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 fmt.Sscanf(name, "utun%d", &ifIndex) if ifIndex < 0 { return nil, fmt.Errorf("error parsing interface name %s, must be utun[0-9]+", name) } 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) } return CreateTUNFromFile(os.NewFile(uintptr(fd), "")) } 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 { return tun.fd.Close() } 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 }