From 57b69e3b1ab18017a4f42ce5c42635ce162f811f Mon Sep 17 00:00:00 2001
From: Wilmer Paulino <wilmer.paulino@gmail.com>
Date: Fri, 17 Jan 2020 11:51:09 -0800
Subject: [PATCH] discovery: check ChainHash in QueryChannelRange messages

If the provided ChainHash in a QueryChannelRange message does not match
that of our current chain, then we should send a blank response, rather
than reply with channels for the wrong chain.
---
 discovery/syncer.go      | 17 +++++++++++++
 discovery/syncer_test.go | 55 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+)

diff --git a/discovery/syncer.go b/discovery/syncer.go
index 8348abc5..a154f990 100644
--- a/discovery/syncer.go
+++ b/discovery/syncer.go
@@ -894,6 +894,23 @@ func (g *GossipSyncer) replyPeerQueries(msg lnwire.Message) error {
 // ensure that our final fragment carries the "complete" bit to indicate the
 // end of our streaming response.
 func (g *GossipSyncer) replyChanRangeQuery(query *lnwire.QueryChannelRange) error {
+	// Before responding, we'll check to ensure that the remote peer is
+	// querying for the same chain that we're on. If not, we'll send back a
+	// response with a complete value of zero to indicate we're on a
+	// different chain.
+	if g.cfg.chainHash != query.ChainHash {
+		log.Warnf("Remote peer requested QueryChannelRange for "+
+			"chain=%v, we're on chain=%v", query.ChainHash,
+			g.cfg.chainHash)
+
+		return g.cfg.sendToPeerSync(&lnwire.ReplyChannelRange{
+			QueryChannelRange: *query,
+			Complete:          0,
+			EncodingType:      g.cfg.encodingType,
+			ShortChanIDs:      nil,
+		})
+	}
+
 	log.Infof("GossipSyncer(%x): filtering chan range: start_height=%v, "+
 		"num_blocks=%v", g.cfg.peerPub[:], query.FirstBlockHeight,
 		query.NumBlocks)
diff --git a/discovery/syncer_test.go b/discovery/syncer_test.go
index 1b1f8890..606fc062 100644
--- a/discovery/syncer_test.go
+++ b/discovery/syncer_test.go
@@ -533,6 +533,61 @@ func TestGossipSyncerApplyGossipFilter(t *testing.T) {
 	}
 }
 
+// TestGossipSyncerQueryChannelRangeWrongChainHash tests that if we receive a
+// channel range query for the wrong chain, then we send back a response with no
+// channels and complete=0.
+func TestGossipSyncerQueryChannelRangeWrongChainHash(t *testing.T) {
+	t.Parallel()
+
+	// First, we'll create a GossipSyncer instance with a canned sendToPeer
+	// message to allow us to intercept their potential sends.
+	msgChan, syncer, _ := newTestSyncer(
+		lnwire.NewShortChanIDFromInt(10), defaultEncoding,
+		defaultChunkSize,
+	)
+
+	// We'll now ask the syncer to reply to a channel range query, but for a
+	// chain that it isn't aware of.
+	query := &lnwire.QueryChannelRange{
+		ChainHash:        *chaincfg.SimNetParams.GenesisHash,
+		FirstBlockHeight: 0,
+		NumBlocks:        math.MaxUint32,
+	}
+	err := syncer.replyChanRangeQuery(query)
+	if err != nil {
+		t.Fatalf("unable to process short chan ID's: %v", err)
+	}
+
+	select {
+	case <-time.After(time.Second * 15):
+		t.Fatalf("no msgs received")
+
+	case msgs := <-msgChan:
+		// We should get back exactly one message, that's a
+		// ReplyChannelRange with a matching query, and a complete value
+		// of zero.
+		if len(msgs) != 1 {
+			t.Fatalf("wrong messages: expected %v, got %v",
+				1, len(msgs))
+		}
+
+		msg, ok := msgs[0].(*lnwire.ReplyChannelRange)
+		if !ok {
+			t.Fatalf("expected lnwire.ReplyChannelRange, got %T", msg)
+		}
+
+		if msg.QueryChannelRange != *query {
+			t.Fatalf("wrong query channel range in reply: "+
+				"expected: %v\ngot: %v", spew.Sdump(*query),
+				spew.Sdump(msg.QueryChannelRange))
+		}
+		if msg.Complete != 0 {
+			t.Fatalf("expected complete set to 0, got %v",
+				msg.Complete)
+		}
+	}
+}
+
 // TestGossipSyncerReplyShortChanIDsWrongChainHash tests that if we get a chan
 // ID query for the wrong chain, then we send back only a short ID end with
 // complete=0.