core/txpool: add sanity overflow check

[MariusVanDerWijden]

Adds a sanity check in the transaction pool

Co-authored-by @rjl493456442

[rjl493456442]

diff --git a/core/txpool/legacypool/list.go b/core/txpool/legacypool/list.go
index e5c48d538d..85008e3310 100644
--- a/core/txpool/legacypool/list.go
+++ b/core/txpool/legacypool/list.go
@@ -323,8 +323,6 @@ func (l *list) Add(tx *types.Transaction, priceBump uint64) (bool, *types.Transa
         if tx.GasFeeCapIntCmp(thresholdFeeCap) < 0 || tx.GasTipCapIntCmp(thresholdTip) < 0 {
             return false, nil
         }
-        // Old is being replaced, subtract old cost
-        l.subTotalCost([]*types.Transaction{old})
     }
     // Add new tx cost to totalcost
     cost, overflow := uint256.FromBig(tx.Cost())
@@ -337,6 +335,10 @@ func (l *list) Add(tx *types.Transaction, priceBump uint64) (bool, *types.Transa
     }
     l.totalcost = total
 
+    // Old is being replaced, subtract old cost
+    if old != nil {
+        l.subTotalCost([]*types.Transaction{old})
+    }
     // Otherwise overwrite the old transaction with the current one
     l.txs.Put(tx)
     if l.costcap.Cmp(cost) < 0 {

[MariusVanDerWijden]

PTAL @rjl493456442

[rjl493456442]

The old can be nil. l.subTotalCost([]*types.Transaction{nil}) will panic, isn't it?

[MariusVanDerWijden]

yes good catch