From 59fea192b7859607d44c8703f31eabfd118a9ec4 Mon Sep 17 00:00:00 2001
From: eugene <elzeigel@gmail.com>
Date: Mon, 4 Apr 2022 16:33:51 -0400
Subject: [PATCH] server+routing: pass isAlias to router

This allows the router to determine what is and isn't an alias from
lnd's definition of an alias. Any ChannelAnnouncement that has an
alias ShortChannelID field is not verified on-chain. To prevent a
DoS vector from existing, the gossiper ensures that only the local
lnd node can send its ChannelAnnouncements to the router with an
alias ShortChannelID.
---
 routing/payment_lifecycle_test.go |  3 +++
 routing/router.go                 | 12 ++++++++++--
 routing/router_test.go            | 26 ++++++++++++++++++++++++++
 server.go                         |  1 +
 4 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/routing/payment_lifecycle_test.go b/routing/payment_lifecycle_test.go
index 81c88ee3b..b34c63eb6 100644
--- a/routing/payment_lifecycle_test.go
+++ b/routing/payment_lifecycle_test.go
@@ -473,6 +473,9 @@ func testPaymentLifecycle(t *testing.T, test paymentLifecycleTestCase,
 				return next, nil
 			},
 			Clock: clock.NewTestClock(time.Unix(1, 0)),
+			IsAlias: func(scid lnwire.ShortChannelID) bool {
+				return false
+			},
 		})
 		if err != nil {
 			t.Fatalf("unable to create router %v", err)
diff --git a/routing/router.go b/routing/router.go
index 71e72c3d1..9e97291e0 100644
--- a/routing/router.go
+++ b/routing/router.go
@@ -358,6 +358,10 @@ type Config struct {
 	// Otherwise, we'll only prune the channel when both edges have a very
 	// dated last update.
 	StrictZombiePruning bool
+
+	// IsAlias returns whether a passed ShortChannelID is an alias. This is
+	// only used for our local channels.
+	IsAlias func(scid lnwire.ShortChannelID) bool
 }
 
 // EdgeLocator is a struct used to identify a specific edge.
@@ -1455,8 +1459,12 @@ func (r *ChannelRouter) processUpdate(msg interface{},
 		// If AssumeChannelValid is present, then we are unable to
 		// perform any of the expensive checks below, so we'll
 		// short-circuit our path straight to adding the edge to our
-		// graph.
-		if r.cfg.AssumeChannelValid {
+		// graph. If the passed ShortChannelID is an alias, then we'll
+		// skip validation as it will not map to a legitimate tx. This
+		// is not a DoS vector as only we can add an alias
+		// ChannelAnnouncement from the gossiper.
+		scid := lnwire.NewShortChanIDFromInt(msg.ChannelID)
+		if r.cfg.AssumeChannelValid || r.cfg.IsAlias(scid) {
 			if err := r.cfg.Graph.AddChannelEdge(msg, op...); err != nil {
 				return fmt.Errorf("unable to add edge: %v", err)
 			}
diff --git a/routing/router_test.go b/routing/router_test.go
index 4ffee7be7..a5425a3db 100644
--- a/routing/router_test.go
+++ b/routing/router_test.go
@@ -82,6 +82,9 @@ func (c *testCtx) RestartRouter(t *testing.T) {
 		Control:            makeMockControlTower(),
 		ChannelPruneExpiry: time.Hour * 24,
 		GraphPruneInterval: time.Hour * 2,
+		IsAlias: func(scid lnwire.ShortChannelID) bool {
+			return false
+		},
 	})
 	require.NoError(t, err, "unable to create router")
 	require.NoError(t, router.Start(), "unable to start router")
@@ -165,6 +168,9 @@ func createTestCtxFromGraphInstanceAssumeValid(t *testing.T,
 		Clock:               clock.NewTestClock(time.Unix(1, 0)),
 		AssumeChannelValid:  assumeValid,
 		StrictZombiePruning: strictPruning,
+		IsAlias: func(scid lnwire.ShortChannelID) bool {
+			return false
+		},
 	})
 	require.NoError(t, err, "unable to create router")
 	require.NoError(t, router.Start(), "unable to start router")
@@ -1738,6 +1744,10 @@ func TestWakeUpOnStaleBranch(t *testing.T) {
 
 		// We'll set the delay to zero to prune immediately.
 		FirstTimePruneDelay: 0,
+
+		IsAlias: func(scid lnwire.ShortChannelID) bool {
+			return false
+		},
 	})
 	if err != nil {
 		t.Fatalf("unable to create router %v", err)
@@ -3485,6 +3495,10 @@ func TestSendMPPaymentSucceed(t *testing.T) {
 			next := atomic.AddUint64(&uniquePaymentID, 1)
 			return next, nil
 		},
+
+		IsAlias: func(scid lnwire.ShortChannelID) bool {
+			return false
+		},
 	})
 	require.NoError(t, err, "failed to create router")
 
@@ -3648,6 +3662,10 @@ func TestSendMPPaymentSucceedOnExtraShards(t *testing.T) {
 			next := atomic.AddUint64(&uniquePaymentID, 1)
 			return next, nil
 		},
+
+		IsAlias: func(scid lnwire.ShortChannelID) bool {
+			return false
+		},
 	})
 	require.NoError(t, err, "failed to create router")
 
@@ -3856,6 +3874,10 @@ func TestSendMPPaymentFailed(t *testing.T) {
 			next := atomic.AddUint64(&uniquePaymentID, 1)
 			return next, nil
 		},
+
+		IsAlias: func(scid lnwire.ShortChannelID) bool {
+			return false
+		},
 	})
 	require.NoError(t, err, "failed to create router")
 
@@ -4056,6 +4078,10 @@ func TestSendMPPaymentFailedWithShardsInFlight(t *testing.T) {
 			next := atomic.AddUint64(&uniquePaymentID, 1)
 			return next, nil
 		},
+
+		IsAlias: func(scid lnwire.ShortChannelID) bool {
+			return false
+		},
 	})
 	require.NoError(t, err, "failed to create router")
 
diff --git a/server.go b/server.go
index da69c02b0..0f79612b9 100644
--- a/server.go
+++ b/server.go
@@ -920,6 +920,7 @@ func newServer(cfg *Config, listenAddrs []net.Addr,
 		PathFindingConfig:   pathFindingConfig,
 		Clock:               clock.NewDefaultClock(),
 		StrictZombiePruning: strictPruning,
+		IsAlias:             aliasmgr.IsAlias,
 	})
 	if err != nil {
 		return nil, fmt.Errorf("can't create router: %v", err)