EtherGuard-VPN/tun_darwin.go
Jason A. Donenfeld 2326d6a4d7 Odds and ends
2018-05-13 19:34:28 +02:00

307 lines
5.4 KiB
Go

/* SPDX-License-Identifier: GPL-2.0
*
* Copyright (C) 2017-2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
*/
package main
import (
"encoding/binary"
"fmt"
"golang.org/x/net/ipv6"
"golang.org/x/sys/unix"
"net"
"os"
"time"
"unsafe"
)
const utunControlName = "com.apple.net.utun_control"
// _CTLIOCGINFO value derived from /usr/include/sys/{kern_control,ioccom}.h
const _CTLIOCGINFO = (0x40000000 | 0x80000000) | ((100 & 0x1fff) << 16) | uint32(byte('N'))<<8 | 3
// sockaddr_ctl specifeid in /usr/include/sys/kern_control.h
type sockaddrCtl struct {
scLen uint8
scFamily uint8
ssSysaddr uint16
scID uint32
scUnit uint32
scReserved [5]uint32
}
// NativeTun is a hack to work around the first 4 bytes "packet
// information" because there doesn't seem to be an IFF_NO_PI for darwin.
type NativeTun struct {
name string
fd *os.File
mtu int
events chan TUNEvent
errors chan error
}
var sockaddrCtlSize uintptr = 32
func CreateTUN(name string) (TUNDevice, error) {
ifIndex := -1
if name != "utun" {
fmt.Sscanf(name, "utun%d", &ifIndex)
if ifIndex < 0 {
return nil, fmt.Errorf("Interface name must be utun[0-9]*")
}
}
fd, err := unix.Socket(unix.AF_SYSTEM, unix.SOCK_DGRAM, 2)
if err != nil {
return nil, err
}
var ctlInfo = &struct {
ctlID uint32
ctlName [96]byte
}{}
copy(ctlInfo.ctlName[:], []byte(utunControlName))
_, _, errno := unix.Syscall(
unix.SYS_IOCTL,
uintptr(fd),
uintptr(_CTLIOCGINFO),
uintptr(unsafe.Pointer(ctlInfo)),
)
if errno != 0 {
return nil, fmt.Errorf("_CTLIOCGINFO: %v", errno)
}
sc := sockaddrCtl{
scLen: uint8(sockaddrCtlSize),
scFamily: unix.AF_SYSTEM,
ssSysaddr: 2,
scID: ctlInfo.ctlID,
scUnit: uint32(ifIndex) + 1,
}
scPointer := unsafe.Pointer(&sc)
_, _, errno = unix.RawSyscall(
unix.SYS_CONNECT,
uintptr(fd),
uintptr(scPointer),
uintptr(sockaddrCtlSize),
)
if errno != 0 {
return nil, fmt.Errorf("SYS_CONNECT: %v", errno)
}
tun, err := CreateTUNFromFile(os.NewFile(uintptr(fd), ""))
if err == nil && name == "utun" {
fmt.Printf("OS assigned interface: %s\n", tun.(*NativeTun).name)
}
return tun, err
}
func CreateTUNFromFile(file *os.File) (TUNDevice, error) {
tun := &NativeTun{
fd: file,
mtu: 1500,
events: make(chan TUNEvent, 10),
errors: make(chan error, 1),
}
_, err := tun.Name()
if err != nil {
return nil, err
}
// TODO: Fix this very naive implementation
go func(tun *NativeTun) {
var (
statusUp bool
statusMTU int
)
for ; ; time.Sleep(time.Second) {
intr, err := net.InterfaceByName(tun.name)
if err != nil {
tun.errors <- err
return
}
// Up / Down event
up := (intr.Flags & net.FlagUp) != 0
if up != statusUp && up {
tun.events <- TUNEventUp
}
if up != statusUp && !up {
tun.events <- TUNEventDown
}
statusUp = up
// MTU changes
if intr.MTU != statusMTU {
tun.events <- TUNEventMTUUpdate
}
statusMTU = intr.MTU
}
}(tun)
// set default MTU
err = tun.setMTU(DefaultMTU)
return tun, err
}
func (tun *NativeTun) Name() (string, error) {
var ifName struct {
name [16]byte
}
ifNameSize := uintptr(16)
_, _, errno := unix.Syscall6(
unix.SYS_GETSOCKOPT,
uintptr(tun.fd.Fd()),
2, /* #define SYSPROTO_CONTROL 2 */
2, /* #define UTUN_OPT_IFNAME 2 */
uintptr(unsafe.Pointer(&ifName)),
uintptr(unsafe.Pointer(&ifNameSize)), 0)
if errno != 0 {
return "", fmt.Errorf("SYS_GETSOCKOPT: %v", errno)
}
tun.name = string(ifName.name[:ifNameSize-1])
return tun.name, nil
}
func (tun *NativeTun) File() *os.File {
return tun.fd
}
func (tun *NativeTun) Events() chan TUNEvent {
return tun.events
}
func (tun *NativeTun) Read(buff []byte, offset int) (int, error) {
buff = buff[offset-4:]
n, err := tun.fd.Read(buff[:])
if n < 4 {
return 0, err
}
return n - 4, err
}
func (tun *NativeTun) Write(buff []byte, offset int) (int, error) {
// reserve space for header
buff = buff[offset-4:]
// add packet information header
buff[0] = 0x00
buff[1] = 0x00
buff[2] = 0x00
if buff[4]>>4 == ipv6.Version {
buff[3] = unix.AF_INET6
} else {
buff[3] = unix.AF_INET
}
// write
return tun.fd.Write(buff)
}
func (tun *NativeTun) Close() error {
err := tun.fd.Close()
close(tun.events)
return err
}
func (tun *NativeTun) setMTU(n int) error {
// open datagram socket
var fd int
fd, err := unix.Socket(
unix.AF_INET,
unix.SOCK_DGRAM,
0,
)
if err != nil {
return err
}
defer unix.Close(fd)
// do ioctl call
var ifr [32]byte
copy(ifr[:], tun.name)
binary.LittleEndian.PutUint32(ifr[16:20], 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 on %s", tun.name)
}
return nil
}
func (tun *NativeTun) MTU() (int, error) {
// open datagram socket
fd, err := unix.Socket(
unix.AF_INET,
unix.SOCK_DGRAM,
0,
)
if err != nil {
return 0, err
}
defer unix.Close(fd)
// do ioctl call
var ifr [64]byte
copy(ifr[:], tun.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 on %s", tun.name)
}
// convert result to signed 32-bit int
val := binary.LittleEndian.Uint32(ifr[16:20])
if val >= (1 << 31) {
return int(val-(1<<31)) - (1 << 31), nil
}
return int(val), nil
}