htlcswitch+lnd: make max cltv expiry configurable

config.go

@@ -26,6 +26,7 @@ import (
 	"github.com/lightningnetwork/lnd/chanbackup"
 	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/discovery"
+	"github.com/lightningnetwork/lnd/htlcswitch"
 	"github.com/lightningnetwork/lnd/htlcswitch/hodl"
 	"github.com/lightningnetwork/lnd/lncfg"
 	"github.com/lightningnetwork/lnd/lnrpc/routerrpc"
@@ -312,6 +313,8 @@ type config struct {
 
 	StaggerInitialReconnect bool `long:"stagger-initial-reconnect" description:"If true, will apply a randomized staggering between 0s and 30s when reconnecting to persistent peers on startup. The first 10 reconnections will be attempted instantly, regardless of the flag's value"`
 
+	MaxOutgoingCltvExpiry uint32 `long:"max-cltv-expiry" description:"The maximum number of blocks funds could be locked up for when forwarding payments."`
+
 	net tor.Net
 
 	Routing *routing.Conf `group:"routing" namespace:"routing"`
@@ -425,6 +428,7 @@ func loadConfig() (*config, error) {
 		Watchtower: &lncfg.Watchtower{
 			TowerDir: defaultTowerDir,
 		},
+		MaxOutgoingCltvExpiry: htlcswitch.DefaultMaxOutgoingCltvExpiry,
 	}
 
 	// Pre-parse the command line options to pick up an alternative config

htlcswitch/link.go

@@ -30,16 +30,16 @@ func init() {
 }
 
 const (
-	// maxCltvExpiry is the maximum outgoing time lock that the node accepts
+	// DefaultMaxOutgoingCltvExpiry is the maximum outgoing time lock that
-	// for forwarded payments. The value is relative to the current block
+	// the node accepts for forwarded payments. The value is relative to the
-	// height. The reason to have a maximum is to prevent funds getting
+	// current block height. The reason to have a maximum is to prevent
-	// locked up unreasonably long. Otherwise, an attacker willing to lock
+	// funds getting locked up unreasonably long. Otherwise, an attacker
-	// its own funds too, could force the funds of this node to be locked up
+	// willing to lock its own funds too, could force the funds of this node
-	// for an indefinite (max int32) number of blocks.
+	// to be locked up for an indefinite (max int32) number of blocks.
 	//
 	// The value 5000 is based on the maximum number of hops (20), the
 	// default cltv delta (144) and some extra margin.
-	maxCltvExpiry = 5000
+	DefaultMaxOutgoingCltvExpiry = 5000
 
 	// DefaultMinLinkFeeUpdateTimeout represents the minimum interval in
 	// which a link should propose to update its commitment fee rate.
@@ -249,6 +249,11 @@ type ChannelLinkConfig struct {
 	// encrypting, and uploading of justice transactions to the daemon's
 	// configured set of watchtowers.
 	TowerClient TowerClient
+
+	// MaxCltvExpiry is the maximum outgoing timelock that the link should
+	// accept for a forwarded HTLC. The value is relative to the current
+	// block height.
+	MaxOutgoingCltvExpiry uint32
 }
 
 // channelLink is the service which drives a channel's commitment update
@@ -2337,10 +2342,10 @@ func (l *channelLink) htlcSatifiesPolicyOutgoing(policy ForwardingPolicy,
 	}
 
 	// Check absolute max delta.
-	if timeout > maxCltvExpiry+heightNow {
+	if timeout > l.cfg.MaxOutgoingCltvExpiry+heightNow {
 		l.errorf("outgoing htlc(%x) has a time lock too far in the "+
 			"future: got %v, but maximum is %v", payHash[:],
-			timeout-heightNow, maxCltvExpiry)
+			timeout-heightNow, l.cfg.MaxOutgoingCltvExpiry)
 
 		return &lnwire.FailExpiryTooFar{}
 	}

htlcswitch/link_test.go

@@ -1692,6 +1692,7 @@ func newSingleLinkTestHarness(chanAmt, chanReserve btcutil.Amount) (
 		BatchSize:             10000,
 		MinFeeUpdateTimeout:   30 * time.Minute,
 		MaxFeeUpdateTimeout:   40 * time.Minute,
+		MaxOutgoingCltvExpiry: DefaultMaxOutgoingCltvExpiry,
 	}
 
 	const startingHeight = 100
@@ -4240,6 +4241,7 @@ func (h *persistentLinkHarness) restartLink(
 		// Set any hodl flags requested for the new link.
 		HodlMask:              hodl.MaskFromFlags(hodlFlags...),
 		DebugHTLC:             len(hodlFlags) > 0,
+		MaxOutgoingCltvExpiry: DefaultMaxOutgoingCltvExpiry,
 	}
 
 	const startingHeight = 100
@@ -5559,6 +5561,7 @@ func TestHtlcSatisfyPolicy(t *testing.T) {
 				BaseFee:       10,
 			},
 			FetchLastChannelUpdate: fetchLastChannelUpdate,
+			MaxOutgoingCltvExpiry:  DefaultMaxOutgoingCltvExpiry,
 		},
 	}
 

htlcswitch/test_utils.go

@@ -1115,6 +1115,7 @@ func (h *hopNetwork) createChannelLink(server, peer *mockServer,
 			MaxFeeUpdateTimeout:     maxFeeUpdateTimeout,
 			OnChannelFailure:        func(lnwire.ChannelID, lnwire.ShortChannelID, LinkFailureError) {},
 			OutgoingCltvRejectDelta: 3,
+			MaxOutgoingCltvExpiry:   DefaultMaxOutgoingCltvExpiry,
 		},
 		channel,
 	)

peer.go

@@ -585,6 +585,7 @@ func (p *peer) addLink(chanPoint *wire.OutPoint,
 		MaxFeeUpdateTimeout:     htlcswitch.DefaultMaxLinkFeeUpdateTimeout,
 		OutgoingCltvRejectDelta: p.outgoingCltvRejectDelta,
 		TowerClient:             p.server.towerClient,
+		MaxOutgoingCltvExpiry:   cfg.MaxOutgoingCltvExpiry,
 	}
 
 	link := htlcswitch.NewChannelLink(linkCfg, lnChan)