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tailscale/net/netns/netns_windows.go

113 lines
3.2 KiB
Go

// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package netns
import (
"encoding/binary"
"syscall"
"unsafe"
"github.com/tailscale/winipcfg-go"
"golang.org/x/sys/windows"
"tailscale.com/net/interfaces"
)
func interfaceIndex(iface *winipcfg.Interface) uint32 {
if iface == nil {
// The zero ifidx means "unspecified". If we end up passing zero
// to bindSocket*(), it unsets the binding and lets the socket
// behave as normal again, which is what we want if there's no
// default route we can use.
return 0
}
return iface.Index
}
// control binds c to the Windows interface that holds a default
// route, and is not the Tailscale WinTun interface.
func control(network, address string, c syscall.RawConn) error {
canV4, canV6 := false, false
switch network {
case "tcp", "udp":
canV4, canV6 = true, true
case "tcp4", "udp4":
canV4 = true
case "tcp6", "udp6":
canV6 = true
}
if canV4 {
iface, err := interfaces.GetWindowsDefault(winipcfg.AF_INET)
if err != nil {
return err
}
if err := bindSocket4(c, interfaceIndex(iface)); err != nil {
return err
}
}
if canV6 {
iface, err := interfaces.GetWindowsDefault(winipcfg.AF_INET6)
if err != nil {
return err
}
if err := bindSocket6(c, interfaceIndex(iface)); err != nil {
return err
}
}
return nil
}
// sockoptBoundInterface is the value of IP_UNICAST_IF and IPV6_UNICAST_IF.
//
// See https://docs.microsoft.com/en-us/windows/win32/winsock/ipproto-ip-socket-options
// and https://docs.microsoft.com/en-us/windows/win32/winsock/ipproto-ipv6-socket-options
const sockoptBoundInterface = 31
// bindSocket4 binds the given RawConn to the network interface with
// index ifidx, for IPv4 traffic only.
func bindSocket4(c syscall.RawConn, ifidx uint32) error {
// For IPv4 (but NOT IPv6) the interface index must be passed
// as a big-endian integer (regardless of platform endianness)
// because the underlying sockopt takes either an IPv4 address
// or an index shoved into IPv4 address representation (an IP
// in 0.0.0.0/8 means it's actually an index).
//
// See https://docs.microsoft.com/en-us/windows/win32/winsock/ipproto-ip-socket-options
// and IP_UNICAST_IF.
indexAsAddr := nativeToBigEndian(ifidx)
var controlErr error
err := c.Control(func(fd uintptr) {
controlErr = windows.SetsockoptInt(windows.Handle(fd), windows.IPPROTO_IP, sockoptBoundInterface, int(indexAsAddr))
})
if err != nil {
return err
}
return controlErr
}
// bindSocket6 binds the given RawConn to the network interface with
// index ifidx, for IPv6 traffic only.
func bindSocket6(c syscall.RawConn, ifidx uint32) error {
var controlErr error
err := c.Control(func(fd uintptr) {
controlErr = windows.SetsockoptInt(windows.Handle(fd), windows.IPPROTO_IPV6, sockoptBoundInterface, int(ifidx))
})
if err != nil {
return err
}
return controlErr
}
// nativeToBigEndian returns i converted into big-endian
// representation, suitable for passing to Windows APIs that require a
// mangled uint32.
func nativeToBigEndian(i uint32) uint32 {
var b [4]byte
binary.BigEndian.PutUint32(b[:], i)
return *(*uint32)(unsafe.Pointer(&b[0]))
}