Verify tx gas isn't too large in VerifyTx (#3604)

Author: StephenButtolph

vms/platformvm/block/executor/manager.go

@@ -16,6 +16,7 @@ import (
 	"github.com/ava-labs/avalanchego/vms/platformvm/state"
 	"github.com/ava-labs/avalanchego/vms/platformvm/txs"
 	"github.com/ava-labs/avalanchego/vms/platformvm/txs/executor"
+	"github.com/ava-labs/avalanchego/vms/platformvm/txs/fee"
 	"github.com/ava-labs/avalanchego/vms/platformvm/txs/mempool"
 	"github.com/ava-labs/avalanchego/vms/platformvm/validators"
 )
@@ -168,6 +169,24 @@ func (m *manager) VerifyTx(tx *txs.Tx) error {
 		return fmt.Errorf("failed to advance the chain time: %w", err)
 	}
 
+	if timestamp := stateDiff.GetTimestamp(); m.txExecutorBackend.Config.UpgradeConfig.IsEtnaActivated(timestamp) {
+		complexity, err := fee.TxComplexity(tx.Unsigned)
+		if err != nil {
+			return fmt.Errorf("failed to calculate tx complexity: %w", err)
+		}
+		gas, err := complexity.ToGas(m.txExecutorBackend.Config.DynamicFeeConfig.Weights)
+		if err != nil {
+			return fmt.Errorf("failed to calculate tx gas: %w", err)
+		}
+
+		// TODO: After the mempool is updated, convert this check to use the
+		// maximum mempool capacity.
+		feeState := stateDiff.GetFeeState()
+		if gas > feeState.Capacity {
+			return fmt.Errorf("tx exceeds current gas capacity: %d > %d", gas, feeState.Capacity)
+		}
+	}
+
 	feeCalculator := state.PickFeeCalculator(m.txExecutorBackend.Config, stateDiff)
 	_, _, _, err = executor.StandardTx(
 		m.txExecutorBackend,