From daf6de4f14cc898bb59932e927e946fd8b9ca4bf Mon Sep 17 00:00:00 2001
From: Aleksandar Pesic <peske.nis@gmail.com>
Date: Tue, 23 Feb 2021 04:29:54 +0100
Subject: [PATCH] wgengine: make NewUserspaceEngine wait for TUN interface to
 be up on Windows

Updates #474

Signed-off-by: Aleksandar Pesic <peske.nis@gmail.com>
---
 wgengine/ifstatus_noop.go    |  19 ++++++
 wgengine/ifstatus_windows.go | 111 +++++++++++++++++++++++++++++++++++
 wgengine/userspace.go        |   4 ++
 3 files changed, 134 insertions(+)
 create mode 100644 wgengine/ifstatus_noop.go
 create mode 100644 wgengine/ifstatus_windows.go

diff --git a/wgengine/ifstatus_noop.go b/wgengine/ifstatus_noop.go
new file mode 100644
index 000000000..7564d67ec
--- /dev/null
+++ b/wgengine/ifstatus_noop.go
@@ -0,0 +1,19 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !windows
+
+package wgengine
+
+import (
+	"time"
+
+	"github.com/tailscale/wireguard-go/tun"
+	"tailscale.com/types/logger"
+)
+
+// Dummy implementation that does nothing.
+func waitInterfaceUp(iface tun.Device, timeout time.Duration, logf logger.Logf) error {
+	return nil
+}
diff --git a/wgengine/ifstatus_windows.go b/wgengine/ifstatus_windows.go
new file mode 100644
index 000000000..840b6cf39
--- /dev/null
+++ b/wgengine/ifstatus_windows.go
@@ -0,0 +1,111 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package wgengine
+
+import (
+	"fmt"
+	"sync"
+	"time"
+
+	"github.com/tailscale/wireguard-go/tun"
+	"golang.zx2c4.com/wireguard/windows/tunnel/winipcfg"
+	"tailscale.com/types/logger"
+)
+
+// ifaceWatcher waits for an interface to be up.
+type ifaceWatcher struct {
+	logf logger.Logf
+	luid winipcfg.LUID
+
+	mu   sync.Mutex // guards following
+	done bool
+	sig  chan bool
+}
+
+// callback is the callback we register with Windows to call when IP interface changes.
+func (iw *ifaceWatcher) callback(notificationType winipcfg.MibNotificationType, iface *winipcfg.MibIPInterfaceRow) {
+	// Probably should check only when MibParameterNotification, but just in case included MibAddInstance also.
+	if notificationType == winipcfg.MibParameterNotification || notificationType == winipcfg.MibAddInstance {
+		// Out of paranoia, start a goroutine to finish our work, to return to Windows out of this callback.
+		go iw.isUp()
+	}
+}
+
+func (iw *ifaceWatcher) isUp() bool {
+	iw.mu.Lock()
+	defer iw.mu.Unlock()
+
+	if iw.done {
+		// We already know that it's up
+		return true
+	}
+
+	if iw.getOperStatus() != winipcfg.IfOperStatusUp {
+		return false
+	}
+
+	iw.done = true
+	iw.sig <- true
+	return true
+}
+
+func (iw *ifaceWatcher) getOperStatus() winipcfg.IfOperStatus {
+	ifc, err := iw.luid.Interface()
+	if err != nil {
+		iw.logf("iw.luid.Interface error: %v", err)
+		return 0
+	}
+	return ifc.OperStatus
+}
+
+func waitInterfaceUp(iface tun.Device, timeout time.Duration, logf logger.Logf) error {
+	iw := &ifaceWatcher{
+		luid: winipcfg.LUID(iface.(*tun.NativeTun).LUID()),
+		logf: logger.WithPrefix(logf, "waitInterfaceUp: "),
+	}
+
+	// Just in case check the status first
+	if iw.getOperStatus() == winipcfg.IfOperStatusUp {
+		iw.logf("TUN interface already up; no need to wait")
+		return nil
+	}
+
+	iw.sig = make(chan bool, 1)
+	cb, err := winipcfg.RegisterInterfaceChangeCallback(iw.callback)
+	if err != nil {
+		iw.logf("RegisterInterfaceChangeCallback error: %v", err)
+		return err
+	}
+	defer cb.Unregister()
+
+	t0 := time.Now()
+	expires := t0.Add(timeout)
+	ticker := time.NewTicker(10 * time.Second)
+	defer ticker.Stop()
+
+	for {
+		iw.logf("waiting for TUN interface to come up...")
+
+		select {
+		case <-iw.sig:
+			iw.logf("TUN interface is up after %v", time.Since(t0))
+			return nil
+		case <-ticker.C:
+			break
+		}
+
+		if iw.isUp() {
+			// Very unlikely to happen - either NotifyIpInterfaceChange doesn't work
+			// or it came up in the same moment as tick. Indicate this in the log message.
+			iw.logf("TUN interface is up after %v (on poll, without notification)", time.Since(t0))
+			return nil
+		}
+
+		if expires.Before(time.Now()) {
+			iw.logf("timeout waiting %v for TUN interface to come up", timeout)
+			return fmt.Errorf("timeout waiting for TUN interface to come up")
+		}
+	}
+}
diff --git a/wgengine/userspace.go b/wgengine/userspace.go
index bcb4025c7..952abfc09 100644
--- a/wgengine/userspace.go
+++ b/wgengine/userspace.go
@@ -187,6 +187,10 @@ func NewUserspaceEngine(logf logger.Logf, tunName string, listenPort uint16) (En
 	}
 	logf("CreateTUN ok.")
 
+	if err := waitInterfaceUp(tun, 90*time.Second, logf); err != nil {
+		return nil, err
+	}
+
 	conf := EngineConfig{
 		Logf:       logf,
 		TUN:        tun,