core: bugfix state change race condition in txpool (#3412)

The transaction pool keeps track of the current nonce in its local pendingState. When a
new block comes in the pendingState is reset. During the reset it fetches multiple times
the current state through the use of the currentState callback. When a second block comes
in during the reset its possible that the state changes during the reset. If that block
holds transactions that are currently in the pool the local pendingState that is used to
determine nonces can get out of sync.

1 files changed, 8 insertions, 3 deletions

diff --git a/eth/api_backend.go b/eth/api_backend.go
index b95ef79c5..f33b6f7e1 100644
--- a/eth/api_backend.go
+++ b/eth/api_backend.go
@@ -131,15 +131,20 @@ func (b *EthApiBackend) RemoveTx(txHash common.Hash) {
 	b.eth.txPool.Remove(txHash)
 }
 
-func (b *EthApiBackend) GetPoolTransactions() types.Transactions {
+func (b *EthApiBackend) GetPoolTransactions() (types.Transactions, error) {
 	b.eth.txMu.Lock()
 	defer b.eth.txMu.Unlock()
 
+	pending, err := b.eth.txPool.Pending()
+	if err != nil {
+		return nil, err
+	}
+
 	var txs types.Transactions
-	for _, batch := range b.eth.txPool.Pending() {
+	for _, batch := range pending {
 		txs = append(txs, batch...)
 	}
-	return txs
+	return txs, nil
 }
 
 func (b *EthApiBackend) GetPoolTransaction(hash common.Hash) *types.Transaction {