• Mark Tyneway's avatar
    l2geth: fix for `gas-oracle` race condition · 5c0e90aa
    Mark Tyneway authored
    Prevent the error being returned in consensus for when
    the user does not have enough balance. The policy level
    check *must* filter out transactions that do not have
    enough gas to pay for their execution. The policy
    level check happens in the `SyncService`. This change
    gracefully handles the race condition where a user transaction
    passes the policy level check as a `gas-oracle` transaction
    is executing and updating the gas prices. If the gas price
    goes up and the user transaction no longer can afford execution,
    then it will return an error from consensus.
    5c0e90aa
state_transition.go 9.02 KB
// Copyright 2014 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package core

import (
	"errors"
	"math"
	"math/big"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/common/hexutil"
	"github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/core/vm"
	"github.com/ethereum/go-ethereum/log"
	"github.com/ethereum/go-ethereum/params"
	"github.com/ethereum/go-ethereum/rollup/fees"
	"github.com/ethereum/go-ethereum/rollup/rcfg"
)

var (
	errInsufficientBalanceForGas = errors.New("insufficient balance to pay for gas")
)

/*
The State Transitioning Model

A state transition is a change made when a transaction is applied to the current world state
The state transitioning model does all the necessary work to work out a valid new state root.

1) Nonce handling
2) Pre pay gas
3) Create a new state object if the recipient is \0*32
4) Value transfer
== If contract creation ==
  4a) Attempt to run transaction data
  4b) If valid, use result as code for the new state object
== end ==
5) Run Script section
6) Derive new state root
*/
type StateTransition struct {
	gp         *GasPool
	msg        Message
	gas        uint64
	gasPrice   *big.Int
	initialGas uint64
	value      *big.Int
	data       []byte
	state      vm.StateDB
	evm        *vm.EVM
	// UsingOVM
	l1Fee *big.Int
}

// Message represents a message sent to a contract.
type Message interface {
	From() common.Address
	//FromFrontier() (common.Address, error)
	To() *common.Address

	GasPrice() *big.Int
	Gas() uint64
	Value() *big.Int

	Nonce() uint64
	CheckNonce() bool
	Data() []byte

	L1Timestamp() uint64
	L1BlockNumber() *big.Int
	QueueOrigin() types.QueueOrigin
}

// IntrinsicGas computes the 'intrinsic gas' for a message with the given data.
func IntrinsicGas(data []byte, contractCreation, isHomestead bool, isEIP2028 bool) (uint64, error) {
	// Set the starting gas for the raw transaction
	var gas uint64
	if contractCreation && isHomestead {
		gas = params.TxGasContractCreation
	} else {
		gas = params.TxGas
	}
	// Bump the required gas by the amount of transactional data
	if len(data) > 0 {
		// Zero and non-zero bytes are priced differently
		var nz uint64
		for _, byt := range data {
			if byt != 0 {
				nz++
			}
		}
		// Make sure we don't exceed uint64 for all data combinations
		nonZeroGas := params.TxDataNonZeroGasFrontier
		if isEIP2028 {
			nonZeroGas = params.TxDataNonZeroGasEIP2028
		}
		if (math.MaxUint64-gas)/nonZeroGas < nz {
			return 0, vm.ErrOutOfGas
		}
		gas += nz * nonZeroGas

		z := uint64(len(data)) - nz
		if (math.MaxUint64-gas)/params.TxDataZeroGas < z {
			return 0, vm.ErrOutOfGas
		}
		gas += z * params.TxDataZeroGas
	}
	return gas, nil
}

// NewStateTransition initialises and returns a new state transition object.
func NewStateTransition(evm *vm.EVM, msg Message, gp *GasPool) *StateTransition {
	l1Fee := new(big.Int)
	if rcfg.UsingOVM {
		if msg.GasPrice().Cmp(common.Big0) != 0 {
			// Compute the L1 fee before the state transition
			// so it only has to be read from state one time.
			l1Fee, _ = fees.CalculateL1MsgFee(msg, evm.StateDB, nil)
		}
	}

	return &StateTransition{
		gp:       gp,
		evm:      evm,
		msg:      msg,
		gasPrice: msg.GasPrice(),
		value:    msg.Value(),
		data:     msg.Data(),
		state:    evm.StateDB,
		l1Fee:    l1Fee,
	}
}

// ApplyMessage computes the new state by applying the given message
// against the old state within the environment.
//
// ApplyMessage returns the bytes returned by any EVM execution (if it took place),
// the gas used (which includes gas refunds) and an error if it failed. An error always
// indicates a core error meaning that the message would always fail for that particular
// state and would never be accepted within a block.
func ApplyMessage(evm *vm.EVM, msg Message, gp *GasPool) ([]byte, uint64, bool, error) {
	return NewStateTransition(evm, msg, gp).TransitionDb()
}

// to returns the recipient of the message.
func (st *StateTransition) to() common.Address {
	if st.msg == nil || st.msg.To() == nil /* contract creation */ {
		return common.Address{}
	}
	return *st.msg.To()
}

func (st *StateTransition) useGas(amount uint64) error {
	if st.gas < amount {
		return vm.ErrOutOfGas
	}
	st.gas -= amount

	return nil
}

func (st *StateTransition) buyGas() error {
	mgval := new(big.Int).Mul(new(big.Int).SetUint64(st.msg.Gas()), st.gasPrice)
	if rcfg.UsingOVM {
		// Only charge the L1 fee for QueueOrigin sequencer transactions
		if st.msg.QueueOrigin() == types.QueueOriginSequencer {
			mgval = mgval.Add(mgval, st.l1Fee)
			if st.msg.CheckNonce() {
				log.Debug("Adding L1 fee", "l1-fee", st.l1Fee)
			}
		}
	}
	if st.state.GetBalance(st.msg.From()).Cmp(mgval) < 0 {
		if rcfg.UsingOVM {
			// Hack to prevent race conditions with the `gas-oracle`
			// where policy level balance checks pass and then fail
			// during consensus. The user gets some free gas
			// in this case.
			mgval = st.state.GetBalance(st.msg.From())
		} else {
			return errInsufficientBalanceForGas
		}
	}
	if err := st.gp.SubGas(st.msg.Gas()); err != nil {
		return err
	}
	st.gas += st.msg.Gas()

	st.initialGas = st.msg.Gas()
	st.state.SubBalance(st.msg.From(), mgval)
	return nil
}

func (st *StateTransition) preCheck() error {
	// Make sure this transaction's nonce is correct.
	if st.msg.CheckNonce() {
		nonce := st.state.GetNonce(st.msg.From())
		if nonce < st.msg.Nonce() {
			if rcfg.UsingOVM {
				// The nonce never increments for L1ToL2 txs
				if st.msg.QueueOrigin() == types.QueueOriginL1ToL2 {
					return st.buyGas()
				}
			}
			return ErrNonceTooHigh
		} else if nonce > st.msg.Nonce() {
			return ErrNonceTooLow
		}
	}
	return st.buyGas()
}

// TransitionDb will transition the state by applying the current message and
// returning the result including the used gas. It returns an error if failed.
// An error indicates a consensus issue.
func (st *StateTransition) TransitionDb() (ret []byte, usedGas uint64, failed bool, err error) {
	if err = st.preCheck(); err != nil {
		return
	}
	msg := st.msg
	sender := vm.AccountRef(msg.From())
	homestead := st.evm.ChainConfig().IsHomestead(st.evm.BlockNumber)
	istanbul := st.evm.ChainConfig().IsIstanbul(st.evm.BlockNumber)
	contractCreation := msg.To() == nil

	// Pay intrinsic gas
	gas, err := IntrinsicGas(st.data, contractCreation, homestead, istanbul)
	if err != nil {
		return nil, 0, false, err
	}
	if err = st.useGas(gas); err != nil {
		return nil, 0, false, err
	}

	var (
		evm = st.evm
		// vm errors do not effect consensus and are therefore
		// not assigned to err, except for insufficient balance
		// error.
		vmerr error
	)

	if contractCreation {
		ret, _, st.gas, vmerr = evm.Create(sender, st.data, st.gas, st.value)
	} else {
		// Increment the nonce for the next transaction
		st.state.SetNonce(msg.From(), st.state.GetNonce(msg.From())+1)
		ret, st.gas, vmerr = evm.Call(sender, st.to(), st.data, st.gas, st.value)
	}

	if vmerr != nil {
		log.Debug("VM returned with error", "err", vmerr, "ret", hexutil.Encode(ret))
		// The only possible consensus-error would be if there wasn't
		// sufficient balance to make the transfer happen. The first
		// balance transfer may never fail.
		if vmerr == vm.ErrInsufficientBalance {
			return nil, 0, false, vmerr
		}
	}
	st.refundGas()
	if rcfg.UsingOVM {
		// The L2 Fee is the same as the fee that is charged in the normal geth
		// codepath. Add the L1 fee to the L2 fee for the total fee that is sent
		// to the sequencer.
		l2Fee := new(big.Int).Mul(new(big.Int).SetUint64(st.gasUsed()), st.gasPrice)
		fee := new(big.Int).Add(st.l1Fee, l2Fee)
		st.state.AddBalance(evm.Coinbase, fee)
	} else {
		st.state.AddBalance(evm.Coinbase, new(big.Int).Mul(new(big.Int).SetUint64(st.gasUsed()), st.gasPrice))
	}

	return ret, st.gasUsed(), vmerr != nil, err
}

func (st *StateTransition) refundGas() {
	// Apply refund counter, capped to half of the used gas.
	refund := st.gasUsed() / 2
	if refund > st.state.GetRefund() {
		refund = st.state.GetRefund()
	}
	st.gas += refund

	// Return ETH for remaining gas, exchanged at the original rate.
	remaining := new(big.Int).Mul(new(big.Int).SetUint64(st.gas), st.gasPrice)
	st.state.AddBalance(st.msg.From(), remaining)

	// Also return remaining gas to the block gas counter so it is
	// available for the next transaction.
	st.gp.AddGas(st.gas)
}

// gasUsed returns the amount of gas used up by the state transition.
func (st *StateTransition) gasUsed() uint64 {
	return st.initialGas - st.gas
}