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|
package main
/* Implementation of the TUN device interface for linux
*/
import (
"encoding/binary"
"errors"
"fmt"
"golang.org/x/sys/unix"
"net"
"os"
"strings"
"unsafe"
)
// #include <string.h>
// #include <unistd.h>
// #include <net/if.h>
// #include <netinet/in.h>
// #include <linux/netlink.h>
// #include <linux/rtnetlink.h>
//
// /* Creates a netlink socket
// * listening to the RTMGRP_LINK multicast group
// */
//
// int bind_rtmgrp() {
// int nl_sock = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
// if (nl_sock < 0)
// return -1;
//
// struct sockaddr_nl addr;
// memset ((void *) &addr, 0, sizeof (addr));
// addr.nl_family = AF_NETLINK;
// addr.nl_pid = getpid ();
// addr.nl_groups = RTMGRP_LINK | RTMGRP_IPV4_IFADDR | RTMGRP_IPV6_IFADDR;
//
// if (bind(nl_sock, (struct sockaddr *) &addr, sizeof (addr)) < 0)
// return -1;
//
// return nl_sock;
// }
import "C"
const (
CloneDevicePath = "/dev/net/tun"
IFReqSize = unix.IFNAMSIZ + 64
)
type NativeTun struct {
fd *os.File
index int32 // if index
name string // name of interface
errors chan error // async error handling
events chan TUNEvent // device related events
}
func (tun *NativeTun) RoutineNetlinkListener() {
sock := int(C.bind_rtmgrp())
if sock < 0 {
tun.errors <- errors.New("Failed to create netlink event listener")
return
}
for msg := make([]byte, 1<<16); ; {
msgn, _, _, _, err := unix.Recvmsg(sock, msg[:], nil, 0)
if err != nil {
tun.errors <- fmt.Errorf("Failed to receive netlink message: %s", err.Error())
return
}
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]))
if info.Index != tun.index {
// not our interface
continue
}
if info.Flags&unix.IFF_RUNNING != 0 {
tun.events <- TUNEventUp
}
if info.Flags&unix.IFF_RUNNING == 0 {
tun.events <- TUNEventDown
}
remain = remain[hdr.Len:]
default:
remain = remain[hdr.Len:]
}
}
}
}
func (tun *NativeTun) isUp() (bool, error) {
inter, err := net.InterfaceByName(tun.name)
return inter.Flags&net.FlagUp != 0, err
}
func (tun *NativeTun) Name() string {
return tun.name
}
func toInt32(val []byte) int32 {
n := binary.LittleEndian.Uint32(val[:4])
if n >= (1 << 31) {
return -int32(^n) - 1
}
return int32(n)
}
func getDummySock() (int, error) {
return unix.Socket(
unix.AF_INET,
unix.SOCK_DGRAM,
0,
)
}
func getIFIndex(name string) (int32, error) {
fd, err := getDummySock()
if err != nil {
return 0, err
}
defer unix.Close(fd)
var ifr [IFReqSize]byte
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
}
return toInt32(ifr[unix.IFNAMSIZ:]), nil
}
func (tun *NativeTun) setMTU(n int) error {
// open datagram socket
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 [IFReqSize]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 errors.New("Failed to set MTU of TUN device")
}
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 [IFReqSize]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, errors.New("Failed to get MTU of TUN device")
}
// 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
}
func (tun *NativeTun) Write(d []byte) (int, error) {
return tun.fd.Write(d)
}
func (tun *NativeTun) Read(d []byte) (int, error) {
select {
case err := <-tun.errors:
return 0, err
default:
return tun.fd.Read(d)
}
}
func (tun *NativeTun) Events() chan TUNEvent {
return tun.events
}
func (tun *NativeTun) Close() error {
return nil
}
func CreateTUN(name string) (TUNDevice, error) {
// open clone device
fd, err := os.OpenFile(CloneDevicePath, os.O_RDWR, 0)
if err != nil {
return nil, err
}
// create new device
var ifr [IFReqSize]byte
var flags uint16 = unix.IFF_TUN | unix.IFF_NO_PI
nameBytes := []byte(name)
if len(nameBytes) >= unix.IFNAMSIZ {
return nil, errors.New("Interface name too long")
}
copy(ifr[:], nameBytes)
binary.LittleEndian.PutUint16(ifr[16:], flags)
_, _, errno := unix.Syscall(
unix.SYS_IOCTL,
uintptr(fd.Fd()),
uintptr(unix.TUNSETIFF),
uintptr(unsafe.Pointer(&ifr[0])),
)
if errno != 0 {
return nil, errno
}
// read (new) name of interface
newName := string(ifr[:])
newName = newName[:strings.Index(newName, "\000")]
device := &NativeTun{
fd: fd,
name: newName,
events: make(chan TUNEvent, 5),
errors: make(chan error, 5),
}
// start event listener
device.index, err = getIFIndex(device.name)
if err != nil {
return nil, err
}
go device.RoutineNetlinkListener()
// set default MTU
return device, device.setMTU(DefaultMTU)
}
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