WireGuard proxy: Fix potential startup races (#6852)

https://github.com/XTLS/Xray-core/pull/6852#issuecomment-5871816550

Fixes https://github.com/XTLS/Xray-core/issues/6850

proxy/wireguard/bind.go

@@ -52,9 +52,12 @@ func (b *bind) Open(port uint16) (fns []conn.ReceiveFunc, actualPort uint16, err
 						case <-ch:
 						default:
 							errors.LogErrorInner(context.Background(), err, "unexpected closed")
-							if b.downFunc != nil {
+							b.mu.Lock()
+							downFunc := b.downFunc
+							b.mu.Unlock()
+							if downFunc != nil {
 								go func() {
-									common.Must(b.downFunc())
+									common.Must(downFunc())
 								}()
 							}
 						}
@@ -76,6 +79,13 @@ func (b *bind) Open(port uint16) (fns []conn.ReceiveFunc, actualPort uint16, err
 	}, uint16(c.LocalAddr().(*net.UDPAddr).Port), nil
 }
 
+// setDownFunc sets downFunc after the device is created, since the device may already be using the bind.
+func (b *bind) setDownFunc(f func() error) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	b.downFunc = f
+}
+
 func (b *bind) Close() error {
 	b.mu.Lock()
 	defer b.mu.Unlock()