eth: early check the number of delivered blob transactions (#586)

Part of commit ethereum/go-ethereum@1f9b69b.

This commit add an early check for the number of delivered blob transactions
with header's blob gas used when receiving block body packet.

eth/downloader/queue.go

@@ -31,6 +31,7 @@ import (
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/metrics"
+	"github.com/ethereum/go-ethereum/params"
 	"github.com/ethereum/go-ethereum/trie"
 )
 
@@ -765,6 +766,21 @@ func (q *queue) DeliverBodies(id string, txLists [][]*types.Transaction, uncleLi
 		if types.CalcUncleHash(uncleLists[index]) != header.UncleHash {
 			return errInvalidBody
 		}
+		// Blocks must have a number of blobs corresponding to the header gas usage,
+		// and zero before the Cancun hardfork
+		var blobs int
+		for _, tx := range txLists[index] {
+			blobs += len(tx.BlobHashes())
+		}
+		if header.BlobGasUsed != nil {
+			if want := *header.BlobGasUsed / params.BlobTxBlobGasPerBlob; uint64(blobs) != want { // div because the header is surely good vs the body might be bloated
+				return errInvalidBody
+			}
+		} else {
+			if blobs != 0 {
+				return errInvalidBody
+			}
+		}
 		return nil
 	}