discovery: obtain channelMtx before doing any DB calls in handleChannelUpdate

discovery/gossiper.go

@@ -2997,6 +2997,12 @@ func (d *AuthenticatedGossiper) handleChanUpdate(nMsg *networkMsg,
 		graphScid = upd.ShortChannelID
 	}
 
+	// We make sure to obtain the mutex for this channel ID before we access
+	// the database. This ensures the state we read from the database has
+	// not changed between this point and when we call UpdateEdge() later.
+	d.channelMtx.Lock(graphScid.ToUint64())
+	defer d.channelMtx.Unlock(graphScid.ToUint64())
+
 	if d.cfg.Graph.IsStaleEdgePolicy(
 		graphScid, timestamp, upd.ChannelFlags,
 	) {
@@ -3029,14 +3035,6 @@ func (d *AuthenticatedGossiper) handleChanUpdate(nMsg *networkMsg,
 	// Get the node pub key as far since we don't have it in the channel
 	// update announcement message. We'll need this to properly verify the
 	// message's signature.
-	//
-	// We make sure to obtain the mutex for this channel ID before we
-	// access the database. This ensures the state we read from the
-	// database has not changed between this point and when we call
-	// UpdateEdge() later.
-	d.channelMtx.Lock(graphScid.ToUint64())
-	defer d.channelMtx.Unlock(graphScid.ToUint64())
-
 	chanInfo, e1, e2, err := d.cfg.Graph.GetChannelByID(graphScid)
 	switch {
 	// No error, break.

discovery/gossiper_test.go

@@ -76,7 +76,9 @@ var (
 	rebroadcastInterval = time.Hour * 1000000
 )
 
+// TODO(elle): replace mockGraphSource with testify.Mock.
 type mockGraphSource struct {
+	t          *testing.T
 	bestHeight uint32
 
 	mu            sync.Mutex
@@ -85,15 +87,22 @@ type mockGraphSource struct {
 	edges         map[uint64][]models.ChannelEdgePolicy
 	zombies       map[uint64][][33]byte
 	chansToReject map[uint64]struct{}
+
+	updateEdgeCount     int
+	pauseGetChannelByID chan chan struct{}
 }
 
-func newMockRouter(height uint32) *mockGraphSource {
+func newMockRouter(t *testing.T, height uint32) *mockGraphSource {
 	return &mockGraphSource{
-		bestHeight:    height,
-		infos:         make(map[uint64]models.ChannelEdgeInfo),
-		edges:         make(map[uint64][]models.ChannelEdgePolicy),
-		zombies:       make(map[uint64][][33]byte),
-		chansToReject: make(map[uint64]struct{}),
+		t:          t,
+		bestHeight: height,
+		infos:      make(map[uint64]models.ChannelEdgeInfo),
+		edges: make(
+			map[uint64][]models.ChannelEdgePolicy,
+		),
+		zombies:             make(map[uint64][][33]byte),
+		chansToReject:       make(map[uint64]struct{}),
+		pauseGetChannelByID: make(chan chan struct{}, 1),
 	}
 }
 
@@ -155,7 +164,10 @@ func (r *mockGraphSource) UpdateEdge(edge *models.ChannelEdgePolicy,
 	_ ...batch.SchedulerOption) error {
 
 	r.mu.Lock()
-	defer r.mu.Unlock()
+	defer func() {
+		r.updateEdgeCount++
+		r.mu.Unlock()
+	}()
 
 	if len(r.edges[edge.ChannelID]) == 0 {
 		r.edges[edge.ChannelID] = make([]models.ChannelEdgePolicy, 2)
@@ -234,6 +246,18 @@ func (r *mockGraphSource) GetChannelByID(chanID lnwire.ShortChannelID) (
 	*models.ChannelEdgePolicy,
 	*models.ChannelEdgePolicy, error) {
 
+	select {
+	// Check if a pause request channel has been loaded. If one has, then we
+	// wait for it to be closed before continuing.
+	case pauseChan := <-r.pauseGetChannelByID:
+		select {
+		case <-pauseChan:
+		case <-time.After(time.Second * 30):
+			r.t.Fatal("timeout waiting for pause channel")
+		}
+	default:
+	}
+
 	r.mu.Lock()
 	defer r.mu.Unlock()
 
@@ -874,7 +898,7 @@ func createTestCtx(t *testing.T, startHeight uint32, isChanPeer bool) (
 	// any p2p functionality, the peer send and switch send,
 	// broadcast functions won't be populated.
 	notifier := newMockNotifier()
-	router := newMockRouter(startHeight)
+	router := newMockRouter(t, startHeight)
 	chain := &lnmock.MockChain{}
 	t.Cleanup(func() {
 		chain.AssertExpectations(t)
@@ -3977,6 +4001,202 @@ func TestBroadcastAnnsAfterGraphSynced(t *testing.T) {
 	assertBroadcast(chanAnn2, true, true)
 }
 
+// TestRateLimitDeDup tests that if we get the same channel update in very
+// quick succession, then these updates should not be individually considered
+// in our rate limiting logic.
+//
+// NOTE: this only tests the deduplication logic. The main rate limiting logic
+// is tested by TestRateLimitChannelUpdates.
+func TestRateLimitDeDup(t *testing.T) {
+	t.Parallel()
+
+	// Create our test harness.
+	const blockHeight = 100
+	ctx, err := createTestCtx(t, blockHeight, false)
+	require.NoError(t, err, "can't create context")
+	ctx.gossiper.cfg.RebroadcastInterval = time.Hour
+
+	var findBaseByAliasCount atomic.Int32
+	ctx.gossiper.cfg.FindBaseByAlias = func(alias lnwire.ShortChannelID) (
+		lnwire.ShortChannelID, error) {
+
+		findBaseByAliasCount.Add(1)
+
+		return lnwire.ShortChannelID{}, fmt.Errorf("none")
+	}
+
+	getUpdateEdgeCount := func() int {
+		ctx.router.mu.Lock()
+		defer ctx.router.mu.Unlock()
+
+		return ctx.router.updateEdgeCount
+	}
+
+	// We set the burst to 2 here. The very first update should not count
+	// towards this _and_ any duplicates should also not count towards it.
+	ctx.gossiper.cfg.MaxChannelUpdateBurst = 2
+	ctx.gossiper.cfg.ChannelUpdateInterval = time.Minute
+
+	// The graph should start empty.
+	require.Empty(t, ctx.router.infos)
+	require.Empty(t, ctx.router.edges)
+
+	// We'll create a batch of signed announcements, including updates for
+	// both sides, for a channel and process them. They should all be
+	// forwarded as this is our first time learning about the channel.
+	batch, err := ctx.createRemoteAnnouncements(blockHeight)
+	require.NoError(t, err)
+
+	nodePeer1 := &mockPeer{
+		remoteKeyPriv1.PubKey(), nil, nil, atomic.Bool{},
+	}
+	select {
+	case err := <-ctx.gossiper.ProcessRemoteAnnouncement(
+		batch.chanAnn, nodePeer1,
+	):
+		require.NoError(t, err)
+	case <-time.After(time.Second):
+		t.Fatal("remote announcement not processed")
+	}
+
+	select {
+	case err := <-ctx.gossiper.ProcessRemoteAnnouncement(
+		batch.chanUpdAnn1, nodePeer1,
+	):
+		require.NoError(t, err)
+	case <-time.After(time.Second):
+		t.Fatal("remote announcement not processed")
+	}
+
+	nodePeer2 := &mockPeer{
+		remoteKeyPriv2.PubKey(), nil, nil, atomic.Bool{},
+	}
+	select {
+	case err := <-ctx.gossiper.ProcessRemoteAnnouncement(
+		batch.chanUpdAnn2, nodePeer2,
+	):
+		require.NoError(t, err)
+	case <-time.After(time.Second):
+		t.Fatal("remote announcement not processed")
+	}
+
+	timeout := time.After(2 * trickleDelay)
+	for i := 0; i < 3; i++ {
+		select {
+		case <-ctx.broadcastedMessage:
+		case <-timeout:
+			t.Fatal("expected announcement to be broadcast")
+		}
+	}
+
+	shortChanID := batch.chanAnn.ShortChannelID.ToUint64()
+	require.Contains(t, ctx.router.infos, shortChanID)
+	require.Contains(t, ctx.router.edges, shortChanID)
+
+	// Before we send anymore updates, we want to let our test harness
+	// hang during GetChannelByID so that we can ensure that two threads are
+	// waiting for the chan.
+	pause := make(chan struct{})
+	ctx.router.pauseGetChannelByID <- pause
+
+	// Take note of how many times FindBaseByAlias has been called.
+	// It should be 2 since we have processed two channel updates.
+	require.EqualValues(t, 2, findBaseByAliasCount.Load())
+
+	// The same is expected for the UpdateEdge call.
+	require.EqualValues(t, 2, getUpdateEdgeCount())
+
+	update := *batch.chanUpdAnn1
+
+	// refreshUpdate is a helper that helps us ensure that the update
+	// is not seen as stale or as a keep-alive.
+	refreshUpdate := func() {
+		update.Timestamp++
+		update.BaseFee++
+		require.NoError(t, signUpdate(remoteKeyPriv1, &update))
+	}
+
+	refreshUpdate()
+
+	// Ok, now we will send the same channel update twice in quick
+	// succession. We wait for both to have hit the FindBaseByAlias check
+	// before we un-pause the GetChannelByID call.
+	go func() {
+		ctx.gossiper.ProcessRemoteAnnouncement(&update, nodePeer1)
+	}()
+	go func() {
+		ctx.gossiper.ProcessRemoteAnnouncement(&update, nodePeer1)
+	}()
+
+	// We know that both are being processed once the count for
+	// FindBaseByAlias has increased by 2.
+	err = wait.NoError(func() error {
+		count := findBaseByAliasCount.Load()
+
+		if count != 4 {
+			return fmt.Errorf("expected 4 calls to "+
+				"FindBaseByAlias, got %v", count)
+		}
+
+		return nil
+	}, time.Second*5)
+	require.NoError(t, err)
+
+	// Now we can un-pause the thread that grabbed the mutex first.
+	close(pause)
+
+	// Only 1 call should have made it past the staleness check to the
+	// graph's UpdateEdge call.
+	err = wait.NoError(func() error {
+		count := getUpdateEdgeCount()
+		if count != 3 {
+			return fmt.Errorf("expected 3 calls to UpdateEdge, "+
+				"got %v", count)
+		}
+
+		return nil
+	}, time.Second*5)
+	require.NoError(t, err)
+
+	// We'll define a helper to assert whether update was broadcast or not.
+	assertBroadcast := func(shouldBroadcast bool) {
+		t.Helper()
+
+		select {
+		case <-ctx.broadcastedMessage:
+			require.True(t, shouldBroadcast)
+		case <-time.After(2 * trickleDelay):
+			require.False(t, shouldBroadcast)
+		}
+	}
+
+	processUpdate := func(msg lnwire.Message, peer lnpeer.Peer) {
+		select {
+		case err := <-ctx.gossiper.ProcessRemoteAnnouncement(
+			msg, peer,
+		):
+			require.NoError(t, err)
+		case <-time.After(time.Second):
+			t.Fatal("remote announcement not processed")
+		}
+	}
+
+	// Show that the last update was broadcast.
+	assertBroadcast(true)
+
+	// We should be allowed to send another update now since the rate limit
+	// has still not been met.
+	refreshUpdate()
+	processUpdate(&update, nodePeer1)
+	assertBroadcast(true)
+
+	// Our rate limit should be hit now, so a new update should not be
+	// broadcast.
+	refreshUpdate()
+	processUpdate(&update, nodePeer1)
+	assertBroadcast(false)
+}
+
 // TestRateLimitChannelUpdates ensures that we properly rate limit incoming
 // channel updates.
 func TestRateLimitChannelUpdates(t *testing.T) {

docs/release-notes/release-notes-0.19.0.md

@@ -77,6 +77,11 @@
   restarts, for details check [this
   issue](https://github.com/lightningnetwork/lnd/issues/8975#issuecomment-2270528222).
 
+* [Fix a bug](https://github.com/lightningnetwork/lnd/pull/9573) where 
+  processing duplicate ChannelUpdates from different peers in quick succession 
+  could lead to our ChannelUpdate rate limiting logic being prematurely 
+  triggered.
+
 # New Features
 
 * [Support](https://github.com/lightningnetwork/lnd/pull/8390) for