eth/txtracker: gate credit on pre-slot delivery

Add a per-entry arrival timestamp at NotifyAccepted time and skip inclusion
and finalization credit when the delivery was at or after the slot of the
inclusion block. This prevents a peer that learned a tx from the
just-propagated block (or any post-slot source) from harvesting credit it
didn't earn through genuine pre-slot relay work.

Does not defeat builder-feed peers that deliver within the feed's lead
time before slot start; but that's also not fundamentally different from
sending to the mempool in the first place.

Signed-off-by: Csaba Kiraly <csaba.kiraly@gmail.com>

eth/txtracker/tracker.go

@@ -28,6 +28,7 @@ package txtracker
 
 import (
 	"sync"
+	"time"
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core"
@@ -67,11 +68,20 @@ type peerStats struct {
 	recentIncluded  float64
 }
 
+// txEntry tracks the deliverer of a transaction and when delivery was
+// recorded. addedAt is unix seconds; it is compared against block.Time()
+// to suppress credit for txs delivered at or after the slot of their
+// inclusion block (e.g., re-broadcasts of just-mined txs).
+type txEntry struct {
+	peer    string
+	addedAt uint64
+}
+
 // Tracker records which peer delivered each transaction and credits peers
 // when their transactions appear on chain.
 type Tracker struct {
 	mu    sync.Mutex
-	txs   map[common.Hash]string // hash → deliverer peer ID
+	txs   map[common.Hash]txEntry // hash → deliverer + arrival time
 	peers map[string]*peerStats
 	order []common.Hash // insertion order for LRU eviction
 
@@ -83,16 +93,18 @@ type Tracker struct {
 	quit     chan struct{}
 	stopOnce sync.Once
 	step     chan struct{} // test sync: sent after each event is processed
+	now      func() uint64 // unix-seconds clock; overridable in tests
 	wg       sync.WaitGroup
 }
 
 // New creates a new tracker.
 func New() *Tracker {
 	return &Tracker{
-		txs:   make(map[common.Hash]string),
+		txs:   make(map[common.Hash]txEntry),
 		peers: make(map[string]*peerStats),
 		quit:  make(chan struct{}),
 		step:  make(chan struct{}, 1),
+		now:   func() uint64 { return uint64(time.Now().Unix()) },
 	}
 }
 
@@ -136,11 +148,12 @@ func (t *Tracker) NotifyAccepted(peer string, hashes []common.Hash) {
 	t.mu.Lock()
 	defer t.mu.Unlock()
 
+	addedAt := t.now()
 	for _, hash := range hashes {
 		if _, ok := t.txs[hash]; ok {
 			continue // already tracked, keep first deliverer
 		}
-		t.txs[hash] = peer
+		t.txs[hash] = txEntry{peer: peer, addedAt: addedAt}
 		t.order = append(t.order, hash)
 	}
 	// Ensure the delivering peer has a stats entry.
@@ -206,11 +219,17 @@ func (t *Tracker) handleChainHead(ev core.ChainHeadEvent) {
 	defer t.mu.Unlock()
 
 	// Count per-peer inclusions in this block for the inclusion EMA.
+	// Skip txs whose delivery arrived at or after this block's slot — those
+	// are likely post-slot re-broadcasts of an already-mined tx, not genuine
+	// relay work.
+	blockTime := block.Time()
 	blockIncl := make(map[string]int)
 	for _, tx := range block.Transactions() {
-		if peer := t.txs[tx.Hash()]; peer != "" {
-			blockIncl[peer]++
+		entry, ok := t.txs[tx.Hash()]
+		if !ok || entry.addedAt >= blockTime {
+			continue
 		}
+		blockIncl[entry.peer]++
 	}
 	// Accumulate per-peer finalization credits over the newly-finalized
 	// range (possibly zero blocks). Only counts peers still tracked.
@@ -245,15 +264,16 @@ func (t *Tracker) collectFinalizationCredits() map[string]int {
 		if block == nil {
 			continue
 		}
+		blockTime := block.Time()
 		for _, tx := range block.Transactions() {
-			peer := t.txs[tx.Hash()]
-			if peer == "" {
-				continue
+			entry, ok := t.txs[tx.Hash()]
+			if !ok || entry.addedAt >= blockTime {
+				continue // unknown, or post-slot re-broadcast
 			}
-			if _, ok := t.peers[peer]; !ok {
+			if _, ok := t.peers[entry.peer]; !ok {
 				continue // peer disconnected, skip credit
 			}
-			credits[peer]++
+			credits[entry.peer]++
 		}
 	}
 	if total := sumCounts(credits); total > 0 {

eth/txtracker/tracker_test.go

@@ -90,12 +90,20 @@ func (c *mockChain) addBlock(num uint64, txs []*types.Transaction) *types.Block
 // for reorg tests). If canonical is true, the block becomes the canonical
 // block for that height (looked up by GetBlockByNumber).
 func (c *mockChain) addBlockAtHeight(num, salt uint64, txs []*types.Transaction, canonical bool) *types.Block {
+	return c.addBlockAtHeightWithTime(num, salt, txs, canonical, uint64(time.Now().Unix()+3600))
+}
+
+// addBlockAtHeightWithTime is like addBlockAtHeight but takes an explicit
+// block time. Used by the pre-slot gate test, which needs a block whose
+// slot start is BEFORE the moment NotifyAccepted recorded its tx.
+func (c *mockChain) addBlockAtHeightWithTime(num, salt uint64, txs []*types.Transaction, canonical bool, blockTime uint64) *types.Block {
 	c.mu.Lock()
 	defer c.mu.Unlock()
 	// Mix salt into Extra so siblings at the same height get distinct hashes.
 	header := &types.Header{
 		Number: new(big.Int).SetUint64(num),
 		Extra:  big.NewInt(int64(salt)).Bytes(),
+		Time:   blockTime,
 	}
 	block := types.NewBlock(header, &types.Body{Transactions: txs}, nil, trie.NewListHasher())
 	c.blocksByHash[block.Hash()] = block
@@ -189,8 +197,8 @@ func TestNotifyReceived(t *testing.T) {
 		t.Fatalf("expected order length 3, got %d", len(tr.order))
 	}
 	for i, h := range hashes {
-		if got := tr.txs[h]; got != "peerA" {
-			t.Fatalf("tx %d: expected deliverer=peerA, got %q", i, got)
+		if got := tr.txs[h]; got.peer != "peerA" {
+			t.Fatalf("tx %d: expected deliverer=peerA, got %q", i, got.peer)
 		}
 		if tr.order[i] != h {
 			t.Fatalf("order[%d] mismatch", i)
@@ -454,3 +462,48 @@ func TestRecentFinalizedDecays(t *testing.T) {
 		t.Fatalf("expected RecentFinalized to decay, got %f >= peak %f", after, peak)
 	}
 }
+
+// TestPreSlotGate verifies that a tx delivered at or after the slot of its
+// inclusion block earns no credit. This blocks the simple
+// post-block-propagation re-broadcast attribution attack: a peer that
+// learns a tx from the just-mined block and re-broadcasts it to our pool
+// should not gain credit when that block is processed. The finalization
+// path applies the same gate (entry.addedAt >= blockTime) and is exercised
+// by the existing TestFinalization with the new clock semantics.
+func TestPreSlotGate(t *testing.T) {
+	tr := New()
+	chain := newMockChain()
+	tr.Start(chain)
+	defer tr.Stop()
+
+	// Pin the tracker's clock so NotifyAccepted records a known addedAt.
+	const delivery = uint64(1_000_000)
+	tr.now = func() uint64 { return delivery }
+
+	// peerA delivers two txs at the same instant.
+	preTx := makeTx(1)
+	postTx := makeTx(2)
+	tr.NotifyAccepted("peerA", []common.Hash{preTx.Hash(), postTx.Hash()})
+
+	// Block 1: slot strictly AFTER delivery — pre-slot, credit allowed.
+	chain.addBlockAtHeightWithTime(1, 1, []*types.Transaction{preTx}, true, delivery+100)
+	chain.sendHead(1)
+	waitStep(t, tr)
+
+	preEMA := tr.GetAllPeerStats()["peerA"].RecentIncluded
+	if preEMA <= 0 {
+		t.Fatalf("expected RecentIncluded>0 after pre-slot delivery, got %f", preEMA)
+	}
+
+	// Block 2: slot strictly BEFORE delivery — post-slot, must NOT credit.
+	chain.addBlockAtHeightWithTime(2, 2, []*types.Transaction{postTx}, true, delivery-1)
+	chain.sendHead(2)
+	waitStep(t, tr)
+
+	// With the gate, only EMA decay occurs (no contribution this block).
+	// Without the gate, RecentIncluded would have ticked up again.
+	after := tr.GetAllPeerStats()["peerA"].RecentIncluded
+	if after >= preEMA {
+		t.Fatalf("expected EMA to decay (no credit for post-slot tx), got %f >= preEMA %f", after, preEMA)
+	}
+}