wireguard-go/tun/tun_linux.go

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/* SPDX-License-Identifier: MIT
*
* Copyright (C) 2017-2021 WireGuard LLC. All Rights Reserved.
*/
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package tun
/* Implementation of the TUN device interface for linux
*/
import (
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"bytes"
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"fmt"
"os"
"sync"
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"syscall"
"time"
"unsafe"
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"golang.org/x/net/ipv6"
"golang.org/x/sys/unix"
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"golang.zx2c4.com/wireguard/rwcancel"
)
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const (
cloneDevicePath = "/dev/net/tun"
ifReqSize = unix.IFNAMSIZ + 64
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)
type NativeTun struct {
tunFile *os.File
index int32 // if index
errors chan error // async error handling
events chan Event // device related events
nopi bool // the device was passed IFF_NO_PI
netlinkSock int
netlinkCancel *rwcancel.RWCancel
hackListenerClosed sync.Mutex
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statusListenersShutdown chan struct{}
closeOnce sync.Once
nameOnce sync.Once // guards calling initNameCache, which sets following fields
nameCache string // name of interface
nameErr error
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}
func (tun *NativeTun) File() *os.File {
return tun.tunFile
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}
func (tun *NativeTun) routineHackListener() {
defer tun.hackListenerClosed.Unlock()
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/* This is needed for the detection to work across network namespaces
* If you are reading this and know a better method, please get in touch.
*/
last := 0
const (
up = 1
down = 2
)
for {
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sysconn, err := tun.tunFile.SyscallConn()
if err != nil {
return
}
err2 := sysconn.Control(func(fd uintptr) {
_, err = unix.Write(int(fd), nil)
})
if err2 != nil {
return
}
switch err {
case unix.EINVAL:
if last != up {
// If the tunnel is up, it reports that write() is
// allowed but we provided invalid data.
tun.events <- EventUp
last = up
}
case unix.EIO:
if last != down {
// If the tunnel is down, it reports that no I/O
// is possible, without checking our provided data.
tun.events <- EventDown
last = down
}
default:
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return
}
select {
case <-time.After(time.Second):
// nothing
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case <-tun.statusListenersShutdown:
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return
}
}
}
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func createNetlinkSocket() (int, error) {
sock, err := unix.Socket(unix.AF_NETLINK, unix.SOCK_RAW, unix.NETLINK_ROUTE)
if err != nil {
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return -1, err
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}
saddr := &unix.SockaddrNetlink{
Family: unix.AF_NETLINK,
Groups: unix.RTMGRP_LINK | unix.RTMGRP_IPV4_IFADDR | unix.RTMGRP_IPV6_IFADDR,
}
err = unix.Bind(sock, saddr)
if err != nil {
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return -1, err
}
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return sock, nil
}
func (tun *NativeTun) routineNetlinkListener() {
defer func() {
unix.Close(tun.netlinkSock)
tun.hackListenerClosed.Lock()
close(tun.events)
tun.netlinkCancel.Close()
}()
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for msg := make([]byte, 1<<16); ; {
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var err error
var msgn int
for {
msgn, _, _, _, err = unix.Recvmsg(tun.netlinkSock, msg[:], nil, 0)
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if err == nil || !rwcancel.RetryAfterError(err) {
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break
}
if !tun.netlinkCancel.ReadyRead() {
tun.errors <- fmt.Errorf("netlink socket closed: %w", err)
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return
}
}
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if err != nil {
tun.errors <- fmt.Errorf("failed to receive netlink message: %w", err)
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return
}
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select {
case <-tun.statusListenersShutdown:
return
default:
}
wasEverUp := false
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for remain := msg[:msgn]; len(remain) >= unix.SizeofNlMsghdr; {
hdr := *(*unix.NlMsghdr)(unsafe.Pointer(&remain[0]))
if int(hdr.Len) > len(remain) {
break
}
switch hdr.Type {
case unix.NLMSG_DONE:
remain = []byte{}
case unix.RTM_NEWLINK:
info := *(*unix.IfInfomsg)(unsafe.Pointer(&remain[unix.SizeofNlMsghdr]))
remain = remain[hdr.Len:]
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if info.Index != tun.index {
// not our interface
continue
}
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if info.Flags&unix.IFF_RUNNING != 0 {
tun.events <- EventUp
wasEverUp = true
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}
if info.Flags&unix.IFF_RUNNING == 0 {
// Don't emit EventDown before we've ever emitted EventUp.
// This avoids a startup race with HackListener, which
// might detect Up before we have finished reporting Down.
if wasEverUp {
tun.events <- EventDown
}
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}
tun.events <- EventMTUUpdate
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default:
remain = remain[hdr.Len:]
}
}
}
}
func getIFIndex(name string) (int32, error) {
fd, err := unix.Socket(
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unix.AF_INET,
unix.SOCK_DGRAM,
0,
)
if err != nil {
return 0, err
}
defer unix.Close(fd)
var ifr [ifReqSize]byte
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copy(ifr[:], name)
_, _, errno := unix.Syscall(
unix.SYS_IOCTL,
uintptr(fd),
uintptr(unix.SIOCGIFINDEX),
uintptr(unsafe.Pointer(&ifr[0])),
)
if errno != 0 {
return 0, errno
}
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return *(*int32)(unsafe.Pointer(&ifr[unix.IFNAMSIZ])), nil
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}
func (tun *NativeTun) setMTU(n int) error {
name, err := tun.Name()
if err != nil {
return err
}
// open datagram socket
fd, err := unix.Socket(
unix.AF_INET,
unix.SOCK_DGRAM,
0,
)
if err != nil {
return err
}
defer unix.Close(fd)
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// do ioctl call
var ifr [ifReqSize]byte
copy(ifr[:], name)
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*(*uint32)(unsafe.Pointer(&ifr[unix.IFNAMSIZ])) = uint32(n)
_, _, errno := unix.Syscall(
unix.SYS_IOCTL,
uintptr(fd),
uintptr(unix.SIOCSIFMTU),
uintptr(unsafe.Pointer(&ifr[0])),
)
if errno != 0 {
return fmt.Errorf("failed to set MTU of TUN device: %w", errno)
}
return nil
}
func (tun *NativeTun) MTU() (int, error) {
name, err := tun.Name()
if err != nil {
return 0, err
}
// open datagram socket
fd, err := unix.Socket(
unix.AF_INET,
unix.SOCK_DGRAM,
0,
)
if err != nil {
return 0, err
}
defer unix.Close(fd)
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// do ioctl call
var ifr [ifReqSize]byte
copy(ifr[:], name)
_, _, errno := unix.Syscall(
unix.SYS_IOCTL,
uintptr(fd),
uintptr(unix.SIOCGIFMTU),
uintptr(unsafe.Pointer(&ifr[0])),
)
if errno != 0 {
return 0, fmt.Errorf("failed to get MTU of TUN device: %w", errno)
}
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return int(*(*int32)(unsafe.Pointer(&ifr[unix.IFNAMSIZ]))), nil
}
func (tun *NativeTun) Name() (string, error) {
tun.nameOnce.Do(tun.initNameCache)
return tun.nameCache, tun.nameErr
}
func (tun *NativeTun) initNameCache() {
tun.nameCache, tun.nameErr = tun.nameSlow()
}
func (tun *NativeTun) nameSlow() (string, error) {
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sysconn, err := tun.tunFile.SyscallConn()
if err != nil {
return "", err
}
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var ifr [ifReqSize]byte
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var errno syscall.Errno
err = sysconn.Control(func(fd uintptr) {
_, _, errno = unix.Syscall(
unix.SYS_IOCTL,
fd,
uintptr(unix.TUNGETIFF),
uintptr(unsafe.Pointer(&ifr[0])),
)
})
if err != nil {
return "", fmt.Errorf("failed to get name of TUN device: %w", err)
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}
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if errno != 0 {
return "", fmt.Errorf("failed to get name of TUN device: %w", errno)
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}
name := ifr[:]
if i := bytes.IndexByte(name, 0); i != -1 {
name = name[:i]
}
return string(name), nil
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}
func (tun *NativeTun) Write(buff []byte, offset int) (int, error) {
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if tun.nopi {
buff = buff[offset:]
} else {
// reserve space for header
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buff = buff[offset-4:]
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// add packet information header
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buff[0] = 0x00
buff[1] = 0x00
if buff[4]>>4 == ipv6.Version {
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buff[2] = 0x86
buff[3] = 0xdd
} else {
buff[2] = 0x08
buff[3] = 0x00
}
}
// write
return tun.tunFile.Write(buff)
}
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func (tun *NativeTun) Flush() error {
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// TODO: can flushing be implemented by buffering and using sendmmsg?
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return nil
}
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func (tun *NativeTun) Read(buff []byte, offset int) (int, error) {
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select {
case err := <-tun.errors:
return 0, err
default:
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if tun.nopi {
return tun.tunFile.Read(buff[offset:])
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} else {
buff := buff[offset-4:]
n, err := tun.tunFile.Read(buff[:])
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if n < 4 {
return 0, err
}
return n - 4, err
}
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}
}
func (tun *NativeTun) Events() chan Event {
return tun.events
}
func (tun *NativeTun) Close() error {
var err1, err2 error
tun.closeOnce.Do(func() {
if tun.statusListenersShutdown != nil {
close(tun.statusListenersShutdown)
if tun.netlinkCancel != nil {
err1 = tun.netlinkCancel.Cancel()
}
} else if tun.events != nil {
close(tun.events)
}
err2 = tun.tunFile.Close()
})
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if err1 != nil {
return err1
}
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return err2
}
func CreateTUN(name string, mtu int) (Device, error) {
nfd, err := unix.Open(cloneDevicePath, os.O_RDWR, 0)
if err != nil {
if os.IsNotExist(err) {
return nil, fmt.Errorf("CreateTUN(%q) failed; %s does not exist", name, cloneDevicePath)
}
return nil, err
}
var ifr [ifReqSize]byte
var flags uint16 = unix.IFF_TUN // | unix.IFF_NO_PI (disabled for TUN status hack)
nameBytes := []byte(name)
if len(nameBytes) >= unix.IFNAMSIZ {
return nil, fmt.Errorf("interface name too long: %w", unix.ENAMETOOLONG)
}
copy(ifr[:], nameBytes)
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*(*uint16)(unsafe.Pointer(&ifr[unix.IFNAMSIZ])) = flags
_, _, errno := unix.Syscall(
unix.SYS_IOCTL,
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uintptr(nfd),
uintptr(unix.TUNSETIFF),
uintptr(unsafe.Pointer(&ifr[0])),
)
if errno != 0 {
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return nil, errno
}
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err = unix.SetNonblock(nfd, true)
// Note that the above -- open,ioctl,nonblock -- must happen prior to handing it to netpoll as below this line.
fd := os.NewFile(uintptr(nfd), cloneDevicePath)
if err != nil {
return nil, err
}
return CreateTUNFromFile(fd, mtu)
}
func CreateTUNFromFile(file *os.File, mtu int) (Device, error) {
tun := &NativeTun{
tunFile: file,
events: make(chan Event, 5),
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errors: make(chan error, 5),
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statusListenersShutdown: make(chan struct{}),
nopi: false,
}
name, err := tun.Name()
if err != nil {
return nil, err
}
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// start event listener
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tun.index, err = getIFIndex(name)
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if err != nil {
return nil, err
}
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tun.netlinkSock, err = createNetlinkSocket()
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if err != nil {
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return nil, err
}
tun.netlinkCancel, err = rwcancel.NewRWCancel(tun.netlinkSock)
if err != nil {
unix.Close(tun.netlinkSock)
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return nil, err
}
tun.hackListenerClosed.Lock()
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go tun.routineNetlinkListener()
go tun.routineHackListener() // cross namespace
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err = tun.setMTU(mtu)
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if err != nil {
unix.Close(tun.netlinkSock)
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return nil, err
}
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return tun, nil
}
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func CreateUnmonitoredTUNFromFD(fd int) (Device, string, error) {
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err := unix.SetNonblock(fd, true)
if err != nil {
return nil, "", err
}
file := os.NewFile(uintptr(fd), "/dev/tun")
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tun := &NativeTun{
tunFile: file,
events: make(chan Event, 5),
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errors: make(chan error, 5),
nopi: true,
}
name, err := tun.Name()
if err != nil {
return nil, "", err
}
return tun, name, nil
}