htlcswitch: support fat error generation and relay

Author: joostjager

feature/default_sets.go

@@ -83,4 +83,9 @@ var defaultSetDesc = setDesc{
 		SetInit:    {}, // I
 		SetNodeAnn: {}, // N
 	},
+	lnwire.AttributableErrorsOptional: {
+		SetInit:    {}, // I
+		SetNodeAnn: {}, // N
+		SetInvoice: {}, // 9
+	},
 }

htlcswitch/circuit_test.go

@@ -34,6 +34,10 @@ var (
 	// testExtracter is a precomputed extraction of testEphemeralKey, using
 	// the sphinxPrivKey.
 	testExtracter *hop.SphinxErrorEncrypter
+
+	// testAttributableExtracter is a precomputed extraction of
+	// testEphemeralKey, using the sphinxPrivKey.
+	testAttributableExtracter *hop.SphinxErrorEncrypter
 )
 
 func init() {
@@ -74,12 +78,17 @@ func initTestExtracter() {
 	}
 
 	testExtracter = hop.NewSphinxErrorEncrypter(
-		testEphemeralKey, sharedSecret,
+		testEphemeralKey, sharedSecret, false,
+	)
+
+	testAttributableExtracter = hop.NewSphinxErrorEncrypter(
+		testEphemeralKey, sharedSecret, true,
 	)
 
 	// We also set this error extracter on startup, otherwise it will be nil
 	// at compile-time.
 	halfCircuitTests[2].encrypter = testExtracter
+	halfCircuitTests[3].encrypter = testAttributableExtracter
 }
 
 // newOnionProcessor creates starts a new htlcswitch.OnionProcessor using a temp
@@ -175,6 +184,14 @@ var halfCircuitTests = []struct {
 		// repopulate this encrypter.
 		encrypter: testExtracter,
 	},
+	{
+		hash:      hash3,
+		inValue:   10000,
+		outValue:  9000,
+		chanID:    lnwire.NewShortChanIDFromInt(3),
+		htlcID:    3,
+		encrypter: testAttributableExtracter,
+	},
 }
 
 // TestHalfCircuitSerialization checks that the half circuits can be properly

htlcswitch/hop/error_encryptor.go

@@ -2,14 +2,36 @@ package hop
 
 import (
 	"bytes"
+	"encoding/binary"
+	"errors"
 	"fmt"
 	"io"
+	"time"
 
 	"github.com/btcsuite/btcd/btcec/v2"
 	sphinx "github.com/lightningnetwork/lightning-onion"
 	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/lightningnetwork/lnd/tlv"
 )
 
+const (
+	// A set of tlv type definitions used to serialize the encrypter to the
+	// database.
+	//
+	// NOTE: A migration should be added whenever this list changes. This
+	// prevents against the database being rolled back to an older
+	// format where the surrounding logic might assume a different set of
+	// fields are known.
+	creationTimeType tlv.Type = 0
+)
+
+// AttrErrorStruct defines the message structure for an attributable error. Use
+// a maximum route length of 20, a fixed payload length of 4 bytes to
+// accommodate the a 32-bit hold time in milliseconds and use 4 byte hmacs.
+// Total size including a 256 byte message from the error source works out to
+// 1200 bytes.
+var AttrErrorStruct = sphinx.NewAttrErrorStructure(20, 4, 4)
+
 // EncrypterType establishes an enum used in serialization to indicate how to
 // decode a concrete instance of the ErrorEncrypter interface.
 type EncrypterType byte
@@ -27,6 +49,8 @@ const (
 	EncrypterTypeMock = 2
 )
 
+var byteOrder = binary.BigEndian
+
 // SharedSecretGenerator defines a function signature that extracts a shared
 // secret from an sphinx OnionPacket.
 type SharedSecretGenerator func(*btcec.PublicKey) (sphinx.Hash256,
@@ -80,9 +104,12 @@ type ErrorEncrypter interface {
 // result, all errors handled are themselves wrapped in layers of onion
 // encryption and must be treated as such accordingly.
 type SphinxErrorEncrypter struct {
-	*sphinx.OnionErrorEncrypter
+	encrypter interface{}
 
 	EphemeralKey *btcec.PublicKey
+	CreatedAt    time.Time
+
+	attrError bool
 }
 
 // NewSphinxErrorEncrypterUninitialized initializes a blank sphinx error
@@ -94,8 +121,7 @@ type SphinxErrorEncrypter struct {
 //     OnionProcessor.
 func NewSphinxErrorEncrypterUninitialized() *SphinxErrorEncrypter {
 	return &SphinxErrorEncrypter{
-		OnionErrorEncrypter: nil,
-		EphemeralKey:        &btcec.PublicKey{},
+		EphemeralKey: &btcec.PublicKey{},
 	}
 }
 
@@ -104,10 +130,18 @@ func NewSphinxErrorEncrypterUninitialized() *SphinxErrorEncrypter {
 // SphinxErrorEncrypter, use the NewSphinxErrorEncrypterUninitialized
 // constructor.
 func NewSphinxErrorEncrypter(ephemeralKey *btcec.PublicKey,
-	sharedSecret sphinx.Hash256) *SphinxErrorEncrypter {
+	sharedSecret sphinx.Hash256,
+	attrError bool) *SphinxErrorEncrypter {
 
 	encrypter := &SphinxErrorEncrypter{
 		EphemeralKey: ephemeralKey,
+		attrError:    attrError,
+	}
+
+	if attrError {
+		// Set creation time rounded to nanosecond to avoid differences
+		// after serialization.
+		encrypter.CreatedAt = time.Now().Truncate(time.Nanosecond)
 	}
 
 	encrypter.initialize(sharedSecret)
@@ -116,9 +150,40 @@ func NewSphinxErrorEncrypter(ephemeralKey *btcec.PublicKey,
 }
 
 func (s *SphinxErrorEncrypter) initialize(sharedSecret sphinx.Hash256) {
-	s.OnionErrorEncrypter = sphinx.NewOnionErrorEncrypter(
-		sharedSecret,
-	)
+	if s.attrError {
+		s.encrypter = sphinx.NewOnionAttrErrorEncrypter(
+			sharedSecret, AttrErrorStruct,
+		)
+	} else {
+		s.encrypter = sphinx.NewOnionErrorEncrypter(
+			sharedSecret,
+		)
+	}
+}
+
+func (s *SphinxErrorEncrypter) getHoldTimeMs() uint32 {
+	return uint32(time.Since(s.CreatedAt).Milliseconds())
+}
+
+func (s *SphinxErrorEncrypter) encrypt(initial bool,
+	data []byte) (lnwire.OpaqueReason, error) {
+
+	switch encrypter := s.encrypter.(type) {
+	case *sphinx.OnionErrorEncrypter:
+		return encrypter.EncryptError(initial, data), nil
+
+	case *sphinx.OnionAttrErrorEncrypter:
+		// Pass hold time as the payload.
+		holdTimeMs := s.getHoldTimeMs()
+
+		var payload [4]byte
+		byteOrder.PutUint32(payload[:], holdTimeMs)
+
+		return encrypter.EncryptError(initial, data, payload[:])
+
+	default:
+		panic("unexpected encrypter type")
+	}
 }
 
 // EncryptFirstHop transforms a concrete failure message into an encrypted
@@ -135,9 +200,7 @@ func (s *SphinxErrorEncrypter) EncryptFirstHop(
 		return nil, err
 	}
 
-	// We pass a true as the first parameter to indicate that a MAC should
-	// be added.
-	return s.EncryptError(true, b.Bytes()), nil
+	return s.encrypt(true, b.Bytes())
 }
 
 // EncryptMalformedError is similar to EncryptFirstHop (it adds the MAC), but
@@ -150,7 +213,7 @@ func (s *SphinxErrorEncrypter) EncryptFirstHop(
 func (s *SphinxErrorEncrypter) EncryptMalformedError(
 	reason lnwire.OpaqueReason) (lnwire.OpaqueReason, error) {
 
-	return s.EncryptError(true, reason), nil
+	return s.encrypt(true, reason)
 }
 
 // IntermediateEncrypt wraps an already encrypted opaque reason error in an
@@ -163,7 +226,24 @@ func (s *SphinxErrorEncrypter) EncryptMalformedError(
 func (s *SphinxErrorEncrypter) IntermediateEncrypt(
 	reason lnwire.OpaqueReason) (lnwire.OpaqueReason, error) {
 
-	return s.EncryptError(false, reason), nil
+	encrypted, err := s.encrypt(false, reason)
+	switch {
+	// If the structure of the error received from downstream is invalid,
+	// then generate a new failure message with a valid structure so that
+	// the sender is able to penalize the offending node.
+	case errors.Is(err, sphinx.ErrInvalidStructure):
+		// Use an all-zeroes failure message. This is not a defined
+		// message, but the sender will at least know where the error
+		// occurred.
+		reason = make([]byte, lnwire.FailureMessageLength+2+2)
+
+		return s.encrypt(true, reason)
+
+	case err != nil:
+		return lnwire.OpaqueReason{}, err
+	}
+
+	return encrypted, nil
 }
 
 // Type returns the identifier for a sphinx error encrypter.
@@ -176,7 +256,25 @@ func (s *SphinxErrorEncrypter) Type() EncrypterType {
 func (s *SphinxErrorEncrypter) Encode(w io.Writer) error {
 	ephemeral := s.EphemeralKey.SerializeCompressed()
 	_, err := w.Write(ephemeral)
-	return err
+	if err != nil {
+		return err
+	}
+
+	// Stop here for legacy errors.
+	if !s.attrError {
+		return nil
+	}
+
+	var creationTime = uint64(s.CreatedAt.UnixNano())
+
+	tlvStream, err := tlv.NewStream(
+		tlv.MakePrimitiveRecord(creationTimeType, &creationTime),
+	)
+	if err != nil {
+		return err
+	}
+
+	return tlvStream.Encode(w)
 }
 
 // Decode reconstructs the error encrypter's ephemeral public key from the
@@ -193,6 +291,30 @@ func (s *SphinxErrorEncrypter) Decode(r io.Reader) error {
 		return err
 	}
 
+	// Try decode attributable error structure.
+	var creationTime uint64
+
+	tlvStream, err := tlv.NewStream(
+		tlv.MakePrimitiveRecord(creationTimeType, &creationTime),
+	)
+	if err != nil {
+		return err
+	}
+
+	typeMap, err := tlvStream.DecodeWithParsedTypes(r)
+	if err != nil {
+		return err
+	}
+
+	// Return early if this encrypter is not for attributable errors.
+	if len(typeMap) == 0 {
+		return nil
+	}
+
+	// Set attributable error flag and creation time.
+	s.attrError = true
+	s.CreatedAt = time.Unix(0, int64(creationTime))
+
 	return nil
 }
 

htlcswitch/hop/payload.go

@@ -97,6 +97,10 @@ type Payload struct {
 	// metadata is additional data that is sent along with the payment to
 	// the payee.
 	metadata []byte
+
+	// AttributableError signals that the sender wants to receive
+	// attributable errors.
+	AttributableError bool
 }
 
 // NewLegacyPayload builds a Payload from the amount, cltv, and next hop
@@ -119,12 +123,13 @@ func NewLegacyPayload(f *sphinx.HopData) *Payload {
 // should correspond to the bytes encapsulated in a TLV onion payload.
 func NewPayloadFromReader(r io.Reader) (*Payload, error) {
 	var (
-		cid      uint64
-		amt      uint64
-		cltv     uint32
-		mpp      = &record.MPP{}
-		amp      = &record.AMP{}
-		metadata []byte
+		cid               uint64
+		amt               uint64
+		cltv              uint32
+		mpp               = &record.MPP{}
+		amp               = &record.AMP{}
+		metadata          []byte
+		attributableError = &record.AttributableError{}
 	)
 
 	tlvStream, err := tlv.NewStream(
@@ -134,6 +139,7 @@ func NewPayloadFromReader(r io.Reader) (*Payload, error) {
 		mpp.Record(),
 		amp.Record(),
 		record.NewMetadataRecord(&metadata),
+		attributableError.Record(),
 	)
 	if err != nil {
 		return nil, err
@@ -182,6 +188,12 @@ func NewPayloadFromReader(r io.Reader) (*Payload, error) {
 		metadata = nil
 	}
 
+	// If no attributable error field was parsed, set the attributable error
+	// field on the resulting payload to nil.
+	if _, ok := parsedTypes[record.AttributableErrorOnionType]; !ok {
+		attributableError = nil
+	}
+
 	// Filter out the custom records.
 	customRecords := NewCustomRecords(parsedTypes)
 
@@ -192,10 +204,11 @@ func NewPayloadFromReader(r io.Reader) (*Payload, error) {
 			AmountToForward: lnwire.MilliSatoshi(amt),
 			OutgoingCTLV:    cltv,
 		},
-		MPP:           mpp,
-		AMP:           amp,
-		metadata:      metadata,
-		customRecords: customRecords,
+		MPP:               mpp,
+		AMP:               amp,
+		metadata:          metadata,
+		customRecords:     customRecords,
+		AttributableError: attributableError != nil,
 	}, nil
 }
 

htlcswitch/link.go

@@ -162,7 +162,7 @@ type ChannelLinkConfig struct {
 	// CreateErrorEncrypter instantiates an error encrypter based on the
 	// provided encryption parameters.
 	CreateErrorEncrypter func(*btcec.PublicKey,
-		sphinx.Hash256) hop.ErrorEncrypter
+		sphinx.Hash256, bool) hop.ErrorEncrypter
 
 	// FetchLastChannelUpdate retrieves the latest routing policy for a
 	// target channel. This channel will typically be the outgoing channel
@@ -3029,9 +3029,11 @@ func (l *channelLink) processRemoteAdds(fwdPkg *channeldb.FwdPkg,
 		}
 
 		// Instantiate an error encrypter based on the extracted
-		// encryption parameters.
+		// encryption parameters. Don't assume attributable errors,
+		// because first the resolution format needs to be decoded from
+		// the onion payload.
 		obfuscator := l.cfg.CreateErrorEncrypter(
-			ephemeralKey, sharedSecret,
+			ephemeralKey, sharedSecret, false,
 		)
 
 		heightNow := l.cfg.BestHeight()
@@ -3063,6 +3065,14 @@ func (l *channelLink) processRemoteAdds(fwdPkg *channeldb.FwdPkg,
 			continue
 		}
 
+		// Now that we've successfully decoded the tlv, we can upgrade
+		// to the failure message version that the sender supports.
+		if pld.AttributableError {
+			obfuscator = l.cfg.CreateErrorEncrypter(
+				ephemeralKey, sharedSecret, true,
+			)
+		}
+
 		fwdInfo := pld.ForwardingInfo()
 
 		switch fwdInfo.NextHop {