return error if peer sent us a block we didn't expect with a height too far ahead/behind

blockchain/pool.go

@@ -40,6 +40,9 @@ const (
 	// Assuming a DSL connection (not a good choice) 128 Kbps (upload) ~ 15 KB/s,
 	// sending data across atlantic ~ 7.5 KB/s.
 	minRecvRate = 7680
+
+	// Maximum difference between current and new block's height.
+	maxDiffBetweenCurrentAndReceivedBlockHeight = 100
 )
 
 var peerTimeout = 15 * time.Second // not const so we can override with tests
@@ -230,8 +233,14 @@ func (pool *BlockPool) AddBlock(peerID p2p.ID, block *types.Block, blockSize int
 
 	requester := pool.requesters[block.Height]
 	if requester == nil {
-		// a block we didn't expect.
-		// TODO:if height is too far ahead, punish peer
+		pool.Logger.Info("peer sent us a block we didn't expect", "peer", peerID, "curHeight", pool.height, "blockHeight", block.Height)
+		diff := pool.height - block.Height
+		if diff < 0 {
+			diff *= -1
+		}
+		if diff > maxDiffBetweenCurrentAndReceivedBlockHeight {
+			pool.sendError(errors.New("peer sent us a block we didn't expect with a height too far ahead/behind"), peerID)
+		}
 		return
 	}