From e924280baa36f6fd80f4a65f2fb6223a4965b281 Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Sun, 9 Jun 2019 19:20:17 +0200
Subject: [PATCH] wintun: allow controlling GUID

---
 tun/tun_windows.go           | 10 +++++++++-
 tun/wintun/wintun_windows.go | 21 ++++++++++++++++++++-
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/tun/tun_windows.go b/tun/tun_windows.go
index 0b41be9..1881e5b 100644
--- a/tun/tun_windows.go
+++ b/tun/tun_windows.go
@@ -60,6 +60,14 @@ func packetAlign(size uint32) uint32 {
 // adapter with the same name exist, it is reused.
 //
 func CreateTUN(ifname string) (TUNDevice, error) {
+	return CreateTUNWithRequestedGUID(ifname, nil)
+}
+
+//
+// CreateTUNWithRequestedGUID creates a Wintun adapter with the given name and
+// a requested GUID. Should a Wintun adapter with the same name exist, it is reused.
+//
+func CreateTUNWithRequestedGUID(ifname string, requestedGUID *windows.GUID) (TUNDevice, error) {
 	var err error
 	var wt *wintun.Wintun
 
@@ -74,7 +82,7 @@ func CreateTUN(ifname string) (TUNDevice, error) {
 	} else if err == windows.ERROR_ALREADY_EXISTS {
 		return nil, fmt.Errorf("Foreign network interface with the same name exists")
 	}
-	wt, _, err = wintun.CreateInterface("WireGuard Tunnel Adapter", 0)
+	wt, _, err = wintun.CreateInterface("WireGuard Tunnel Adapter", requestedGUID, 0)
 	if err != nil {
 		return nil, fmt.Errorf("Unable to create Wintun interface: %v", err)
 	}
diff --git a/tun/wintun/wintun_windows.go b/tun/wintun/wintun_windows.go
index ec7f8ea..9e71581 100644
--- a/tun/wintun/wintun_windows.go
+++ b/tun/wintun/wintun_windows.go
@@ -176,6 +176,13 @@ func GetInterface(ifname string, hwndParent uintptr) (*Wintun, error) {
 // description is a string that supplies the text description of the device.
 // description is optional and can be "".
 //
+// requestedGUID is the GUID of the created network interface, which then
+// influences NLA generation deterministically. If it is set to nil, the GUID
+// is chosen by the system at random, and hence a new NLA entry is created for
+// each new interface. It is called "requested" GUID because the API it uses
+// is completely undocumented, and so there could be minor interesting
+// complications with its usage.
+//
 // hwndParent is a handle to the top-level window to use for any user
 // interface that is related to non-device-specific actions (such as a select-
 // device dialog box that uses the global class driver list). This handle is
@@ -184,7 +191,7 @@ func GetInterface(ifname string, hwndParent uintptr) (*Wintun, error) {
 //
 // Function returns the network interface ID and a flag if reboot is required.
 //
-func CreateInterface(description string, hwndParent uintptr) (*Wintun, bool, error) {
+func CreateInterface(description string, requestedGUID *windows.GUID, hwndParent uintptr) (*Wintun, bool, error) {
 	// Create an empty device info set for network adapter device class.
 	devInfoList, err := setupapi.SetupDiCreateDeviceInfoListEx(&deviceClassNetGUID, hwndParent, machineName)
 	if err != nil {
@@ -280,6 +287,18 @@ func CreateInterface(description string, hwndParent uintptr) (*Wintun, bool, err
 	// Register device co-installers if any. (Ignore errors)
 	devInfoList.CallClassInstaller(setupapi.DIF_REGISTER_COINSTALLERS, deviceData)
 
+	if requestedGUID != nil {
+		key, err := devInfoList.OpenDevRegKey(deviceData, setupapi.DICS_FLAG_GLOBAL, 0, setupapi.DIREG_DRV, registry.SET_VALUE)
+		if err != nil {
+			return nil, false, fmt.Errorf("OpenDevRegKey failed: %v", err)
+		}
+		err = key.SetStringValue("NetSetupAnticipatedInstanceId", requestedGUID.String())
+		key.Close()
+		if err != nil {
+			return nil, false, fmt.Errorf("SetStringValue(NetSetupAnticipatedInstanceId) failed: %v", err)
+		}
+	}
+
 	// Install interfaces if any. (Ignore errors)
 	devInfoList.CallClassInstaller(setupapi.DIF_INSTALLINTERFACES, deviceData)