[PATCH] Respect WG protocol reserved bytes

[Laura Zelenku <laura.zelenku@wandera.com>]

Packet that respects WG protocol contains Type on first byte followed by
three reserved bytes. Because wireguard-go implementation uses element
pools it is required to make sure that reserved bytes are cleared for
outgoing traffic (can get dirty by "bad" clients). Clearing reserved
bytes is also for backwards compatibility.

Signed-off-by: Laura Zelenku <laura.zelenku@wandera.com>
---
 device/noise-protocol.go | 12 ++++++++----
 device/receive.go        |  4 ++--
 device/send.go           |  6 ++++--
 3 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/device/noise-protocol.go b/device/noise-protocol.go
index 0212b7d..b5ef72b 100644
--- a/device/noise-protocol.go
+++ b/device/noise-protocol.go
@@ -82,7 +82,8 @@ const (
  */
 
 type MessageInitiation struct {
-       Type      uint32
+       Type      uint8
+       Reserved  [3]byte
        Sender    uint32
        Ephemeral NoisePublicKey
        Static    [NoisePublicKeySize + poly1305.TagSize]byte
@@ -92,7 +93,8 @@ type MessageInitiation struct {
 }
 
 type MessageResponse struct {
-       Type      uint32
+       Type      uint8
+       Reserved  [3]byte
        Sender    uint32
        Receiver  uint32
        Ephemeral NoisePublicKey
@@ -102,14 +104,16 @@ type MessageResponse struct {
 }
 
 type MessageTransport struct {
-       Type     uint32
+       Type     uint8
+       Reserved [3]byte
        Receiver uint32
        Counter  uint64
        Content  []byte
 }
 
 type MessageCookieReply struct {
-       Type     uint32
+       Type     uint8
+       Reserved [3]byte
        Receiver uint32
        Nonce    [chacha20poly1305.NonceSizeX]byte
        Cookie   [blake2s.Size128 + poly1305.TagSize]byte
diff --git a/device/receive.go b/device/receive.go
index b1959c6..e0d57bc 100644
--- a/device/receive.go
+++ b/device/receive.go
@@ -22,7 +22,7 @@ import (
 )
 
 type QueueHandshakeElement struct {
-       msgType  uint32
+       msgType  uint8
        packet   []byte
        endpoint conn.Endpoint
        buffer   *[MaxMessageSize]byte
@@ -121,7 +121,7 @@ func (device *Device) RoutineReceiveIncoming(IP int, bind conn.Bind) {
                // check size of packet
 
                packet := buffer[:size]
-               msgType := binary.LittleEndian.Uint32(packet[:4])
+               msgType := packet[0]
 
                var okay bool
 
diff --git a/device/send.go b/device/send.go
index a437cf1..dc4a8e2 100644
--- a/device/send.go
+++ b/device/send.go
@@ -373,11 +373,13 @@ func (device *Device) RoutineEncryption() {
                // populate header fields
                header := elem.buffer[:MessageTransportHeaderSize]
 
-               fieldType := header[0:4]
+               fieldType := header[0:1]
+               fieldReserved := header[1:4]
                fieldReceiver := header[4:8]
                fieldNonce := header[8:16]
 
-               binary.LittleEndian.PutUint32(fieldType, MessageTransportType)
+               fieldType[0] = byte(MessageTransportType)
+               copy(fieldReserved, []byte{}) // clear reserved bytes
                binary.LittleEndian.PutUint32(fieldReceiver, elem.keypair.remoteIndex)
                binary.LittleEndian.PutUint64(fieldNonce, elem.nonce)
 
-- 
2.28.0



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