From 4aa52d267f000f84caf912c62fc14a5b8e7cacb5 Mon Sep 17 00:00:00 2001
From: "Johan T. Halseth" <johanth@gmail.com>
Date: Sat, 12 Jan 2019 18:59:45 +0100
Subject: [PATCH] funding+lnwallet: ensure max_htlc_value_in_flight smaller
 than capacity

Return an error to the remote if larger.
---
 fundingmanager.go          |  6 ++++--
 lnwallet/errors.go         | 10 ++++++++++
 lnwallet/interface_test.go | 16 ++++++++++++----
 lnwallet/reservation.go    | 14 ++++++++++++--
 4 files changed, 38 insertions(+), 8 deletions(-)

diff --git a/fundingmanager.go b/fundingmanager.go
index f2591206..5d18a828 100644
--- a/fundingmanager.go
+++ b/fundingmanager.go
@@ -1090,7 +1090,7 @@ func (f *fundingManager) handleFundingOpen(fmsg *fundingOpenMsg) {
 		MaxAcceptedHtlcs: msg.MaxAcceptedHTLCs,
 		CsvDelay:         msg.CsvDelay,
 	}
-	err = reservation.CommitConstraints(channelConstraints)
+	err = reservation.CommitConstraints(channelConstraints, amt)
 	if err != nil {
 		fndgLog.Errorf("Unacceptable channel constraints: %v", err)
 		f.failFundingFlow(fmsg.peer, fmsg.msg.PendingChannelID, err)
@@ -1254,7 +1254,9 @@ func (f *fundingManager) handleFundingAccept(fmsg *fundingAcceptMsg) {
 		MaxAcceptedHtlcs: msg.MaxAcceptedHTLCs,
 		CsvDelay:         msg.CsvDelay,
 	}
-	err = resCtx.reservation.CommitConstraints(channelConstraints)
+	err = resCtx.reservation.CommitConstraints(
+		channelConstraints, resCtx.chanAmt,
+	)
 	if err != nil {
 		fndgLog.Warnf("Unacceptable channel constraints: %v", err)
 		f.failFundingFlow(fmsg.peer, fmsg.msg.PendingChannelID, err)
diff --git a/lnwallet/errors.go b/lnwallet/errors.go
index 79ab10f7..d72caf65 100644
--- a/lnwallet/errors.go
+++ b/lnwallet/errors.go
@@ -132,6 +132,16 @@ func ErrNumConfsTooLarge(numConfs, maxNumConfs uint32) error {
 	}
 }
 
+// ErrMaxValueInFlightTooLarge returns an error indicating that the 'max HTLC
+// value in flight' the remote required is too large to be accepted.
+func ErrMaxValueInFlightTooLarge(maxValInFlight,
+	maxMaxValInFlight lnwire.MilliSatoshi) ReservationError {
+	return ReservationError{
+		fmt.Errorf("maxValueInFlight too large: %v, max is %v",
+			maxValInFlight, maxMaxValInFlight),
+	}
+}
+
 // ErrChanTooSmall returns an error indicating that an incoming channel request
 // was too small. We'll reject any incoming channels if they're below our
 // configured value for the min channel size we'll accept.
diff --git a/lnwallet/interface_test.go b/lnwallet/interface_test.go
index 4549a266..7ed0dfe9 100644
--- a/lnwallet/interface_test.go
+++ b/lnwallet/interface_test.go
@@ -437,7 +437,9 @@ func testDualFundingReservationWorkflow(miner *rpctest.Harness,
 		MaxAcceptedHtlcs: lnwallet.MaxHTLCNumber / 2,
 		CsvDelay:         csvDelay,
 	}
-	err = aliceChanReservation.CommitConstraints(channelConstraints)
+	err = aliceChanReservation.CommitConstraints(
+		channelConstraints, fundingAmount*2,
+	)
 	if err != nil {
 		t.Fatalf("unable to verify constraints: %v", err)
 	}
@@ -471,7 +473,9 @@ func testDualFundingReservationWorkflow(miner *rpctest.Harness,
 	if err != nil {
 		t.Fatalf("bob unable to init channel reservation: %v", err)
 	}
-	err = bobChanReservation.CommitConstraints(channelConstraints)
+	err = bobChanReservation.CommitConstraints(
+		channelConstraints, fundingAmount*2,
+	)
 	if err != nil {
 		t.Fatalf("unable to verify constraints: %v", err)
 	}
@@ -869,7 +873,9 @@ func testSingleFunderReservationWorkflow(miner *rpctest.Harness,
 		MaxAcceptedHtlcs: lnwallet.MaxHTLCNumber / 2,
 		CsvDelay:         csvDelay,
 	}
-	err = aliceChanReservation.CommitConstraints(channelConstraints)
+	err = aliceChanReservation.CommitConstraints(
+		channelConstraints, fundingAmt,
+	)
 	if err != nil {
 		t.Fatalf("unable to verify constraints: %v", err)
 	}
@@ -903,7 +909,9 @@ func testSingleFunderReservationWorkflow(miner *rpctest.Harness,
 	if err != nil {
 		t.Fatalf("unable to create bob reservation: %v", err)
 	}
-	err = bobChanReservation.CommitConstraints(channelConstraints)
+	err = bobChanReservation.CommitConstraints(
+		channelConstraints, fundingAmt,
+	)
 	if err != nil {
 		t.Fatalf("unable to verify constraints: %v", err)
 	}
diff --git a/lnwallet/reservation.go b/lnwallet/reservation.go
index a32acfa2..1a684f25 100644
--- a/lnwallet/reservation.go
+++ b/lnwallet/reservation.go
@@ -286,7 +286,9 @@ func (r *ChannelReservation) SetNumConfsRequired(numConfs uint16) {
 // of satoshis that can be transferred in a single commitment. This function
 // will also attempt to verify the constraints for sanity, returning an error
 // if the parameters are seemed unsound.
-func (r *ChannelReservation) CommitConstraints(c *channeldb.ChannelConstraints) error {
+func (r *ChannelReservation) CommitConstraints(c *channeldb.ChannelConstraints,
+	capacity btcutil.Amount) error {
+
 	r.Lock()
 	defer r.Unlock()
 
@@ -341,7 +343,15 @@ func (r *ChannelReservation) CommitConstraints(c *channeldb.ChannelConstraints)
 		)
 	}
 
-	// Our dust limit should always be less than or equal to our proposed
+	// Fail if the maxValueInFlight is greater than the channel capacity.
+	capacityMsat := lnwire.NewMSatFromSatoshis(capacity)
+	if c.MaxPendingAmount > capacityMsat {
+		return ErrMaxValueInFlightTooLarge(
+			c.MaxPendingAmount, capacityMsat,
+		)
+	}
+
+	// Our dust limit should always be less than or equal our proposed
 	// channel reserve.
 	if r.ourContribution.DustLimit > c.ChanReserve {
 		r.ourContribution.DustLimit = c.ChanReserve