Fix unmarshal of packets with padding

WebRTC clients use padding only packets as probe
packets for bandwidth estimation. As padding was
not removed from the payload, downstream code
trying to parse padding as valid media payload
results in erroneous parsing

Testing:
--------
- Add unit tests for different padding scenarios
- Check that ion-sfu does not try to parse padding only
packets as valid video payload.

AUTHORS.txt

@@ -8,7 +8,9 @@ aler9 <46489434+aler9@users.noreply.github.com>
 Antoine Baché <antoine.bache@epitech.eu>
 Antoine Baché <antoine@tenten.app>
 Atsushi Watanabe <atsushi.w@ieee.org>
+baiyufei <baiyufei@outlook.com>
 Bao Nguyen <bao@n4n.dev>
+boks1971 <raja.gobi@tutanota.com>
 debiandebiandebian <debiandebiandebiandebian@gmail.com>
 ffmiyo <leffmiyo@gmail.com>
 Guilherme <gqgs@protonmail.com>

packet.go

@@ -214,8 +214,17 @@ func (p *Packet) Unmarshal(rawPacket []byte) error {
 		return err
 	}
 
-	p.Payload = rawPacket[p.PayloadOffset:]
+	end := len(rawPacket)
+	if p.Header.Padding {
+		end -= int(rawPacket[end-1])
+	}
+	if end < p.PayloadOffset {
+		return errTooSmall
+	}
+
+	p.Payload = rawPacket[p.PayloadOffset:end]
 	p.Raw = rawPacket
+
 	return nil
 }
 

packet_test.go

@@ -22,6 +22,7 @@ func TestBasic(t *testing.T) {
 	}
 	parsedPacket := &Packet{
 		Header: Header{
+			Padding:          false,
 			Marker:           true,
 			Extension:        true,
 			ExtensionProfile: 1,
@@ -73,6 +74,108 @@ func TestBasic(t *testing.T) {
 			}
 		})
 	}
+
+	// packet with padding
+	rawPkt = []byte{
+		0xb0, 0xe0, 0x69, 0x8f, 0xd9, 0xc2, 0x93, 0xda, 0x1c, 0x64,
+		0x27, 0x82, 0x00, 0x01, 0x00, 0x01, 0xFF, 0xFF, 0xFF, 0xFF, 0x98, 0x36, 0xbe, 0x88, 0x04,
+	}
+	parsedPacket = &Packet{
+		Header: Header{
+			Padding:          true,
+			Marker:           true,
+			Extension:        true,
+			ExtensionProfile: 1,
+			Extensions: []Extension{
+				{0, []byte{
+					0xFF, 0xFF, 0xFF, 0xFF,
+				}},
+			},
+			Version:        2,
+			PayloadType:    96,
+			SequenceNumber: 27023,
+			Timestamp:      3653407706,
+			SSRC:           476325762,
+			CSRC:           []uint32{},
+			PayloadOffset:  20,
+		},
+		Payload: rawPkt[20:21],
+		Raw:     rawPkt,
+	}
+	if err := p.Unmarshal(rawPkt); err != nil {
+		t.Error(err)
+	} else if !reflect.DeepEqual(p, parsedPacket) {
+		t.Errorf("TestBasic padding unmarshal: got %#v, want %#v", p, parsedPacket)
+	}
+
+	// packet with only padding
+	rawPkt = []byte{
+		0xb0, 0xe0, 0x69, 0x8f, 0xd9, 0xc2, 0x93, 0xda, 0x1c, 0x64,
+		0x27, 0x82, 0x00, 0x01, 0x00, 0x01, 0xFF, 0xFF, 0xFF, 0xFF, 0x98, 0x36, 0xbe, 0x88, 0x05,
+	}
+	parsedPacket = &Packet{
+		Header: Header{
+			Padding:          true,
+			Marker:           true,
+			Extension:        true,
+			ExtensionProfile: 1,
+			Extensions: []Extension{
+				{0, []byte{
+					0xFF, 0xFF, 0xFF, 0xFF,
+				}},
+			},
+			Version:        2,
+			PayloadType:    96,
+			SequenceNumber: 27023,
+			Timestamp:      3653407706,
+			SSRC:           476325762,
+			CSRC:           []uint32{},
+			PayloadOffset:  20,
+		},
+		Payload: []byte{},
+		Raw:     rawPkt,
+	}
+	if err := p.Unmarshal(rawPkt); err != nil {
+		t.Error(err)
+	} else if !reflect.DeepEqual(p, parsedPacket) {
+		t.Errorf("TestBasic padding only unmarshal: got %#v, want %#v", p, parsedPacket)
+	}
+	if len(p.Payload) != 0 {
+		t.Errorf("Unmarshal of padding only packet has payload of non-zero length: %d", len(p.Payload))
+	}
+
+	// packet with excessive padding
+	rawPkt = []byte{
+		0xb0, 0xe0, 0x69, 0x8f, 0xd9, 0xc2, 0x93, 0xda, 0x1c, 0x64,
+		0x27, 0x82, 0x00, 0x01, 0x00, 0x01, 0xFF, 0xFF, 0xFF, 0xFF, 0x98, 0x36, 0xbe, 0x88, 0x06,
+	}
+	parsedPacket = &Packet{
+		Header: Header{
+			Padding:          true,
+			Marker:           true,
+			Extension:        true,
+			ExtensionProfile: 1,
+			Extensions: []Extension{
+				{0, []byte{
+					0xFF, 0xFF, 0xFF, 0xFF,
+				}},
+			},
+			Version:        2,
+			PayloadType:    96,
+			SequenceNumber: 27023,
+			Timestamp:      3653407706,
+			SSRC:           476325762,
+			CSRC:           []uint32{},
+		},
+		Payload: []byte{},
+	}
+	err := p.Unmarshal(rawPkt)
+	if err == nil {
+		t.Fatal("Unmarshal did not error on packet with excessive padding")
+	}
+	if !errors.Is(err, errTooSmall) {
+		t.Errorf("Expected error: %v, got: %v", errTooSmall, err)
+	}
 }
 
 func TestExtension(t *testing.T) {