1 files changed, 468 insertions, 0 deletions
diff --git a/tun/tun_linux.go b/tun/tun_linux.go
new file mode 100644
index 0000000..acfb942
--- /dev/null
+++ b/tun/tun_linux.go
@@ -0,0 +1,468 @@
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * Copyright (C) 2017-2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ * Copyright (C) 2017-2018 Mathias N. Hall-Andersen <mathias@hall-andersen.dk>.
+ */
+
+/* Copyright 2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved. */
+
+package tun
+
+/* Implementation of the TUN device interface for linux
+ */
+
+import (
+	"../rwcancel"
+	"bytes"
+	"errors"
+	"fmt"
+	"golang.org/x/net/ipv6"
+	"golang.org/x/sys/unix"
+	"net"
+	"os"
+	"strconv"
+	"sync"
+	"time"
+	"unsafe"
+)
+
+const (
+	cloneDevicePath = "/dev/net/tun"
+	ifReqSize       = unix.IFNAMSIZ + 64
+)
+
+type nativeTun struct {
+	fd                      *os.File
+	fdCancel                *rwcancel.RWCancel
+	index                   int32         // if index
+	name                    string        // name of interface
+	errors                  chan error    // async error handling
+	events                  chan TUNEvent // device related events
+	nopi                    bool          // the device was pased IFF_NO_PI
+	netlinkSock             int
+	netlinkCancel           *rwcancel.RWCancel
+	hackListenerClosed      sync.Mutex
+	statusListenersShutdown chan struct{}
+}
+
+func (tun *nativeTun) File() *os.File {
+	return tun.fd
+}
+
+func (tun *nativeTun) routineHackListener() {
+	defer tun.hackListenerClosed.Unlock()
+	/* 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.
+	 */
+	fd := int(tun.fd.Fd())
+	for {
+		_, err := unix.Write(fd, nil)
+		switch err {
+		case unix.EINVAL:
+			tun.events <- TUNEventUp
+		case unix.EIO:
+			tun.events <- TUNEventDown
+		default:
+			return
+		}
+		select {
+		case <-time.After(time.Second):
+		case <-tun.statusListenersShutdown:
+			return
+		}
+	}
+}
+
+func createNetlinkSocket() (int, error) {
+	sock, err := unix.Socket(unix.AF_NETLINK, unix.SOCK_RAW, unix.NETLINK_ROUTE)
+	if err != nil {
+		return -1, err
+	}
+	saddr := &unix.SockaddrNetlink{
+		Family: unix.AF_NETLINK,
+		Groups: uint32((1 << (unix.RTNLGRP_LINK - 1)) | (1 << (unix.RTNLGRP_IPV4_IFADDR - 1)) | (1 << (unix.RTNLGRP_IPV6_IFADDR - 1))),
+	}
+	err = unix.Bind(sock, saddr)
+	if err != nil {
+		return -1, err
+	}
+	return sock, nil
+}
+
+func (tun *nativeTun) routineNetlinkListener() {
+	defer func() {
+		unix.Close(tun.netlinkSock)
+		tun.hackListenerClosed.Lock()
+		close(tun.events)
+	}()
+
+	for msg := make([]byte, 1<<16); ; {
+
+		var err error
+		var msgn int
+		for {
+			msgn, _, _, _, err = unix.Recvmsg(tun.netlinkSock, msg[:], nil, 0)
+			if err == nil || !rwcancel.ErrorIsEAGAIN(err) {
+				break
+			}
+			if !tun.netlinkCancel.ReadyRead() {
+				tun.errors <- fmt.Errorf("netlink socket closed: %s", err.Error())
+				return
+			}
+		}
+		if err != nil {
+			tun.errors <- fmt.Errorf("failed to receive netlink message: %s", err.Error())
+			return
+		}
+
+		select {
+		case <-tun.statusListenersShutdown:
+			return
+		default:
+		}
+
+		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:]
+
+				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
+				}
+
+				tun.events <- TUNEventMTUUpdate
+
+			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 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 *(*int32)(unsafe.Pointer(&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)
+	*(*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 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: " + strconv.FormatInt(int64(errno), 10))
+	}
+
+	return int(*(*int32)(unsafe.Pointer(&ifr[unix.IFNAMSIZ]))), nil
+}
+
+func (tun *nativeTun) Name() (string, error) {
+
+	var ifr [ifReqSize]byte
+	_, _, errno := unix.Syscall(
+		unix.SYS_IOCTL,
+		tun.fd.Fd(),
+		uintptr(unix.TUNGETIFF),
+		uintptr(unsafe.Pointer(&ifr[0])),
+	)
+	if errno != 0 {
+		return "", errors.New("failed to get name of TUN device: " + strconv.FormatInt(int64(errno), 10))
+	}
+	nullStr := ifr[:]
+	i := bytes.IndexByte(nullStr, 0)
+	if i != -1 {
+		nullStr = nullStr[:i]
+	}
+	tun.name = string(nullStr)
+	return tun.name, nil
+}
+
+func (tun *nativeTun) Write(buff []byte, offset int) (int, error) {
+
+	if tun.nopi {
+		buff = buff[offset:]
+	} else {
+		// reserve space for header
+
+		buff = buff[offset-4:]
+
+		// add packet information header
+
+		buff[0] = 0x00
+		buff[1] = 0x00
+
+		if buff[4]>>4 == ipv6.Version {
+			buff[2] = 0x86
+			buff[3] = 0xdd
+		} else {
+			buff[2] = 0x08
+			buff[3] = 0x00
+		}
+	}
+
+	// write
+
+	return tun.fd.Write(buff)
+}
+
+func (tun *nativeTun) doRead(buff []byte, offset int) (int, error) {
+	select {
+	case err := <-tun.errors:
+		return 0, err
+	default:
+		if tun.nopi {
+			return tun.fd.Read(buff[offset:])
+		} else {
+			buff := buff[offset-4:]
+			n, err := tun.fd.Read(buff[:])
+			if n < 4 {
+				return 0, err
+			}
+			return n - 4, err
+		}
+	}
+}
+
+func (tun *nativeTun) Read(buff []byte, offset int) (int, error) {
+	for {
+		n, err := tun.doRead(buff, offset)
+		if err == nil || !rwcancel.ErrorIsEAGAIN(err) {
+			return n, err
+		}
+		if !tun.fdCancel.ReadyRead() {
+			return 0, errors.New("tun device closed")
+		}
+	}
+}
+
+func (tun *nativeTun) Events() chan TUNEvent {
+	return tun.events
+}
+
+func (tun *nativeTun) Close() error {
+	var err1 error
+	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.fd.Close()
+	err3 := tun.fdCancel.Cancel()
+
+	if err1 != nil {
+		return err1
+	}
+	if err2 != nil {
+		return err2
+	}
+	return err3
+}
+
+func CreateTUN(name string, mtu int) (TUNDevice, error) {
+
+	// open clone device
+
+	// HACK: we open it as a raw Fd first, so that f.nonblock=false
+	// when we make it into a file object.
+	nfd, err := unix.Open(cloneDevicePath, os.O_RDWR, 0)
+	if err != nil {
+		return nil, err
+	}
+
+	err = unix.SetNonblock(nfd, true)
+	if err != nil {
+		return nil, err
+	}
+
+	fd := os.NewFile(uintptr(nfd), cloneDevicePath)
+	if err != nil {
+		return nil, err
+	}
+
+	// create new device
+
+	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, errors.New("interface name too long")
+	}
+	copy(ifr[:], nameBytes)
+	*(*uint16)(unsafe.Pointer(&ifr[unix.IFNAMSIZ])) = flags
+
+	_, _, errno := unix.Syscall(
+		unix.SYS_IOCTL,
+		fd.Fd(),
+		uintptr(unix.TUNSETIFF),
+		uintptr(unsafe.Pointer(&ifr[0])),
+	)
+	if errno != 0 {
+		return nil, errno
+	}
+
+	return CreateTUNFromFile(fd, mtu)
+}
+
+func CreateTUNFromFile(file *os.File, mtu int) (TUNDevice, error) {
+	tun := &nativeTun{
+		fd:                      file,
+		events:                  make(chan TUNEvent, 5),
+		errors:                  make(chan error, 5),
+		statusListenersShutdown: make(chan struct{}),
+		nopi: false,
+	}
+	var err error
+
+	tun.fdCancel, err = rwcancel.NewRWCancel(int(file.Fd()))
+	if err != nil {
+		tun.fd.Close()
+		return nil, err
+	}
+
+	_, err = tun.Name()
+	if err != nil {
+		tun.fd.Close()
+		return nil, err
+	}
+
+	// start event listener
+
+	tun.index, err = getIFIndex(tun.name)
+	if err != nil {
+		return nil, err
+	}
+
+	tun.netlinkSock, err = createNetlinkSocket()
+	if err != nil {
+		tun.fd.Close()
+		return nil, err
+	}
+	tun.netlinkCancel, err = rwcancel.NewRWCancel(tun.netlinkSock)
+	if err != nil {
+		tun.fd.Close()
+		return nil, err
+	}
+
+	tun.hackListenerClosed.Lock()
+	go tun.routineNetlinkListener()
+	go tun.routineHackListener() // cross namespace
+
+	err = tun.setMTU(mtu)
+	if err != nil {
+		tun.Close()
+		return nil, err
+	}
+
+	return tun, nil
+}