From 46dbf5404013e83867356ea8a590a45a569acbf4 Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Thu, 2 May 2019 23:53:15 +0200
Subject: [PATCH] wintun: don't retry when not creating

The only time we're trying to counteract the race condition is when
we're creating a driver. When we're simply looking up all drivers, it
doesn't make sense to retry.
---
 tun/wintun/registryhacks_windows.go |  6 +++---
 tun/wintun/wintun_windows.go        | 29 +++++++++++++++++++++++------
 2 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/tun/wintun/registryhacks_windows.go b/tun/wintun/registryhacks_windows.go
index bbcc020..94cc2f3 100644
--- a/tun/wintun/registryhacks_windows.go
+++ b/tun/wintun/registryhacks_windows.go
@@ -11,7 +11,7 @@ import (
 )
 
 const (
-	numRetries = 100
+	numRetries   = 100
 	retryTimeout = 150 * time.Millisecond
 )
 
@@ -21,7 +21,7 @@ func registryOpenKeyRetry(k registry.Key, path string, access uint32) (key regis
 		if err == nil {
 			break
 		}
-		if i != numRetries - 1 {
+		if i != numRetries-1 {
 			time.Sleep(retryTimeout)
 		}
 	}
@@ -34,7 +34,7 @@ func keyGetStringValueRetry(k registry.Key, name string) (val string, valtype ui
 		if err == nil {
 			break
 		}
-		if i != numRetries - 1 {
+		if i != numRetries-1 {
 			time.Sleep(retryTimeout)
 		}
 	}
diff --git a/tun/wintun/wintun_windows.go b/tun/wintun/wintun_windows.go
index eae283b..e1b46a8 100644
--- a/tun/wintun/wintun_windows.go
+++ b/tun/wintun/wintun_windows.go
@@ -38,7 +38,7 @@ const machineName = ""
 //
 // MakeWintun creates interface handle and populates it from device registry key
 //
-func MakeWintun(deviceInfoSet setupapi.DevInfo, deviceInfoData *setupapi.DevInfoData) (*Wintun, error) {
+func makeWintun(deviceInfoSet setupapi.DevInfo, deviceInfoData *setupapi.DevInfoData, wait bool) (*Wintun, error) {
 	// Open HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\<class>\<id> registry key.
 	key, err := deviceInfoSet.OpenDevRegKey(deviceInfoData, setupapi.DICS_FLAG_GLOBAL, 0, setupapi.DIREG_DRV, registry.READ)
 	if err != nil {
@@ -50,7 +50,11 @@ func MakeWintun(deviceInfoSet setupapi.DevInfo, deviceInfoData *setupapi.DevInfo
 	var valueType uint32
 
 	// Read the NetCfgInstanceId value.
-	valueStr, valueType, err = keyGetStringValueRetry(key, "NetCfgInstanceId")
+	if wait {
+		valueStr, valueType, err = keyGetStringValueRetry(key, "NetCfgInstanceId")
+	} else {
+		valueStr, valueType, err = key.GetStringValue("NetCfgInstanceId")
+	}
 	if err != nil {
 		return nil, errors.New("RegQueryStringValue(\"NetCfgInstanceId\") failed: " + err.Error())
 	}
@@ -121,13 +125,14 @@ func GetInterface(ifname string, hwndParent uintptr) (*Wintun, error) {
 		}
 
 		// Get interface ID.
-		wintun, err := MakeWintun(devInfoList, deviceData)
+		wintun, err := makeWintun(devInfoList, deviceData, false)
 		if err != nil {
 			continue
 		}
 
+		//TODO: is there a better way than comparing ifnames?
 		// Get interface name.
-		ifname2, err := wintun.GetInterfaceName()
+		ifname2, err := wintun.getInterfaceNameNoRetry()
 		if err != nil {
 			continue
 		}
@@ -301,7 +306,7 @@ func CreateInterface(description string, hwndParent uintptr) (*Wintun, bool, err
 		// installation continues in the background. It might take a while, before all registry
 		// keys and values are populated.
 		for numAttempts := 0; numAttempts < 30; numAttempts++ {
-			wintun, err = MakeWintun(devInfoList, deviceData)
+			wintun, err = makeWintun(devInfoList, deviceData, true)
 			if err != nil {
 				if errWin, ok := err.(syscall.Errno); ok && errWin == windows.ERROR_FILE_NOT_FOUND {
 					// Wait and retry. TODO: Wait for a cancellable event instead.
@@ -371,7 +376,8 @@ func (wintun *Wintun) DeleteInterface(hwndParent uintptr) (bool, bool, error) {
 		}
 
 		// Get interface ID.
-		wintun2, err := MakeWintun(devInfoList, deviceData)
+		//TODO: Store some ID in the Wintun object such that this call isn't required.
+		wintun2, err := makeWintun(devInfoList, deviceData, false)
 		if err != nil {
 			continue
 		}
@@ -446,6 +452,17 @@ func (wintun *Wintun) GetInterfaceName() (string, error) {
 	return getRegStringValue(key, "Name")
 }
 
+func (wintun *Wintun) getInterfaceNameNoRetry() (string, error) {
+	key, err := registry.OpenKey(registry.LOCAL_MACHINE, wintun.GetNetRegKeyName(), registry.QUERY_VALUE)
+	if err != nil {
+		return "", errors.New("Network-specific registry key open failed: " + err.Error())
+	}
+	defer key.Close()
+
+	// Get the interface name.
+	return getRegStringValue(key, "Name")
+}
+
 //
 // SetInterfaceName sets network interface name.
 //