From d87cbeeb2fb152b5f377758c68c655e09fe177f3 Mon Sep 17 00:00:00 2001
From: Simon Rozman <simon@rozman.si>
Date: Thu, 7 Feb 2019 22:02:51 +0100
Subject: wintun: Detect if a foreign interface with the same name exists

Signed-off-by: Simon Rozman <simon@rozman.si>
---
 tun/tun_windows.go           | 16 +++++++++++++---
 tun/wintun/wintun_windows.go | 39 ++++++++++++++++++++++++++++++++++++---
 2 files changed, 49 insertions(+), 6 deletions(-)

diff --git a/tun/tun_windows.go b/tun/tun_windows.go
index 5f4f22a..5c231e7 100644
--- a/tun/tun_windows.go
+++ b/tun/tun_windows.go
@@ -55,16 +55,26 @@ type nativeTun struct {
 func CreateTUN(ifname string) (TUNDevice, error) {
 	// Does an interface with this name already exist?
 	wt, err := wintun.GetInterface(ifname, 0)
-	if wt == nil || err != nil {
+	if wt == nil {
 		// Interface does not exist or an error occured. Create one.
 		wt, _, err = wintun.CreateInterface("WireGuard Tunnel Adapter", 0)
 		if err != nil {
 			return nil, err
 		}
+	} else if err != nil {
+		// Foreign interface with the same name found.
+		// We could create a Wintun interface under a temporary name. But, should our
+		// proces die without deleting this interface first, the interface would remain
+		// orphaned.
+		return nil, err
+	}
 
-		// Set interface name. (Ignore errors.)
-		wt.SetInterfaceName(ifname)
+	err = wt.SetInterfaceName(ifname)
+	if err != nil {
+		wt.DeleteInterface(0)
+		return nil, err
 	}
+
 	err = wt.FlushInterface()
 	if err != nil {
 		wt.DeleteInterface(0)
diff --git a/tun/wintun/wintun_windows.go b/tun/wintun/wintun_windows.go
index 75180d5..f9fc309 100644
--- a/tun/wintun/wintun_windows.go
+++ b/tun/wintun/wintun_windows.go
@@ -35,7 +35,8 @@ const TUN_HWID = "Wintun"
 // hwndParent to 0.
 //
 // Function returns interface ID when the interface was found, or nil
-// otherwise.
+// otherwise. If the interface is found but not Wintun-class, the function
+// returns interface ID with an error.
 //
 func GetInterface(ifname string, hwndParent uintptr) (*Wintun, error) {
 	// Create a list of network devices.
@@ -79,8 +80,40 @@ func GetInterface(ifname string, hwndParent uintptr) (*Wintun, error) {
 		}
 
 		if ifname == strings.ToLower(ifname2) {
-			// Interface name found.
-			return (*Wintun)(ifid), nil
+			// Interface name found. Check its driver.
+			const driverType = setupapi.SPDIT_COMPATDRIVER
+			err = devInfoList.BuildDriverInfoList(deviceData, driverType)
+			if err != nil {
+				return nil, err
+			}
+			defer devInfoList.DestroyDriverInfoList(deviceData, driverType)
+
+			for index := 0; ; index++ {
+				// Get a driver from the list.
+				driverData, err := devInfoList.EnumDriverInfo(deviceData, driverType, index)
+				if err != nil {
+					if errWin, ok := err.(syscall.Errno); ok && errWin == 259 /*ERROR_NO_MORE_ITEMS*/ {
+						break
+					}
+					// Something is wrong with this driver. Skip it.
+					continue
+				}
+
+				// Get driver info details.
+				driverDetailData, err := devInfoList.GetDriverInfoDetail(deviceData, driverData)
+				if err != nil {
+					// Something is wrong with this driver. Skip it.
+					continue
+				}
+
+				if driverDetailData.IsCompatible(TUN_HWID) {
+					// Matching hardware ID found.
+					return (*Wintun)(ifid), nil
+				}
+			}
+
+			// This interface is not using Wintun driver.
+			return (*Wintun)(ifid), errors.New("Foreign network interface with the same name exists")
 		}
 	}
 
-- 
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