Fix nonce issue for replay attack (#692)

* fix nonce issue for replay attack

* fix lint

* add to changelog

Author: araskachoi

CHANGELOG.md

@@ -44,6 +44,8 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 ### Bug Fixes
 
+* (evm) [\#687](https://github.com/cosmos/ethermint/issues/687) Fix nonce check to explicitly check for the correct nonce, rather than a simple 'greater than' comparison. 
+* (api) [\#687](https://github.com/cosmos/ethermint/issues/687) Returns error for a transaction with an incorrect nonce. 
 * (evm) [\#674](https://github.com/cosmos/ethermint/issues/674) Reset all cache after account data has been committed in `EndBlock` to make sure every node state consistent.
 * (evm) [\#672](https://github.com/cosmos/ethermint/issues/672) Fix panic of `wrong Block.Header.AppHash` when restart a node with snapshot.
 

app/ante/eth.go

@@ -257,7 +257,7 @@ func (nvd NonceVerificationDecorator) AnteHandle(ctx sdk.Context, tx sdk.Tx, sim
 	// if multiple transactions are submitted in succession with increasing nonces,
 	// all will be rejected except the first, since the first needs to be included in a block
 	// before the sequence increments
-	if msgEthTx.Data.AccountNonce < seq {
+	if msgEthTx.Data.AccountNonce != seq {
 		return ctx, sdkerrors.Wrapf(
 			sdkerrors.ErrInvalidSequence,
 			"invalid nonce; got %d, expected %d", msgEthTx.Data.AccountNonce, seq,

rpc/namespaces/eth/api.go

@@ -1000,16 +1000,16 @@ func (api *PublicEthereumAPI) generateFromArgs(args rpctypes.SendTxArgs) (*evmty
 		gasPrice = big.NewInt(ethermint.DefaultGasPrice)
 	}
 
-	if args.Nonce == nil {
-		// get the nonce from the account retriever and the pending transactions
-		nonce, err = api.accountNonce(api.clientCtx, args.From, true)
-	} else {
-		nonce = (uint64)(*args.Nonce)
-	}
-
+	// get the nonce from the account retriever and the pending transactions
+	nonce, err = api.accountNonce(api.clientCtx, args.From, true)
 	if err != nil {
 		return nil, err
 	}
+	if args.Nonce != nil {
+		if nonce != (uint64)(*args.Nonce) {
+			return nil, fmt.Errorf(fmt.Sprintf("invalid nonce; got %d, expected %d", (uint64)(*args.Nonce), nonce))
+		}
+	}
 
 	if args.Data != nil && args.Input != nil && !bytes.Equal(*args.Data, *args.Input) {
 		return nil, errors.New("both 'data' and 'input' are set and not equal. Please use 'input' to pass transaction call data")