wintun: rename device using undocumented API that netsh.exe uses

tun/wintun/netshell/netshell_windows.go

@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: MIT
+ *
+ * Copyright (C) 2019 WireGuard LLC. All Rights Reserved.
+ */
+
+package netshell
+
+import (
+	"syscall"
+	"unsafe"
+
+	"golang.org/x/sys/windows"
+)
+
+var (
+	modnetshell = windows.NewLazySystemDLL("netshell.dll")
+	procHrRenameConnection = modnetshell.NewProc("HrRenameConnection")
+)
+
+func HrRenameConnection(guid *windows.GUID, newName *uint16) (err error) {
+	err = procHrRenameConnection.Find()
+	if err != nil {
+		// Missing from servercore, so we can't presume it's always there.
+		return
+	}
+
+	ret, _, _ := syscall.Syscall(procHrRenameConnection.Addr(), 2, uintptr(unsafe.Pointer(guid)), uintptr(unsafe.Pointer(newName)), 0)
+	if ret != 0 {
+		err = syscall.Errno(ret)
+	}
+	return
+}

tun/wintun/wintun_windows.go

@@ -8,6 +8,7 @@ package wintun
 import (
 	"errors"
 	"fmt"
+	"golang.zx2c4.com/wireguard/tun/wintun/netshell"
 	"strings"
 	"syscall"
 	"time"
@@ -449,13 +450,20 @@ func (wintun *Wintun) GetInterfaceName() (string, error) {
 // SetInterfaceName sets network interface name.
 //
 func (wintun *Wintun) SetInterfaceName(ifname string) error {
+	// We open the registry key before calling HrRename, because the registry open will wait until the key exists.
 	key, err := registryOpenKeyRetry(registry.LOCAL_MACHINE, wintun.GetNetRegKeyName(), registry.SET_VALUE)
 	if err != nil {
 		return errors.New("Network-specific registry key open failed: " + err.Error())
 	}
 	defer key.Close()
 
-	// Set the interface name.
+	// We have to tell the various runtime COM services about the new name too. We ignore the
+	// error because netshell isn't available on servercore.
+	// TODO: netsh.exe falls back to NciSetConnection in this case. If somebody complains, maybe
+	// we should do the same.
+	_ = netshell.HrRenameConnection(&wintun.CfgInstanceID, windows.StringToUTF16Ptr(ifname))
+
+	// Set the interface name. The above line should have done this too, but in case it failed, we force it.
 	return key.SetStringValue("Name", ifname)
 }