fix: udp loopback detector not working

component/iface/iface.go

@@ -23,7 +23,7 @@ var (
 
 var interfaces = singledo.NewSingle[map[string]*Interface](time.Second * 20)
 
-func ResolveInterface(name string) (*Interface, error) {
+func Interfaces() (map[string]*Interface, error) {
 	value, err, _ := interfaces.Do(func() (map[string]*Interface, error) {
 		ifaces, err := net.Interfaces()
 		if err != nil {
@@ -69,11 +69,15 @@ func ResolveInterface(name string) (*Interface, error) {
 
 		return r, nil
 	})
+	return value, err
+}
+
+func ResolveInterface(name string) (*Interface, error) {
+	ifaces, err := Interfaces()
 	if err != nil {
 		return nil, err
 	}
 
-	ifaces := value
 	iface, ok := ifaces[name]
 	if !ok {
 		return nil, ErrIfaceNotFound
@@ -82,6 +86,21 @@ func ResolveInterface(name string) (*Interface, error) {
 	return iface, nil
 }
 
+func IsLocalIp(ip netip.Addr) (bool, error) {
+	ifaces, err := Interfaces()
+	if err != nil {
+		return false, err
+	}
+	for _, iface := range ifaces {
+		for _, addr := range iface.Addrs {
+			if addr.Contains(ip) {
+				return true, nil
+			}
+		}
+	}
+	return false, nil
+}
+
 func FlushCache() {
 	interfaces.Reset()
 }

component/loopback/detector.go

@@ -6,6 +6,7 @@ import (
 	"net/netip"
 
 	"github.com/metacubex/mihomo/common/callback"
+	"github.com/metacubex/mihomo/component/iface"
 	C "github.com/metacubex/mihomo/constant"
 
 	"github.com/puzpuzpuz/xsync/v3"
@@ -15,13 +16,13 @@ var ErrReject = errors.New("reject loopback connection")
 
 type Detector struct {
 	connMap       *xsync.MapOf[netip.AddrPort, struct{}]
-	packetConnMap *xsync.MapOf[netip.AddrPort, struct{}]
+	packetConnMap *xsync.MapOf[uint16, struct{}]
 }
 
 func NewDetector() *Detector {
 	return &Detector{
 		connMap:       xsync.NewMapOf[netip.AddrPort, struct{}](),
-		packetConnMap: xsync.NewMapOf[netip.AddrPort, struct{}](),
+		packetConnMap: xsync.NewMapOf[uint16, struct{}](),
 	}
 }
 
@@ -49,9 +50,10 @@ func (l *Detector) NewPacketConn(conn C.PacketConn) C.PacketConn {
 	if !connAddr.IsValid() {
 		return conn
 	}
-	l.packetConnMap.Store(connAddr, struct{}{})
+	port := connAddr.Port()
+	l.packetConnMap.Store(port, struct{}{})
 	return callback.NewCloseCallbackPacketConn(conn, func() {
-		l.packetConnMap.Delete(connAddr)
+		l.packetConnMap.Delete(port)
 	})
 }
 
@@ -71,7 +73,16 @@ func (l *Detector) CheckPacketConn(metadata *C.Metadata) error {
 	if !connAddr.IsValid() {
 		return nil
 	}
-	if _, ok := l.packetConnMap.Load(connAddr); ok {
+
+	isLocalIp, err := iface.IsLocalIp(connAddr.Addr())
+	if err != nil {
+		return err
+	}
+	if !isLocalIp && !connAddr.Addr().IsLoopback() {
+		return nil
+	}
+
+	if _, ok := l.packetConnMap.Load(connAddr.Port()); ok {
 		return fmt.Errorf("%w to: %s", ErrReject, metadata.RemoteAddress())
 	}
 	return nil