lnwire: validate that gossip messages contain valid TLV

In this commit, we check that the extra bytes appended to gossip
messages contain valid TLV streams. We do this here for:
- channel_announcement
- channel_announcement_2
- channel_update
- channel_update_2
- node_announcement

This is in preparation for the SQL version of the graph store which will
normalise TLV streams at persistence time.

docs/release-notes/release-notes-0.20.0.md

@@ -34,7 +34,8 @@
 * Graph Store SQL implementation and migration project:
   * Introduce an [abstract graph 
     store](https://github.com/lightningnetwork/lnd/pull/9791) interface. 
- 
+  * Start [validating](https://github.com/lightningnetwork/lnd/pull/9787) that 
+    byte blobs at the end of gossip messages are valid TLV streams.
 
 ## RPC Updates
 

lnwire/channel_announcement.go

@@ -70,8 +70,8 @@ var _ SizeableMessage = (*ChannelAnnouncement1)(nil)
 // io.Reader observing the specified protocol version.
 //
 // This is part of the lnwire.Message interface.
-func (a *ChannelAnnouncement1) Decode(r io.Reader, pver uint32) error {
+func (a *ChannelAnnouncement1) Decode(r io.Reader, _ uint32) error {
-	return ReadElements(r,
+	err := ReadElements(r,
 		&a.NodeSig1,
 		&a.NodeSig2,
 		&a.BitcoinSig1,
@@ -85,6 +85,11 @@ func (a *ChannelAnnouncement1) Decode(r io.Reader, pver uint32) error {
 		&a.BitcoinKey2,
 		&a.ExtraOpaqueData,
 	)
+	if err != nil {
+		return err
+	}
+
+	return a.ExtraOpaqueData.ValidateTLV()
 }
 
 // Encode serializes the target ChannelAnnouncement into the passed io.Writer

lnwire/channel_announcement_2.go

@@ -126,7 +126,7 @@ func (c *ChannelAnnouncement2) DecodeTLVRecords(r io.Reader) error {
 		c.ExtraOpaqueData = tlvRecords
 	}
 
-	return nil
+	return c.ExtraOpaqueData.ValidateTLV()
 }
 
 // Encode serializes the target AnnounceSignatures1 into the passed io.Writer

lnwire/channel_update.go

@@ -132,7 +132,7 @@ var _ SizeableMessage = (*ChannelUpdate1)(nil)
 // io.Reader observing the specified protocol version.
 //
 // This is part of the lnwire.Message interface.
-func (a *ChannelUpdate1) Decode(r io.Reader, pver uint32) error {
+func (a *ChannelUpdate1) Decode(r io.Reader, _ uint32) error {
 	err := ReadElements(r,
 		&a.Signature,
 		a.ChainHash[:],
@@ -156,7 +156,12 @@ func (a *ChannelUpdate1) Decode(r io.Reader, pver uint32) error {
 		}
 	}
 
-	return a.ExtraOpaqueData.Decode(r)
+	err = a.ExtraOpaqueData.Decode(r)
+	if err != nil {
+		return err
+	}
+
+	return a.ExtraOpaqueData.ValidateTLV()
 }
 
 // Encode serializes the target ChannelUpdate into the passed io.Writer

lnwire/channel_update_2.go

@@ -154,7 +154,7 @@ func (c *ChannelUpdate2) DecodeTLVRecords(r io.Reader) error {
 		c.ExtraOpaqueData = tlvRecords
 	}
 
-	return nil
+	return c.ExtraOpaqueData.ValidateTLV()
 }
 
 // Encode serializes the target ChannelUpdate2 into the passed io.Writer

lnwire/extra_bytes.go

@@ -63,6 +63,28 @@ func (e *ExtraOpaqueData) Decode(r io.Reader) error {
 	return nil
 }
 
+// ValidateTLV checks that the raw bytes that make up the ExtraOpaqueData
+// instance are a valid TLV stream.
+func (e *ExtraOpaqueData) ValidateTLV() error {
+	// There is nothing to validate if the ExtraOpaqueData is nil or empty.
+	if e == nil || len(*e) == 0 {
+		return nil
+	}
+
+	tlvStream, err := tlv.NewStream()
+	if err != nil {
+		return err
+	}
+
+	// Ensure that the TLV stream is valid by attempting to decode it.
+	_, err = tlvStream.DecodeWithParsedTypesP2P(bytes.NewReader(*e))
+	if err != nil {
+		return fmt.Errorf("invalid TLV stream: %w: %v", err, *e)
+	}
+
+	return nil
+}
+
 // PackRecords attempts to encode the set of tlv records into the target
 // ExtraOpaqueData instance. The records will be encoded as a raw TLV stream
 // and stored within the backing slice pointer.

lnwire/node_announcement.go

@@ -112,8 +112,8 @@ var _ SizeableMessage = (*NodeAnnouncement)(nil)
 // io.Reader observing the specified protocol version.
 //
 // This is part of the lnwire.Message interface.
-func (a *NodeAnnouncement) Decode(r io.Reader, pver uint32) error {
+func (a *NodeAnnouncement) Decode(r io.Reader, _ uint32) error {
-	return ReadElements(r,
+	err := ReadElements(r,
 		&a.Signature,
 		&a.Features,
 		&a.Timestamp,
@@ -123,6 +123,11 @@ func (a *NodeAnnouncement) Decode(r io.Reader, pver uint32) error {
 		&a.Addresses,
 		&a.ExtraOpaqueData,
 	)
+	if err != nil {
+		return err
+	}
+
+	return a.ExtraOpaqueData.ValidateTLV()
 }
 
 // Encode serializes the target NodeAnnouncement into the passed io.Writer