core/txpool: implement additional DoS defenses (#26648)

This adds two new rules to the transaction pool:

- A future transaction can not evict a pending transaction.
- A transaction can not overspend available funds of a sender.

---

Co-authored-by: dwn1998 <42262393+dwn1998@users.noreply.github.com>
Co-authored-by: Martin Holst Swende <martin@swende.se>

Author: 3 people

core/txpool/list.go

@@ -254,17 +254,19 @@ type list struct {
 	strict bool       // Whether nonces are strictly continuous or not
 	txs    *sortedMap // Heap indexed sorted hash map of the transactions
 
-	costcap *big.Int // Price of the highest costing transaction (reset only if exceeds balance)
-	gascap  uint64   // Gas limit of the highest spending transaction (reset only if exceeds block limit)
+	costcap   *big.Int // Price of the highest costing transaction (reset only if exceeds balance)
+	gascap    uint64   // Gas limit of the highest spending transaction (reset only if exceeds block limit)
+	totalcost *big.Int // Total cost of all transactions in the list
 }
 
 // newList create a new transaction list for maintaining nonce-indexable fast,
 // gapped, sortable transaction lists.
 func newList(strict bool) *list {
 	return &list{
-		strict:  strict,
-		txs:     newSortedMap(),
-		costcap: new(big.Int),
+		strict:    strict,
+		txs:       newSortedMap(),
+		costcap:   new(big.Int),
+		totalcost: new(big.Int),
 	}
 }
 
@@ -302,7 +304,11 @@ 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
+	l.totalcost.Add(l.totalcost, tx.Cost())
 	// Otherwise overwrite the old transaction with the current one
 	l.txs.Put(tx)
 	if cost := tx.Cost(); l.costcap.Cmp(cost) < 0 {
@@ -318,7 +324,9 @@ func (l *list) Add(tx *types.Transaction, priceBump uint64) (bool, *types.Transa
 // provided threshold. Every removed transaction is returned for any post-removal
 // maintenance.
 func (l *list) Forward(threshold uint64) types.Transactions {
-	return l.txs.Forward(threshold)
+	txs := l.txs.Forward(threshold)
+	l.subTotalCost(txs)
+	return txs
 }
 
 // Filter removes all transactions from the list with a cost or gas limit higher
@@ -357,14 +365,19 @@ func (l *list) Filter(costLimit *big.Int, gasLimit uint64) (types.Transactions,
 		}
 		invalids = l.txs.filter(func(tx *types.Transaction) bool { return tx.Nonce() > lowest })
 	}
+	// Reset total cost
+	l.subTotalCost(removed)
+	l.subTotalCost(invalids)
 	l.txs.reheap()
 	return removed, invalids
 }
 
 // Cap places a hard limit on the number of items, returning all transactions
 // exceeding that limit.
 func (l *list) Cap(threshold int) types.Transactions {
-	return l.txs.Cap(threshold)
+	txs := l.txs.Cap(threshold)
+	l.subTotalCost(txs)
+	return txs
 }
 
 // Remove deletes a transaction from the maintained list, returning whether the
@@ -376,9 +389,12 @@ func (l *list) Remove(tx *types.Transaction) (bool, types.Transactions) {
 	if removed := l.txs.Remove(nonce); !removed {
 		return false, nil
 	}
+	l.subTotalCost([]*types.Transaction{tx})
 	// In strict mode, filter out non-executable transactions
 	if l.strict {
-		return true, l.txs.Filter(func(tx *types.Transaction) bool { return tx.Nonce() > nonce })
+		txs := l.txs.Filter(func(tx *types.Transaction) bool { return tx.Nonce() > nonce })
+		l.subTotalCost(txs)
+		return true, txs
 	}
 	return true, nil
 }
@@ -391,7 +407,9 @@ func (l *list) Remove(tx *types.Transaction) (bool, types.Transactions) {
 // prevent getting into and invalid state. This is not something that should ever
 // happen but better to be self correcting than failing!
 func (l *list) Ready(start uint64) types.Transactions {
-	return l.txs.Ready(start)
+	txs := l.txs.Ready(start)
+	l.subTotalCost(txs)
+	return txs
 }
 
 // Len returns the length of the transaction list.
@@ -417,6 +435,14 @@ func (l *list) LastElement() *types.Transaction {
 	return l.txs.LastElement()
 }
 
+// subTotalCost subtracts the cost of the given transactions from the
+// total cost of all transactions.
+func (l *list) subTotalCost(txs []*types.Transaction) {
+	for _, tx := range txs {
+		l.totalcost.Sub(l.totalcost, tx.Cost())
+	}
+}
+
 // priceHeap is a heap.Interface implementation over transactions for retrieving
 // price-sorted transactions to discard when the pool fills up. If baseFee is set
 // then the heap is sorted based on the effective tip based on the given base fee.
@@ -561,6 +587,7 @@ func (l *pricedList) underpricedFor(h *priceHeap, tx *types.Transaction) bool {
 
 // Discard finds a number of most underpriced transactions, removes them from the
 // priced list and returns them for further removal from the entire pool.
+// If noPending is set to true, we will only consider the floating list
 //
 // Note local transaction won't be considered for eviction.
 func (l *pricedList) Discard(slots int, force bool) (types.Transactions, bool) {

core/txpool/txpool.go

@@ -17,6 +17,7 @@
 package txpool
 
 import (
+	"container/heap"
 	"errors"
 	"fmt"
 	"math"
@@ -87,6 +88,14 @@ var (
 	// than some meaningful limit a user might use. This is not a consensus error
 	// making the transaction invalid, rather a DOS protection.
 	ErrOversizedData = errors.New("oversized data")
+
+	// ErrFutureReplacePending is returned if a future transaction replaces a pending
+	// transaction. Future transactions should only be able to replace other future transactions.
+	ErrFutureReplacePending = errors.New("future transaction tries to replace pending")
+
+	// ErrOverdraft is returned if a transaction would cause the senders balance to go negative
+	// thus invalidating a potential large number of transactions.
+	ErrOverdraft = errors.New("transaction would cause overdraft")
 )
 
 var (
@@ -639,9 +648,25 @@ func (pool *TxPool) validateTx(tx *types.Transaction, local bool) error {
 	}
 	// Transactor should have enough funds to cover the costs
 	// cost == V + GP * GL
-	if pool.currentState.GetBalance(from).Cmp(tx.Cost()) < 0 {
+	balance := pool.currentState.GetBalance(from)
+	if balance.Cmp(tx.Cost()) < 0 {
 		return core.ErrInsufficientFunds
 	}
+
+	// Verify that replacing transactions will not result in overdraft
+	list := pool.pending[from]
+	if list != nil { // Sender already has pending txs
+		sum := new(big.Int).Add(tx.Cost(), list.totalcost)
+		if repl := list.txs.Get(tx.Nonce()); repl != nil {
+			// Deduct the cost of a transaction replaced by this
+			sum.Sub(sum, repl.Cost())
+		}
+		if balance.Cmp(sum) < 0 {
+			log.Trace("Replacing transactions would overdraft", "sender", from, "balance", pool.currentState.GetBalance(from), "required", sum)
+			return ErrOverdraft
+		}
+	}
+
 	// Ensure the transaction has more gas than the basic tx fee.
 	intrGas, err := core.IntrinsicGas(tx.Data(), tx.AccessList(), tx.To() == nil, true, pool.istanbul, pool.shanghai)
 	if err != nil {
@@ -678,6 +703,10 @@ func (pool *TxPool) add(tx *types.Transaction, local bool) (replaced bool, err e
 		invalidTxMeter.Mark(1)
 		return false, err
 	}
+
+	// already validated by this point
+	from, _ := types.Sender(pool.signer, tx)
+
 	// If the transaction pool is full, discard underpriced transactions
 	if uint64(pool.all.Slots()+numSlots(tx)) > pool.config.GlobalSlots+pool.config.GlobalQueue {
 		// If the new transaction is underpriced, don't accept it
@@ -686,6 +715,7 @@ func (pool *TxPool) add(tx *types.Transaction, local bool) (replaced bool, err e
 			underpricedTxMeter.Mark(1)
 			return false, ErrUnderpriced
 		}
+
 		// We're about to replace a transaction. The reorg does a more thorough
 		// analysis of what to remove and how, but it runs async. We don't want to
 		// do too many replacements between reorg-runs, so we cap the number of
@@ -706,17 +736,37 @@ func (pool *TxPool) add(tx *types.Transaction, local bool) (replaced bool, err e
 			overflowedTxMeter.Mark(1)
 			return false, ErrTxPoolOverflow
 		}
-		// Bump the counter of rejections-since-reorg
-		pool.changesSinceReorg += len(drop)
+
+		// If the new transaction is a future transaction it should never churn pending transactions
+		if pool.isFuture(from, tx) {
+			var replacesPending bool
+			for _, dropTx := range drop {
+				dropSender, _ := types.Sender(pool.signer, dropTx)
+				if list := pool.pending[dropSender]; list != nil && list.Overlaps(dropTx) {
+					replacesPending = true
+					break
+				}
+			}
+			// Add all transactions back to the priced queue
+			if replacesPending {
+				for _, dropTx := range drop {
+					heap.Push(&pool.priced.urgent, dropTx)
+				}
+				log.Trace("Discarding future transaction replacing pending tx", "hash", hash)
+				return false, ErrFutureReplacePending
+			}
+		}
+
 		// Kick out the underpriced remote transactions.
 		for _, tx := range drop {
 			log.Trace("Discarding freshly underpriced transaction", "hash", tx.Hash(), "gasTipCap", tx.GasTipCap(), "gasFeeCap", tx.GasFeeCap())
 			underpricedTxMeter.Mark(1)
-			pool.removeTx(tx.Hash(), false)
+			dropped := pool.removeTx(tx.Hash(), false)
+			pool.changesSinceReorg += dropped
 		}
 	}
+
 	// Try to replace an existing transaction in the pending pool
-	from, _ := types.Sender(pool.signer, tx) // already validated
 	if list := pool.pending[from]; list != nil && list.Overlaps(tx) {
 		// Nonce already pending, check if required price bump is met
 		inserted, old := list.Add(tx, pool.config.PriceBump)
@@ -760,6 +810,20 @@ func (pool *TxPool) add(tx *types.Transaction, local bool) (replaced bool, err e
 	return replaced, nil
 }
 
+// isFuture reports whether the given transaction is immediately executable.
+func (pool *TxPool) isFuture(from common.Address, tx *types.Transaction) bool {
+	list := pool.pending[from]
+	if list == nil {
+		return pool.pendingNonces.get(from) != tx.Nonce()
+	}
+	// Sender has pending transactions.
+	if old := list.txs.Get(tx.Nonce()); old != nil {
+		return false // It replaces a pending transaction.
+	}
+	// Not replacing, check if parent nonce exists in pending.
+	return list.txs.Get(tx.Nonce()-1) == nil
+}
+
 // enqueueTx inserts a new transaction into the non-executable transaction queue.
 //
 // Note, this method assumes the pool lock is held!
@@ -996,11 +1060,12 @@ func (pool *TxPool) Has(hash common.Hash) bool {
 
 // removeTx removes a single transaction from the queue, moving all subsequent
 // transactions back to the future queue.
-func (pool *TxPool) removeTx(hash common.Hash, outofbound bool) {
+// Returns the number of transactions removed from the pending queue.
+func (pool *TxPool) removeTx(hash common.Hash, outofbound bool) int {
 	// Fetch the transaction we wish to delete
 	tx := pool.all.Get(hash)
 	if tx == nil {
-		return
+		return 0
 	}
 	addr, _ := types.Sender(pool.signer, tx) // already validated during insertion
 
@@ -1028,7 +1093,7 @@ func (pool *TxPool) removeTx(hash common.Hash, outofbound bool) {
 			pool.pendingNonces.setIfLower(addr, tx.Nonce())
 			// Reduce the pending counter
 			pendingGauge.Dec(int64(1 + len(invalids)))
-			return
+			return 1 + len(invalids)
 		}
 	}
 	// Transaction is in the future queue
@@ -1042,6 +1107,7 @@ func (pool *TxPool) removeTx(hash common.Hash, outofbound bool) {
 			delete(pool.beats, addr)
 		}
 	}
+	return 0
 }
 
 // requestReset requests a pool reset to the new head block.