Validate bid gas limit against the payload at bid.parent_block_hash

beacon_chain/consensus_object_pools/blockchain_dag.nim

@@ -1128,6 +1128,20 @@ proc loadExecutionAndParentBlockHash*(dag: ChainDAGRef, bid: BlockId):
     else:
       (Opt.some ZERO_HASH, Opt.some ZERO_HASH)
 
+proc loadExecutionGasLimit*(dag: ChainDAGRef, bid: BlockId): Opt[uint64] =
+  ## The `gas_limit` of the execution payload committed to by the block, i.e.
+  ## the bid's `gas_limit` post-Gloas (the envelope must match the bid).
+  let blockData = dag.getForkedBlock(bid).valueOr:
+    return Opt.none(uint64)
+
+  withBlck(blockData):
+    when consensusFork >= ConsensusFork.Gloas:
+      Opt.some forkyBlck.message.body.signed_execution_payload_bid.message.gas_limit
+    elif consensusFork in ConsensusFork.Bellatrix .. ConsensusFork.Fulu:
+      Opt.some forkyBlck.message.body.execution_payload.gas_limit
+    else:
+      Opt.none(uint64)
+
 proc loadExecutionAndParentBlockHash*(dag: ChainDAGRef, blck: BlockRef):
     tuple[blockHash: Opt[Eth2Digest], parentHash: Opt[Eth2Digest]] =
   if blck.executionBlockHash.isNone() or blck.executionParentHash.isNone():

beacon_chain/gossip_processing/gossip_validation.nim

@@ -2028,9 +2028,20 @@ proc validateExecutionPayloadBid*(
       # ... `is_gas_limit_target_compatible(parent_gas_limit, bid.gas_limit,
       # proposer_preferences.target_gas_limit)` is True, where
       # `parent_gas_limit` is the `gas_limit` of that execution payload.
+      #
+      # The execution payload identified by `bid.parent_block_hash` is either
+      # the parent block's own payload or one the parent block builds on
+      # (withheld), whose `gas_limit` can differ from the parent block's bid.
+      let parentPayloadBlck =
+        dag.executionParent(parentBlck, bid.parent_block_hash).valueOr:
+          return errIgnore(
+            "ExecutionPayloadBid: parent execution payload block unknown")
+      let parentGasLimit =
+        dag.loadExecutionGasLimit(parentPayloadBlck.bid).valueOr:
+          return errIgnore(
+            "ExecutionPayloadBid: parent execution payload gas limit unknown")
       if not is_gas_limit_target_compatible(
-          forkyState.data.latest_execution_payload_bid.gas_limit,
-          bid.gas_limit, seenPref.target_gas_limit):
+          parentGasLimit, bid.gas_limit, seenPref.target_gas_limit):
         return errIgnore("ExecutionPayloadBid: gas limit not target-compatible")
 
       # [IGNORE] bid.slot is the current slot or the next slot