Update

vendor/tailscale.com/ipn/ipnlocal/peerapi_linux.go

@@ -0,0 +1,50 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build linux && !android
+
+package ipnlocal
+
+import (
+	"net"
+	"net/netip"
+
+	"tailscale.com/net/netns"
+)
+
+func init() {
+	initListenConfig = initListenConfigTun
+}
+
+// initListenConfigTun binds the peerapi listener to the tunnel interface
+// with SO_BINDTODEVICE.
+//
+// Linux delivers a packet addressed to the node's own Tailscale IP via
+// INPUT from any interface it arrives on (weak host model), so a
+// LAN-adjacent attacker could otherwise complete a TCP handshake with
+// the kernel-level listener, confirming that this machine's MAC
+// address belongs to a given tailnet identity (the peerapi port is
+// derived from the Tailscale IP). Binding the listener to the tunnel
+// interface drops those handshakes at socket lookup. macOS and iOS
+// already bind this listener to the tunnel interface with IP_BOUND_IF,
+// and Windows is protected by its strong host model.
+//
+// No legitimate traffic is lost. Connections to the node's Tailscale
+// IP from the local host are delivered via the tunnel interface, peer
+// connections arrive that way in builds without userspace netstack,
+// and with netstack compiled in (the usual case) peer connections are
+// terminated in userspace and never reach the kernel listener at all.
+// In netstack mode there is no tunnel interface and the listener binds
+// all addresses; the only connections that reach it are loopback dials
+// from netstack and from the local host, so loopback is the right
+// device there.
+func initListenConfigTun(config *net.ListenConfig, addr netip.Addr, tunIfIndex int) error {
+	device := "lo"
+	if tunIfIndex != 0 {
+		iface, err := net.InterfaceByIndex(tunIfIndex)
+		if err == nil {
+			device = iface.Name
+		}
+	}
+	return netns.SetListenConfigInterfaceName(config, device)
+}