From f05401b78ece0f3751dd57da5f0f371b61222724 Mon Sep 17 00:00:00 2001
From: Andrew Ashikhmin <34320705+yperbasis@users.noreply.github.com>
Date: Wed, 6 Jul 2022 13:14:13 +0200
Subject: [PATCH] Don't write headBlockHash & co when FCU points to an old
 canonical block (#4650)

---
 eth/stagedsync/stage_headers.go | 25 +++++++++----------------
 1 file changed, 9 insertions(+), 16 deletions(-)

diff --git a/eth/stagedsync/stage_headers.go b/eth/stagedsync/stage_headers.go
index 4cd6e6e63..9b4bde039 100644
--- a/eth/stagedsync/stage_headers.go
+++ b/eth/stagedsync/stage_headers.go
@@ -332,22 +332,15 @@ func startHandlingForkChoice(
 	if headerHash == canonicalHash {
 		log.Info(fmt.Sprintf("[%s] Fork choice on previously known block", s.LogPrefix()))
 		cfg.hd.BeaconRequestList.Remove(requestId)
-		rawdb.WriteForkchoiceHead(tx, forkChoice.HeadBlockHash)
-		canonical, err := safeAndFinalizedBlocksAreCanonical(forkChoice, s, tx, cfg)
-		if err != nil {
-			log.Warn(fmt.Sprintf("[%s] Fork choice err", s.LogPrefix()), "err", err)
-			return nil, err
-		}
-		if canonical {
-			return &privateapi.PayloadStatus{
-				Status:          remote.EngineStatus_VALID,
-				LatestValidHash: headerHash,
-			}, nil
-		} else {
-			return &privateapi.PayloadStatus{
-				CriticalError: &privateapi.InvalidForkchoiceStateErr,
-			}, nil
-		}
+		// Per the Engine API spec:
+		// Client software MAY skip an update of the forkchoice state and MUST NOT begin a payload build process
+		// if forkchoiceState.headBlockHash references an ancestor of the head of canonical chain.
+		// In the case of such an event, client software MUST return
+		// {payloadStatus: {status: VALID, latestValidHash: forkchoiceState.headBlockHash, validationError: null}, payloadId: null}.
+		return &privateapi.PayloadStatus{
+			Status:          remote.EngineStatus_VALID,
+			LatestValidHash: headerHash,
+		}, nil
 	}
 
 	if cfg.memoryOverlay && headerHash == cfg.hd.GetNextForkHash() {