From d7bdbd7488644f0aaeee5cdcdc119c863f199f72 Mon Sep 17 00:00:00 2001
From: Daniel Choi <13338103+araskachoi@users.noreply.github.com>
Date: Fri, 8 Jan 2021 17:44:50 -0800
Subject: [PATCH] Fix nonce issue for replay attack (#692)

* fix nonce issue for replay attack

* fix lint

* add to changelog
---
 CHANGELOG.md              |  2 ++
 app/ante/eth.go           |  2 +-
 rpc/namespaces/eth/api.go | 14 +++++++-------
 3 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index eefabf28..263afeda 100644
--- a/CHANGELOG.md
+++ b/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.
 
diff --git a/app/ante/eth.go b/app/ante/eth.go
index 6f4f6a1e..b367f0bb 100644
--- a/app/ante/eth.go
+++ b/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,
diff --git a/rpc/namespaces/eth/api.go b/rpc/namespaces/eth/api.go
index fb7ff5d5..69baf413 100644
--- a/rpc/namespaces/eth/api.go
+++ b/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")