Reject attestations to blocks prior to the split

beacon_node/beacon_chain/src/attestation_verification.rs

@@ -858,6 +858,9 @@ impl<'a, T: BeaconChainTypes> IndexedUnaggregatedAttestation<'a, T> {
         // Check the attestation target root is consistent with the head root.
         verify_attestation_target_root::<T::EthSpec>(&head_block, attestation)?;
 
+        // Do not process an attestation that doesn't descend from the finalized root.
+        verify_attestation_is_finalized_checkpoint_or_descendant(attestation, chain)?;
+
         Ok(())
     }
 
@@ -1361,6 +1364,29 @@ pub fn verify_committee_index<E: EthSpec>(attestation: AttestationRef<E>) -> Res
     Ok(())
 }
 
+fn verify_attestation_is_finalized_checkpoint_or_descendant<T: BeaconChainTypes>(
+    attestation: AttestationRef<T::EthSpec>,
+    chain: &BeaconChain<T>,
+) -> Result<(), Error> {
+    // If we have a split block newer than finalization then we also ban attestations which are not
+    // descended from that split block.
+    let fork_choice = chain.canonical_head.fork_choice_read_lock();
+    let split = chain.store.get_split_info();
+    let attestation_block_root = attestation.data().beacon_block_root;
+    let is_descendant_from_split_block =
+        split.slot == 0 || fork_choice.is_descendant(split.block_root, attestation_block_root);
+
+    if fork_choice.is_finalized_checkpoint_or_descendant(attestation_block_root)
+        && is_descendant_from_split_block
+    {
+        Ok(())
+    } else {
+        Err(Error::HeadBlockFinalized {
+            attestation_block_root,
+        })
+    }
+}
+
 /// Assists in readability.
 type CommitteesPerSlot = u64;
 

beacon_node/network/src/network_beacon_processor/gossip_methods.rs

@@ -2893,6 +2893,27 @@ impl<T: BeaconChainTypes> NetworkBeaconProcessor<T> {
                 );
                 self.propagate_validation_result(message_id, peer_id, MessageAcceptance::Ignore);
             }
+            AttnError::NotFinalizedDescendant {
+                attestation_block_root,
+                attestation_slot,
+            } => {
+                error!(
+                    self.log,
+                    "Could not verify the attestation for gossip. Rejecting the attestation";
+                    "attestation_block_root" => ?attestation_block_root,
+                    "slot" => ?attestation_slot,
+                    "type" => ?attestation_type,
+                    "peer_id" => %peer_id,
+                );
+                // There's no reason for an honest and non-buggy client to be gossiping
+                // attestations that blatantly conflict with finalization.
+                self.gossip_penalize_peer(
+                    peer_id,
+                    PeerAction::LowToleranceError,
+                    "gossip_attestation_invalid",
+                );
+                self.propagate_validation_result(message_id, peer_id, MessageAcceptance::Reject);
+            }
         }
 
         debug!(