adjust verifyHeaders to validate GasLimit as calculated by new CalcGasLimitAndBaseFee function

consensus/ethash/consensus.go

@@ -265,8 +265,8 @@ func (ethash *Ethash) verifyHeader(chain consensus.ChainReader, header, parent *
 		return fmt.Errorf("invalid difficulty: have %v, want %v", header.Difficulty, expected)
 	}
 
-	// If we have not reached the EIP1559 activation block we need to verify that the GasLimit field is valid
-	if !chain.Config().IsEIP1559Finalized(header.Number) {
+	// If EIP1559 is not active we need to verify that the GasLimit field is valid according to the legacy rules
+	if !chain.Config().IsEIP1559(header.Number) {
 		// Verify that the gas limit is <= 2^63-1
 		cap := uint64(0x7fffffffffffffff)
 		if header.GasLimit > cap {
@@ -287,9 +287,9 @@ func (ethash *Ethash) verifyHeader(chain consensus.ChainReader, header, parent *
 		if uint64(diff) >= limit || header.GasLimit < params.MinGasLimit {
 			return fmt.Errorf("invalid gas limit: have %d, want %d += %d", header.GasLimit, parent.GasLimit, limit)
 		}
-	} else if header.GasLimit != 0 {
-		// If EIP1559 is finalized, GasLimit should be 0
-		return errGasLimitSet
+		// If EIP1559 is active, assert that the GasLimit field is valid according to the EIP1559 rules
+	} else if err := misc.VerifyEIP1559GasLimit(chain.Config(), header); err != nil {
+		return err
 	}
 
 	// Verify that the block number is parent's +1

consensus/misc/forks.go

@@ -27,11 +27,12 @@ import (
 )
 
 var (
-	errInvalidInitialBaseFee = fmt.Errorf("initial BaseFee must equal %d", params.EIP1559InitialBaseFee)
-	errInvalidBaseFee        = errors.New("invalid BaseFee")
-	errMissingParentBaseFee  = errors.New("parent header is missing BaseFee")
-	errMissingBaseFee        = errors.New("current header is missing BaseFee")
-	errHaveBaseFee           = fmt.Errorf("BaseFee should not be set before block %d", params.EIP1559ForkBlockNumber)
+	errInvalidInitialBaseFee           = fmt.Errorf("initial BaseFee must equal %d", params.EIP1559InitialBaseFee)
+	errInvalidBaseFee                  = errors.New("invalid BaseFee")
+	errMissingParentBaseFee            = errors.New("parent header is missing BaseFee")
+	errMissingBaseFee                  = errors.New("current header is missing BaseFee")
+	errHaveBaseFee                     = fmt.Errorf("BaseFee should not be set before block %d", params.EIP1559ForkBlockNumber)
+	errInvalidEIP1559FinalizedGasLimit = fmt.Errorf("after EIP1559 finalization, GasLimit must equal %d", params.MaxGasEIP1559)
 )
 
 // VerifyForkHashes verifies that blocks conforming to network hard-forks do have
@@ -89,3 +90,22 @@ func VerifyEIP1559BaseFee(config *params.ChainConfig, header, parent *types.Head
 	}
 	return nil
 }
+
+// VerifyEIP1559GasLimit verifies that the header.GasLimit field is valid for the current block height
+// Only call this after activation has been confirmed (config.IsEIP1559(header.Number) == true)
+func VerifyEIP1559GasLimit(config *params.ChainConfig, header *types.Header) error {
+	// If EIP1559 has been finalized then header.GasLimit should be equal to the MaxGasEIP1559 (entire limit is in EIP1559 pool)
+	if config.IsEIP1559Finalized(header.Number) {
+		if header.GasLimit != params.MaxGasEIP1559 {
+			return errInvalidEIP1559FinalizedGasLimit
+		}
+		return nil
+	}
+	// Else if we are between activation and finalization, header.GasLimit must be valid based on the decay function
+	numOfIncrements := new(big.Int).Sub(header.Number, config.EIP1559Block).Uint64()
+	expectedGasLimit := (params.MaxGasEIP1559 / 2) + (numOfIncrements * params.EIP1559GasIncrementAmount)
+	if header.GasLimit != expectedGasLimit {
+		return fmt.Errorf("invalid GasLimit: have %d, need %d", header.GasLimit, expectedGasLimit)
+	}
+	return nil
+}

core/block_validator.go

@@ -177,7 +177,7 @@ func calcGasLimitAndBaseFee(config *params.ChainConfig, parent *types.Block) (ui
 	div2 := new(big.Int).Div(div, new(big.Int).SetUint64(params.BaseFeeMaxChangeDenominator))
 	baseFee := new(big.Int).Add(parent.BaseFee(), div2)
 
-	// panic is the BaseFee is not valid
+	// Panic is the BaseFee is not valid
 	// A valid BASEFEE is one such that abs(BASEFEE - PARENT_BASEFEE) <= max(1, PARENT_BASEFEE // BASEFEE_MAX_CHANGE_DENOMINATOR)
 	diff := new(big.Int).Sub(baseFee, parent.BaseFee())
 	if diff.Sign() < 0 {
@@ -197,9 +197,8 @@ func calcGasLimitAndBaseFee(config *params.ChainConfig, parent *types.Block) (ui
 	}
 
 	// Otherwise calculate how much of the MaxGasEIP1559 serves as the limit for the EIP1559 pool
-	// We need to shift (MaxGasEIP1559 / 2) gas from the legacy pool into the eip1559 pool over the EIP1559DecayRange
-	gasIncrement := (params.MaxGasEIP1559 / 2) / params.EIP1559DecayRange // 10 gas shifted per block
+	// The GasLimit for the legacy pool is (params.MaxGasEIP1559 - eip1559GasLimit)
 	numOfIncrements := new(big.Int).Sub(height, config.EIP1559Block).Uint64()
-	eip1559GasLimit := (params.MaxGasEIP1559 / 2) + (numOfIncrements * gasIncrement)
+	eip1559GasLimit := (params.MaxGasEIP1559 / 2) + (numOfIncrements * params.EIP1559GasIncrementAmount)
 	return eip1559GasLimit, baseFee
 }