
@@ -718,6 +731,16 @@ class FederationSender(AbstractFederationSender):
         # track the fact that we have a PDU for these destinations,
         # to allow us to perform catch-up later on if the remote is unreachable
         # for a while.
+        # Filter out any destinations not present in the federation_domain_whitelist, if
+        # the whitelist exists. These destinations should not be sent to so let's not
+        # waste time or space keeping track of events destined for them.
+        destinations = [
+            d
+            for d in destinations
+            if self.hs.config.federation.is_domain_allowed_according_to_federation_whitelist(
+                d
+            )
+        ]
         await self.store.store_destination_rooms_entries(
             destinations,
             pdu.room_id,
@@ -732,7 +755,12 @@ class FederationSender(AbstractFederationSender):
         )
 
         for destination in destinations:
-            self._get_per_destination_queue(destination).send_pdu(pdu)
+            queue = self._get_per_destination_queue(destination)
+            # We expect `queue` to not be None as we already filtered out
+            # non-whitelisted destinations above.
+            assert queue is not None
+
+            queue.send_pdu(pdu)
 
     async def send_read_receipt(self, receipt: ReadReceipt) -> None:
         """Send a RR to any other servers in the room
@@ -841,12 +869,16 @@ class FederationSender(AbstractFederationSender):
         for domain in immediate_domains:
             # Add to destination queue and wake the destination up
             queue = self._get_per_destination_queue(domain)
+            if queue is None:
+                continue
             queue.queue_read_receipt(receipt)
             queue.attempt_new_transaction()
 
         for domain in delay_domains:
             # Add to destination queue...
             queue = self._get_per_destination_queue(domain)
+            if queue is None:
+                continue
             queue.queue_read_receipt(receipt)
 
             # ... and schedule the destination to be woken up.
@@ -882,9 +914,10 @@ class FederationSender(AbstractFederationSender):
             if self.is_mine_server_name(destination):
                 continue
 
-            self._get_per_destination_queue(destination).send_presence(
-                states, start_loop=False
-            )
+            queue = self._get_per_destination_queue(destination)
+            if queue is None:
+                continue
+            queue.send_presence(states, start_loop=False)
 
             self._destination_wakeup_queue.add_to_queue(destination)
 
@@ -934,6 +967,8 @@ class FederationSender(AbstractFederationSender):
             return
 
         queue = self._get_per_destination_queue(edu.destination)
+        if queue is None:
+            return
         if key:
             queue.send_keyed_edu(edu, key)
         else:
@@ -958,9 +993,15 @@ class FederationSender(AbstractFederationSender):
 
         for destination in destinations:
             if immediate:
-                self._get_per_destination_queue(destination).attempt_new_transaction()
+                queue = self._get_per_destination_queue(destination)
+                if queue is None:
+                    continue
+                queue.attempt_new_transaction()
             else:
-                self._get_per_destination_queue(destination).mark_new_data()
+                queue = self._get_per_destination_queue(destination)
+                if queue is None:
+                    continue
+                queue.mark_new_data()
                 self._destination_wakeup_queue.add_to_queue(destination)
 
     def wake_destination(self, destination: str) -> None:
@@ -979,7 +1020,9 @@ class FederationSender(AbstractFederationSender):
         ):
             return
 
-        self._get_per_destination_queue(destination).attempt_new_transaction()
+        queue = self._get_per_destination_queue(destination)
+        if queue is not None:
+            queue.attempt_new_transaction()
 
     @staticmethod
     def get_current_token() -> int:
@@ -1024,6 +1067,9 @@ class FederationSender(AbstractFederationSender):
                 d
                 for d in destinations_to_wake
                 if self._federation_shard_config.should_handle(self._instance_name, d)
+                and self.hs.config.federation.is_domain_allowed_according_to_federation_whitelist(
+                    d
+                )
             ]
 
             for destination in destinations_to_wake: