From 9d7e9b956232ed67dc5266f12e224beebc31356f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E4=B8=96=E7=95=8C?= <i@sekai.icu>
Date: Wed, 22 Jul 2026 14:49:44 +0800
Subject: [PATCH] Fix Tailscale 4via6 subnet routing

---
 protocol/tailscale/endpoint.go | 43 +++++++++++++++++++++-------------
 1 file changed, 27 insertions(+), 16 deletions(-)

diff --git a/protocol/tailscale/endpoint.go b/protocol/tailscale/endpoint.go
index a248260f..34f6a277 100644
--- a/protocol/tailscale/endpoint.go
+++ b/protocol/tailscale/endpoint.go
@@ -706,12 +706,17 @@ func (t *Endpoint) NewConnectionEx(ctx context.Context, conn net.Conn, source M.
 	metadata.Inbound = t.Tag()
 	metadata.InboundType = t.Type()
 	metadata.Source = source
-	addr4, addr6 := t.server.TailscaleIPs()
-	switch destination.Addr {
-	case addr4:
-		destination.Addr = netip.AddrFrom4([4]uint8{127, 0, 0, 1})
-	case addr6:
-		destination.Addr = netip.IPv6Loopback()
+	destinationAddress := tsaddr.UnmapVia(destination.Addr)
+	if destinationAddress != destination.Addr {
+		destination.Addr = destinationAddress
+	} else {
+		addr4, addr6 := t.server.TailscaleIPs()
+		switch destination.Addr {
+		case addr4:
+			destination.Addr = netip.AddrFrom4([4]uint8{127, 0, 0, 1})
+		case addr6:
+			destination.Addr = netip.IPv6Loopback()
+		}
 	}
 	metadata.Destination = destination
 	t.logger.InfoContext(ctx, "inbound connection from ", source)
@@ -724,16 +729,22 @@ func (t *Endpoint) NewPacketConnectionEx(ctx context.Context, conn N.PacketConn,
 	metadata.Inbound = t.Tag()
 	metadata.InboundType = t.Type()
 	metadata.Source = source
-	addr4, addr6 := t.server.TailscaleIPs()
-	switch destination.Addr {
-	case addr4:
-		metadata.OriginDestination = destination
-		destination.Addr = netip.AddrFrom4([4]uint8{127, 0, 0, 1})
-		conn = bufio.NewNATPacketConn(bufio.NewNetPacketConn(conn), metadata.OriginDestination, destination)
-	case addr6:
-		metadata.OriginDestination = destination
-		destination.Addr = netip.IPv6Loopback()
-		conn = bufio.NewNATPacketConn(bufio.NewNetPacketConn(conn), metadata.OriginDestination, destination)
+	originDestination := destination
+	destinationAddress := tsaddr.UnmapVia(destination.Addr)
+	if destinationAddress != destination.Addr {
+		destination.Addr = destinationAddress
+	} else {
+		addr4, addr6 := t.server.TailscaleIPs()
+		switch destination.Addr {
+		case addr4:
+			destination.Addr = netip.AddrFrom4([4]uint8{127, 0, 0, 1})
+		case addr6:
+			destination.Addr = netip.IPv6Loopback()
+		}
+	}
+	if destination != originDestination {
+		metadata.OriginDestination = originDestination
+		conn = bufio.NewNATPacketConn(bufio.NewNetPacketConn(conn), originDestination, destination)
 	}
 	metadata.Destination = destination
 	t.logger.InfoContext(ctx, "inbound packet connection from ", source)