WireGuard proxy: Prevent panic when closing netTun with a write in flight (#6778)

https://github.com/XTLS/Xray-core/pull/6778#pullrequestreview-5251957308

proxy/wireguard/netstack.go

@@ -44,6 +44,7 @@ type netTun struct {
 	events         chan tun.Event
 	notifyHandle   *channel.NotificationHandle
 	incomingPacket chan *buffer.View
+	closed         chan struct{}
 	mtu            int
 	dnsServers     []netip.Addr
 	hasV4, hasV6   bool
@@ -60,6 +61,7 @@ func CreateNetTUN(localAddresses, dnsServers []netip.Addr, mtu int, handleLocal
 		stack:          stack.New(opts),
 		events:         make(chan tun.Event, 10),
 		incomingPacket: make(chan *buffer.View),
+		closed:         make(chan struct{}),
 		dnsServers:     dnsServers,
 		mtu:            mtu,
 	}
@@ -126,8 +128,10 @@ func (tun *netTun) Events() <-chan tun.Event {
 }
 
 func (tun *netTun) Read(buf [][]byte, sizes []int, offset int) (int, error) {
-	view, ok := <-tun.incomingPacket
-	if !ok {
+	var view *buffer.View
+	select {
+	case view = <-tun.incomingPacket:
+	case <-tun.closed:
 		return 0, os.ErrClosed
 	}
 
@@ -168,7 +172,10 @@ func (tun *netTun) WriteNotify() {
 	view := pkt.ToView()
 	pkt.DecRef()
 
-	tun.incomingPacket <- view
+	select {
+	case tun.incomingPacket <- view:
+	case <-tun.closed:
+	}
 }
 
 func (tun *netTun) Close() error {
@@ -181,8 +188,9 @@ func (tun *netTun) Close() error {
 		close(tun.events)
 	}
 
-	if tun.incomingPacket != nil {
-		close(tun.incomingPacket)
+	// we don't close incomingPacket, because WriteNotify may be mid-send on it (DNS lookup) and would panic.
+	if tun.closed != nil {
+		close(tun.closed)
 	}
 
 	return nil