Add proper gas limit check through local computation (#14707)

* Add proper gas limit check through local computation

* Potuz's feedback

* Fix new line

CHANGELOG.md

@@ -33,6 +33,7 @@ The format is based on Keep a Changelog, and this project adheres to Semantic Ve
 - Added a Prometheus error counter metric for SSE requests.
 - Save light client updates and bootstraps in DB.
 - Added more comprehensive tests for `BlockToLightClientHeader`. [PR](https://github.com/prysmaticlabs/prysm/pull/14699)
+- Added proper gas limit check for header from the builder.
 - Added an error field to log `Finished building block`.
 - Implemented a new `EmptyExecutionPayloadHeader` function.
 

beacon-chain/rpc/prysm/v1alpha1/validator/proposer.go

@@ -237,7 +237,12 @@ func (vs *Server) BuildBlockParallel(ctx context.Context, sBlk interfaces.Signed
 		// There's no reason to try to get a builder bid if local override is true.
 		var builderBid builderapi.Bid
 		if !(local.OverrideBuilder || skipMevBoost) {
-			builderBid, err = vs.getBuilderPayloadAndBlobs(ctx, sBlk.Block().Slot(), sBlk.Block().ProposerIndex())
+			latestHeader, err := head.LatestExecutionPayloadHeader()
+			if err != nil {
+				return nil, status.Errorf(codes.Internal, "Could not get latest execution payload header: %v", err)
+			}
+			parentGasLimit := latestHeader.GasLimit()
+			builderBid, err = vs.getBuilderPayloadAndBlobs(ctx, sBlk.Block().Slot(), sBlk.Block().ProposerIndex(), parentGasLimit)
 			if err != nil {
 				builderGetPayloadMissCount.Inc()
 				log.WithError(err).Error("Could not get builder payload")

beacon-chain/rpc/prysm/v1alpha1/validator/proposer_bellatrix.go

@@ -51,6 +51,7 @@ var emptyTransactionsRoot = [32]byte{127, 254, 36, 30, 166, 1, 135, 253, 176, 24
 // blockBuilderTimeout is the maximum amount of time allowed for a block builder to respond to a
 // block request. This value is known as `BUILDER_PROPOSAL_DELAY_TOLERANCE` in builder spec.
 const blockBuilderTimeout = 1 * time.Second
+const gasLimitAdjustmentFactor = 1024
 
 // Sets the execution data for the block. Execution data can come from local EL client or remote builder depends on validator registration and circuit breaker conditions.
 func setExecutionData(ctx context.Context, blk interfaces.SignedBeaconBlock, local *blocks.GetPayloadResponse, bid builder.Bid, builderBoostFactor primitives.Gwei) (primitives.Wei, *enginev1.BlobsBundle, error) {
@@ -170,7 +171,11 @@ func setExecutionData(ctx context.Context, blk interfaces.SignedBeaconBlock, loc
 
 // This function retrieves the payload header and kzg commitments given the slot number and the validator index.
 // It's a no-op if the latest head block is not versioned bellatrix.
-func (vs *Server) getPayloadHeaderFromBuilder(ctx context.Context, slot primitives.Slot, idx primitives.ValidatorIndex) (builder.Bid, error) {
+func (vs *Server) getPayloadHeaderFromBuilder(
+	ctx context.Context,
+	slot primitives.Slot,
+	idx primitives.ValidatorIndex,
+	parentGasLimit uint64) (builder.Bid, error) {
 	ctx, span := trace.StartSpan(ctx, "ProposerServer.getPayloadHeaderFromBuilder")
 	defer span.End()
 
@@ -243,6 +248,16 @@ func (vs *Server) getPayloadHeaderFromBuilder(ctx context.Context, slot primitiv
 		return nil, fmt.Errorf("incorrect parent hash %#x != %#x", header.ParentHash(), h.BlockHash())
 	}
 
+	reg, err := vs.BlockBuilder.RegistrationByValidatorID(ctx, idx)
+	if err != nil {
+		log.WithError(err).Warn("Proposer: failed to get registration by validator ID, could not check gas limit")
+	} else {
+		gasLimit := expectedGasLimit(parentGasLimit, reg.GasLimit)
+		if gasLimit != header.GasLimit() {
+			return nil, fmt.Errorf("incorrect header gas limit %d != %d", gasLimit, header.GasLimit())
+		}
+	}
+
 	t, err := slots.ToTime(uint64(vs.TimeFetcher.GenesisTime().Unix()), slot)
 	if err != nil {
 		return nil, err
@@ -393,3 +408,32 @@ func setExecution(blk interfaces.SignedBeaconBlock, execution interfaces.Executi
 
 	return nil
 }
+
+// Calculates expected gas limit based on parent gas limit and target gas limit.
+// Spec code:
+//
+//	def expected_gas_limit(parent_gas_limit, target_gas_limit, adjustment_factor):
+//	 max_gas_limit_difference = (parent_gas_limit // adjustment_factor) - 1
+//	 if target_gas_limit > parent_gas_limit:
+//	     gas_diff = target_gas_limit - parent_gas_limit
+//	     return parent_gas_limit + min(gas_diff, max_gas_limit_difference)
+//	 else:
+//	     gas_diff = parent_gas_limit - target_gas_limit
+//	     return parent_gas_limit - min(gas_diff, max_gas_limit_difference)
+func expectedGasLimit(parentGasLimit, proposerGasLimit uint64) uint64 {
+	maxGasLimitDiff := uint64(0)
+	if parentGasLimit > gasLimitAdjustmentFactor {
+		maxGasLimitDiff = parentGasLimit/gasLimitAdjustmentFactor - 1
+	}
+	if proposerGasLimit > parentGasLimit {
+		if proposerGasLimit-parentGasLimit > maxGasLimitDiff {
+			return parentGasLimit + maxGasLimitDiff
+		}
+		return proposerGasLimit
+	}
+
+	if parentGasLimit-proposerGasLimit > maxGasLimitDiff {
+		return parentGasLimit - maxGasLimitDiff
+	}
+	return proposerGasLimit
+}