Removed IFF_NO_PI from TUN linux

This change was needed for the Linux TUN status hack
to work properly (not increment the error counter).

This commit also updates the TUN interface to allow for
the construction / removal of the TUN info headers in-place.

4 files changed, 60 insertions, 18 deletions

diff --git a/src/receive.go b/src/receive.go
index f650cc9..dbd2813 100644
--- a/src/receive.go
+++ b/src/receive.go
@@ -243,13 +243,24 @@ func (device *Device) RoutineDecryption() {
 			counter := elem.packet[MessageTransportOffsetCounter:MessageTransportOffsetContent]
 			content := elem.packet[MessageTransportOffsetContent:]
 
+			// expand nonce
+
+			nonce[0x4] = counter[0x0]
+			nonce[0x5] = counter[0x1]
+			nonce[0x6] = counter[0x2]
+			nonce[0x7] = counter[0x3]
+
+			nonce[0x8] = counter[0x4]
+			nonce[0x9] = counter[0x5]
+			nonce[0xa] = counter[0x6]
+			nonce[0xb] = counter[0x7]
+
 			// decrypt and release to consumer
 
 			var err error
-			copy(nonce[4:], counter)
 			elem.counter = binary.LittleEndian.Uint64(counter)
 			elem.packet, err = elem.keyPair.receive.Open(
-				elem.buffer[:0],
+				content[:0],
 				nonce[:],
 				content,
 				nil,
@@ -495,6 +506,7 @@ func (peer *Peer) RoutineSequentialReceiver() {
 			// wait for decryption
 
 			elem.mutex.Lock()
+
 			if elem.IsDropped() {
 				continue
 			}
@@ -603,8 +615,11 @@ func (peer *Peer) RoutineSequentialReceiver() {
 
 			// write to tun device
 
+			offset := MessageTransportOffsetContent
 			atomic.AddUint64(&peer.stats.rxBytes, uint64(len(elem.packet)))
-			_, err := device.tun.device.Write(elem.packet)
+			_, err := device.tun.device.Write(
+				elem.buffer[:offset+len(elem.packet)],
+				offset)
 			device.PutMessageBuffer(elem.buffer)
 			if err != nil {
 				logError.Println("Failed to write packet to TUN device:", err)
diff --git a/src/send.go b/src/send.go
index 2919f2e..9537f5e 100644
--- a/src/send.go
+++ b/src/send.go
@@ -127,8 +127,9 @@ func (device *Device) RoutineReadFromTUN() {
 
 		// read packet
 
-		elem.packet = elem.buffer[MessageTransportHeaderSize:]
-		size, err := device.tun.device.Read(elem.packet)
+		offset := MessageTransportHeaderSize
+		size, err := device.tun.device.Read(elem.buffer[:], offset)
+
 		if err != nil {
 			logError.Println("Failed to read packet from TUN device:", err)
 			device.Close()
@@ -139,7 +140,7 @@ func (device *Device) RoutineReadFromTUN() {
 			continue
 		}
 
-		elem.packet = elem.packet[:size]
+		elem.packet = elem.buffer[offset : offset+size]
 
 		// lookup peer
 
diff --git a/src/tun.go b/src/tun.go
index 215022c..54253b4 100644
--- a/src/tun.go
+++ b/src/tun.go
@@ -16,13 +16,13 @@ const (
 )
 
 type TUNDevice interface {
-	File() *os.File            // returns the file descriptor of the device
-	Read([]byte) (int, error)  // read a packet from the device (without any additional headers)
-	Write([]byte) (int, error) // writes a packet to the device (without any additional headers)
-	MTU() (int, error)         // returns the MTU of the device
-	Name() string              // returns the current name
-	Events() chan TUNEvent     // returns a constant channel of events related to the device
-	Close() error              // stops the device and closes the event channel
+	File() *os.File                 // returns the file descriptor of the device
+	Read([]byte, int) (int, error)  // read a packet from the device (without any additional headers)
+	Write([]byte, int) (int, error) // writes a packet to the device (without any additional headers)
+	MTU() (int, error)              // returns the MTU of the device
+	Name() string                   // returns the current name
+	Events() chan TUNEvent          // returns a constant channel of events related to the device
+	Close() error                   // stops the device and closes the event channel
 }
 
 func (device *Device) RoutineTUNEventReader() {
diff --git a/src/tun_linux.go b/src/tun_linux.go
index 8a5d53b..daa2462 100644
--- a/src/tun_linux.go
+++ b/src/tun_linux.go
@@ -7,6 +7,7 @@ import (
 	"encoding/binary"
 	"errors"
 	"fmt"
+	"golang.org/x/net/ipv6"
 	"golang.org/x/sys/unix"
 	"net"
 	"os"
@@ -249,16 +250,41 @@ func (tun *NativeTun) MTU() (int, error) {
 	return int(val), nil
 }
 
-func (tun *NativeTun) Write(d []byte) (int, error) {
-	return tun.fd.Write(d)
+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
+
+	if buff[4] == ipv6.Version<<4 {
+		buff[2] = 0x86
+		buff[3] = 0xdd
+	} else {
+		buff[2] = 0x08
+		buff[3] = 0x00
+	}
+
+	// write
+
+	return tun.fd.Write(buff)
 }
 
-func (tun *NativeTun) Read(d []byte) (int, error) {
+func (tun *NativeTun) Read(buff []byte, offset int) (int, error) {
 	select {
 	case err := <-tun.errors:
 		return 0, err
 	default:
-		return tun.fd.Read(d)
+		buff := buff[offset-4:]
+		n, err := tun.fd.Read(buff[:])
+		if n < 4 {
+			return 0, err
+		}
+		return n - 4, err
 	}
 }
 
@@ -306,7 +332,7 @@ func CreateTUN(name string) (TUNDevice, error) {
 	// create new device
 
 	var ifr [IFReqSize]byte
-	var flags uint16 = unix.IFF_TUN | unix.IFF_NO_PI
+	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")