fix descent from split check

Author: eserilev

beacon_node/beacon_chain/src/attestation_verification.rs

@@ -1368,12 +1368,19 @@ fn verify_attestation_is_finalized_checkpoint_or_descendant<T: BeaconChainTypes>
     chain: &BeaconChain<T>,
 ) -> bool {
     // If we have a split block newer than finalization then we also ban attestations which are not
-    // descended from that split block.
+    // descended from that split block. It's important not to try checking `is_descendant` if
+    // finality is ahead of the split and the split block has been pruned, as `is_descendant` will
+    // return `false` in this case.
     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);
+    let finalized_slot = fork_choice
+        .finalized_checkpoint()
+        .epoch
+        .start_slot(T::EthSpec::slots_per_epoch());
+    let split = chain.store.get_split_info();
+    let is_descendant_from_split_block = split.slot == 0
+        || split.slot <= finalized_slot
+        || fork_choice.is_descendant(split.block_root, attestation_block_root);
 
     fork_choice.is_finalized_checkpoint_or_descendant(attestation_block_root)
         && is_descendant_from_split_block

beacon_node/network/src/network_beacon_processor/gossip_methods.rs

@@ -2893,27 +2893,6 @@ 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!(