core: remove stray account creations in state transition (#16470)

The 'from' and 'to' methods on StateTransitions are reader methods and
shouldn't have inadvertent side effects on state.

It is safe to remove the check in 'from' because account existence is
implicitly checked by the nonce and balance checks. If the account has
non-zero balance or nonce, it must exist. Even if the sender account has
nonce zero at the start of the state transition or no balance, the nonce
is incremented before execution and the account will be created at that
time.

It is safe to remove the check in 'to' because the EVM creates the
account if necessary.

Fixes #15119

1 files changed, 16 insertions, 42 deletions

diff --git a/core/state_transition.go b/core/state_transition.go
index b19bc12e4..5654cd01e 100644
--- a/core/state_transition.go
+++ b/core/state_transition.go
@@ -132,28 +132,12 @@ func ApplyMessage(evm *vm.EVM, msg Message, gp *GasPool) ([]byte, uint64, bool,
 	return NewStateTransition(evm, msg, gp).TransitionDb()
 }
 
-func (st *StateTransition) from() vm.AccountRef {
-	f := st.msg.From()
-	if !st.state.Exist(f) {
-		st.state.CreateAccount(f)
+// 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 vm.AccountRef(f)
-}
-
-func (st *StateTransition) to() vm.AccountRef {
-	if st.msg == nil {
-		return vm.AccountRef{}
-	}
-	to := st.msg.To()
-	if to == nil {
-		return vm.AccountRef{} // contract creation
-	}
-
-	reference := vm.AccountRef(*to)
-	if !st.state.Exist(*to) {
-		st.state.CreateAccount(*to)
-	}
-	return reference
+	return *st.msg.To()
 }
 
 func (st *StateTransition) useGas(amount uint64) error {
@@ -166,12 +150,8 @@ func (st *StateTransition) useGas(amount uint64) error {
 }
 
 func (st *StateTransition) buyGas() error {
-	var (
-		state  = st.state
-		sender = st.from()
-	)
 	mgval := new(big.Int).Mul(new(big.Int).SetUint64(st.msg.Gas()), st.gasPrice)
-	if state.GetBalance(sender.Address()).Cmp(mgval) < 0 {
+	if st.state.GetBalance(st.msg.From()).Cmp(mgval) < 0 {
 		return errInsufficientBalanceForGas
 	}
 	if err := st.gp.SubGas(st.msg.Gas()); err != nil {
@@ -180,20 +160,17 @@ func (st *StateTransition) buyGas() error {
 	st.gas += st.msg.Gas()
 
 	st.initialGas = st.msg.Gas()
-	state.SubBalance(sender.Address(), mgval)
+	st.state.SubBalance(st.msg.From(), mgval)
 	return nil
 }
 
 func (st *StateTransition) preCheck() error {
-	msg := st.msg
-	sender := st.from()
-
-	// Make sure this transaction's nonce is correct
-	if msg.CheckNonce() {
-		nonce := st.state.GetNonce(sender.Address())
-		if nonce < msg.Nonce() {
+	// Make sure this transaction's nonce is correct.
+	if st.msg.CheckNonce() {
+		nonce := st.state.GetNonce(st.msg.From())
+		if nonce < st.msg.Nonce() {
 			return ErrNonceTooHigh
-		} else if nonce > msg.Nonce() {
+		} else if nonce > st.msg.Nonce() {
 			return ErrNonceTooLow
 		}
 	}
@@ -208,8 +185,7 @@ func (st *StateTransition) TransitionDb() (ret []byte, usedGas uint64, failed bo
 		return
 	}
 	msg := st.msg
-	sender := st.from() // err checked in preCheck
-
+	sender := vm.AccountRef(msg.From())
 	homestead := st.evm.ChainConfig().IsHomestead(st.evm.BlockNumber)
 	contractCreation := msg.To() == nil
 
@@ -233,8 +209,8 @@ func (st *StateTransition) TransitionDb() (ret []byte, usedGas uint64, failed bo
 		ret, _, st.gas, vmerr = evm.Create(sender, st.data, st.gas, st.value)
 	} else {
 		// Increment the nonce for the next transaction
-		st.state.SetNonce(sender.Address(), st.state.GetNonce(sender.Address())+1)
-		ret, st.gas, vmerr = evm.Call(sender, st.to().Address(), st.data, st.gas, st.value)
+		st.state.SetNonce(msg.From(), st.state.GetNonce(sender.Address())+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)
@@ -260,10 +236,8 @@ func (st *StateTransition) refundGas() {
 	st.gas += refund
 
 	// Return ETH for remaining gas, exchanged at the original rate.
-	sender := st.from()
-
 	remaining := new(big.Int).Mul(new(big.Int).SetUint64(st.gas), st.gasPrice)
-	st.state.AddBalance(sender.Address(), remaining)
+	st.state.AddBalance(st.msg.From(), remaining)
 
 	// Also return remaining gas to the block gas counter so it is
 	// available for the next transaction.