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vmnet.go
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vmnet.go
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package vmnet
import (
"bytes"
"context"
"encoding/binary"
"errors"
"fmt"
"io"
"net"
"time"
"github.com/google/uuid"
)
// Vmnet describes a "vmnet protocol" connection which allows ethernet frames to be
// sent to and received by vpnkit.
type Vmnet struct {
conn net.Conn
remoteVersion *InitMessage
}
// New constructs an instance of Vmnet.
func New(ctx context.Context, path string) (*Vmnet, error) {
d := &net.Dialer{}
conn, err := d.DialContext(ctx, "unix", path)
if err != nil {
return nil, err
}
var remoteVersion *InitMessage
vmnet := &Vmnet{conn, remoteVersion}
err = vmnet.negotiate()
if err != nil {
return nil, err
}
return vmnet, err
}
// Close closes the connection.
func (v *Vmnet) Close() error {
return v.conn.Close()
}
// InitMessage is used for the initial version exchange
type InitMessage struct {
magic [5]byte
version uint32
commit [40]byte
}
// String returns a human-readable string.
func (m *InitMessage) String() string {
return fmt.Sprintf("magic=%v version=%d commit=%v", m.magic, m.version, m.commit)
}
// defaultInitMessage is the init message we will send to vpnkit
func defaultInitMessage() *InitMessage {
magic := [5]byte{'V', 'M', 'N', '3', 'T'}
version := uint32(22)
var commit [40]byte
copy(commit[:], []byte("0123456789012345678901234567890123456789"))
return &InitMessage{magic, version, commit}
}
// Write marshals an init message to a connection
func (m *InitMessage) Write(c net.Conn) error {
if err := binary.Write(c, binary.LittleEndian, m.magic); err != nil {
return err
}
if err := binary.Write(c, binary.LittleEndian, m.version); err != nil {
return err
}
if err := binary.Write(c, binary.LittleEndian, m.commit); err != nil {
return err
}
return nil
}
// readInitMessage unmarshals an init message from a connection
func (v *Vmnet) readInitMessage() (*InitMessage, error) {
m := defaultInitMessage()
if err := binary.Read(v.conn, binary.LittleEndian, &m.magic); err != nil {
return nil, err
}
if err := binary.Read(v.conn, binary.LittleEndian, &m.version); err != nil {
return nil, err
}
if err := binary.Read(v.conn, binary.LittleEndian, &m.commit); err != nil {
return nil, err
}
return m, nil
}
func (v *Vmnet) negotiate() error {
m := defaultInitMessage()
if err := m.Write(v.conn); err != nil {
return err
}
remoteVersion, err := v.readInitMessage()
if err != nil {
return err
}
v.remoteVersion = remoteVersion
return nil
}
// Ethernet requests the creation of a network connection with a given
// uuid and optional IP
type Ethernet struct {
uuid uuid.UUID
ip net.IP
}
// NewEthernet creates an Ethernet frame
func NewEthernet(uuid uuid.UUID, ip net.IP) *Ethernet {
return &Ethernet{uuid, ip}
}
// Write marshals an Ethernet message
func (m *Ethernet) Write(c net.Conn) error {
ty := uint8(1)
if m.ip != nil {
ty = uint8(8)
}
if err := binary.Write(c, binary.LittleEndian, ty); err != nil {
return err
}
u, err := m.uuid.MarshalText()
if err != nil {
return err
}
if err := binary.Write(c, binary.LittleEndian, u); err != nil {
return err
}
ip := uint32(0)
if m.ip != nil {
ip = binary.BigEndian.Uint32(m.ip.To4())
}
// The protocol uses little endian, not network endian
if err := binary.Write(c, binary.LittleEndian, ip); err != nil {
return err
}
return nil
}
// Vif represents an Ethernet device
type Vif struct {
MTU uint16
MaxPacketSize uint16
ClientMAC net.HardwareAddr
IP net.IP
conn net.Conn
}
func (v *Vmnet) readVif() (*Vif, error) {
var MTU, MaxPacketSize uint16
if err := binary.Read(v.conn, binary.LittleEndian, &MTU); err != nil {
return nil, err
}
if err := binary.Read(v.conn, binary.LittleEndian, &MaxPacketSize); err != nil {
return nil, err
}
var mac [6]byte
if err := binary.Read(v.conn, binary.LittleEndian, &mac); err != nil {
return nil, err
}
padding := make([]byte, 1+256-6-2-2)
if err := binary.Read(v.conn, binary.LittleEndian, &padding); err != nil {
return nil, err
}
ClientMAC := mac[:]
conn := v.conn
var IP net.IP
return &Vif{MTU, MaxPacketSize, ClientMAC, IP, conn}, nil
}
// ConnectVif returns a connected network interface with the given uuid.
func (v *Vmnet) ConnectVif(uuid uuid.UUID) (*Vif, error) {
e := NewEthernet(uuid, nil)
if err := e.Write(v.conn); err != nil {
return nil, err
}
var responseType uint8
if err := binary.Read(v.conn, binary.LittleEndian, &responseType); err != nil {
return nil, err
}
switch responseType {
case 1:
vif, err := v.readVif()
if err != nil {
return nil, err
}
IP, err := vif.dhcp()
if err != nil {
return nil, err
}
vif.IP = IP
return vif, err
default:
var len uint8
if err := binary.Read(v.conn, binary.LittleEndian, &len); err != nil {
return nil, err
}
message := make([]byte, len)
if err := binary.Read(v.conn, binary.LittleEndian, &message); err != nil {
return nil, err
}
return nil, errors.New(string(message))
}
}
// ConnectVifIP returns a connected network interface with the given uuid
// and IP. If the IP is already in use then return an error.
func (v *Vmnet) ConnectVifIP(uuid uuid.UUID, IP net.IP) (*Vif, error) {
e := NewEthernet(uuid, IP)
if err := e.Write(v.conn); err != nil {
return nil, err
}
var responseType uint8
if err := binary.Read(v.conn, binary.LittleEndian, &responseType); err != nil {
return nil, err
}
switch responseType {
case 1:
vif, err := v.readVif()
if err != nil {
return nil, err
}
vif.IP = IP
return vif, err
default:
var len uint8
if err := binary.Read(v.conn, binary.LittleEndian, &len); err != nil {
return nil, err
}
message := make([]byte, len)
if err := binary.Read(v.conn, binary.LittleEndian, &message); err != nil {
return nil, err
}
return nil, errors.New(string(message))
}
}
// Write writes a packet to a Vif
func (v *Vif) Write(packet []byte) error {
len := uint16(len(packet))
if err := binary.Write(v.conn, binary.LittleEndian, len); err != nil {
return err
}
if err := binary.Write(v.conn, binary.LittleEndian, packet); err != nil {
return err
}
return nil
}
// Read reads the next packet from a Vif
func (v *Vif) Read() ([]byte, error) {
var len uint16
if err := binary.Read(v.conn, binary.LittleEndian, &len); err != nil {
return nil, err
}
packet := make([]byte, len)
if err := binary.Read(v.conn, binary.LittleEndian, &packet); err != nil {
return nil, err
}
return packet, nil
}
// PcapWriter writes pcap-formatted packet streams
type PcapWriter struct {
w io.Writer
snaplen uint32
}
// NewPcapWriter creates a PcapWriter and writes the initial header
func NewPcapWriter(w io.Writer) (*PcapWriter, error) {
magic := uint32(0xa1b2c3d4)
major := uint16(2)
minor := uint16(4)
thiszone := uint32(0) // GMT to local correction
sigfigs := uint32(0) // accuracy of local timestamps
snaplen := uint32(1500) // max length of captured packets, in octets
network := uint32(1) // ethernet
if err := binary.Write(w, binary.LittleEndian, magic); err != nil {
return nil, err
}
if err := binary.Write(w, binary.LittleEndian, major); err != nil {
return nil, err
}
if err := binary.Write(w, binary.LittleEndian, minor); err != nil {
return nil, err
}
if err := binary.Write(w, binary.LittleEndian, thiszone); err != nil {
return nil, err
}
if err := binary.Write(w, binary.LittleEndian, sigfigs); err != nil {
return nil, err
}
if err := binary.Write(w, binary.LittleEndian, snaplen); err != nil {
return nil, err
}
if err := binary.Write(w, binary.LittleEndian, network); err != nil {
return nil, err
}
return &PcapWriter{w, snaplen}, nil
}
// Write appends a packet with a pcap-format header
func (p *PcapWriter) Write(packet []byte) error {
stamp := time.Now()
s := uint32(stamp.Second())
us := uint32(stamp.Nanosecond() / 1000)
actualLen := uint32(len(packet))
if err := binary.Write(p.w, binary.LittleEndian, s); err != nil {
return err
}
if err := binary.Write(p.w, binary.LittleEndian, us); err != nil {
return err
}
toWrite := packet[:]
if actualLen > p.snaplen {
toWrite = toWrite[0:p.snaplen]
}
caplen := uint32(len(toWrite))
if err := binary.Write(p.w, binary.LittleEndian, caplen); err != nil {
return err
}
if err := binary.Write(p.w, binary.LittleEndian, actualLen); err != nil {
return err
}
if err := binary.Write(p.w, binary.LittleEndian, toWrite); err != nil {
return err
}
return nil
}
// EthernetFrame is an ethernet frame
type EthernetFrame struct {
Dst net.HardwareAddr
Src net.HardwareAddr
Type uint16
Data []byte
}
// NewEthernetFrame constructs an Ethernet frame
func NewEthernetFrame(Dst, Src net.HardwareAddr, Type uint16) *EthernetFrame {
Data := make([]byte, 0)
return &EthernetFrame{Dst, Src, Type, Data}
}
func (e *EthernetFrame) setData(data []byte) {
e.Data = data
}
// Write marshals an Ethernet frame
func (e *EthernetFrame) Write(w io.Writer) error {
if err := binary.Write(w, binary.BigEndian, e.Dst); err != nil {
return err
}
if err := binary.Write(w, binary.BigEndian, e.Src); err != nil {
return err
}
if err := binary.Write(w, binary.BigEndian, e.Type); err != nil {
return err
}
if err := binary.Write(w, binary.BigEndian, e.Data); err != nil {
return err
}
return nil
}
// ParseEthernetFrame parses the ethernet frame
func ParseEthernetFrame(frame []byte) (*EthernetFrame, error) {
if len(frame) < (6 + 6 + 2) {
return nil, errors.New("Ethernet frame is too small")
}
Dst := frame[0:6]
Src := frame[6:12]
Type := uint16(frame[12])<<8 + uint16(frame[13])
Data := frame[14:]
return &EthernetFrame{Dst, Src, Type, Data}, nil
}
// Bytes returns the marshalled ethernet frame
func (e *EthernetFrame) Bytes() []byte {
buf := bytes.NewBufferString("")
if err := e.Write(buf); err != nil {
panic(err)
}
return buf.Bytes()
}
// Ipv4 is an IPv4 frame
type Ipv4 struct {
Dst net.IP
Src net.IP
Data []byte
Checksum uint16
}
// NewIpv4 constructs a new empty IPv4 packet
func NewIpv4(Dst, Src net.IP) *Ipv4 {
Checksum := uint16(0)
Data := make([]byte, 0)
return &Ipv4{Dst, Src, Data, Checksum}
}
// ParseIpv4 parses an IP packet
func ParseIpv4(packet []byte) (*Ipv4, error) {
if len(packet) < 20 {
return nil, errors.New("IPv4 packet too small")
}
ihl := int((packet[0] & 0xf) * 4) // in octets
if len(packet) < ihl {
return nil, errors.New("IPv4 packet too small")
}
Dst := packet[12:16]
Src := packet[16:20]
Data := packet[ihl:]
Checksum := uint16(0) // assume offload
return &Ipv4{Dst, Src, Data, Checksum}, nil
}
func (i *Ipv4) setData(data []byte) {
i.Data = data
i.Checksum = uint16(0) // as if we were using offload
}
// HeaderBytes returns the marshalled form of the IPv4 header
func (i *Ipv4) HeaderBytes() []byte {
len := len(i.Data) + 20
length := [2]byte{byte(len >> 8), byte(len & 0xff)}
checksum := [2]byte{byte(i.Checksum >> 8), byte(i.Checksum & 0xff)}
return []byte{
0x45, // version + IHL
0x00, // DSCP + ECN
length[0], length[1], // total length
0x7f, 0x61, // Identification
0x00, 0x00, // Flags + Fragment offset
0x40, // TTL
0x11, // Protocol
checksum[0], checksum[1],
0x00, 0x00, 0x00, 0x00, // source
0xff, 0xff, 0xff, 0xff, // destination
}
}
// Bytes returns the marshalled IPv4 packet
func (i *Ipv4) Bytes() []byte {
header := i.HeaderBytes()
return append(header, i.Data...)
}
// Udpv4 is a Udpv4 frame
type Udpv4 struct {
Src uint16
Dst uint16
Data []byte
Checksum uint16
}
// NewUdpv4 constructs a Udpv4 frame
func NewUdpv4(ipv4 *Ipv4, Dst, Src uint16, Data []byte) *Udpv4 {
Checksum := uint16(0)
return &Udpv4{Dst, Src, Data, Checksum}
}
// ParseUdpv4 parses a Udpv4 packet
func ParseUdpv4(packet []byte) (*Udpv4, error) {
if len(packet) < 8 {
return nil, errors.New("UDPv4 is too short")
}
Src := uint16(packet[0])<<8 + uint16(packet[1])
Dst := uint16(packet[2])<<8 + uint16(packet[3])
Checksum := uint16(packet[6])<<8 + uint16(packet[7])
Data := packet[8:]
return &Udpv4{Src, Dst, Data, Checksum}, nil
}
// Write marshalls a Udpv4 frame
func (u *Udpv4) Write(w io.Writer) error {
if err := binary.Write(w, binary.BigEndian, u.Src); err != nil {
return err
}
if err := binary.Write(w, binary.BigEndian, u.Dst); err != nil {
return err
}
length := uint16(8 + len(u.Data))
if err := binary.Write(w, binary.BigEndian, length); err != nil {
return err
}
if err := binary.Write(w, binary.BigEndian, u.Checksum); err != nil {
return err
}
if err := binary.Write(w, binary.BigEndian, u.Data); err != nil {
return err
}
return nil
}
// Bytes returns the marshalled Udpv4 frame
func (u *Udpv4) Bytes() []byte {
buf := bytes.NewBufferString("")
if err := u.Write(buf); err != nil {
panic(err)
}
return buf.Bytes()
}
// DhcpRequest is a simple DHCP request
type DhcpRequest struct {
MAC net.HardwareAddr
}
// NewDhcpRequest constructs a DHCP request
func NewDhcpRequest(MAC net.HardwareAddr) *DhcpRequest {
if len(MAC) != 6 {
panic("MAC address must be 6 bytes")
}
return &DhcpRequest{MAC}
}
// Bytes returns the marshalled DHCP request
func (d *DhcpRequest) Bytes() []byte {
bs := []byte{
0x01, // OP
0x01, // HTYPE
0x06, // HLEN
0x00, // HOPS
0x01, 0x00, 0x00, 0x00, // XID
0x00, 0x00, // SECS
0x80, 0x00, // FLAGS
0x00, 0x00, 0x00, 0x00, // CIADDR
0x00, 0x00, 0x00, 0x00, // YIADDR
0x00, 0x00, 0x00, 0x00, // SIADDR
0x00, 0x00, 0x00, 0x00, // GIADDR
d.MAC[0], d.MAC[1], d.MAC[2], d.MAC[3], d.MAC[4], d.MAC[5],
}
bs = append(bs, make([]byte, 202)...)
bs = append(bs, []byte{
0x63, 0x82, 0x53, 0x63, // Magic cookie
0x35, 0x01, 0x01, // DHCP discover
0xff, // Endmark
}...)
return bs
}
// dhcp queries the IP by DHCP
func (v *Vif) dhcp() (net.IP, error) {
broadcastMAC := []byte{0xff, 0xff, 0xff, 0xff, 0xff, 0xff}
broadcastIP := []byte{0xff, 0xff, 0xff, 0xff}
unknownIP := []byte{0, 0, 0, 0}
dhcpRequest := NewDhcpRequest(v.ClientMAC).Bytes()
ipv4 := NewIpv4(broadcastIP, unknownIP)
udpv4 := NewUdpv4(ipv4, 68, 67, dhcpRequest)
ipv4.setData(udpv4.Bytes())
ethernet := NewEthernetFrame(broadcastMAC, v.ClientMAC, 0x800)
ethernet.setData(ipv4.Bytes())
finished := false
go func() {
for !finished {
if err := v.Write(ethernet.Bytes()); err != nil {
panic(err)
}
time.Sleep(time.Second)
}
}()
for {
response, err := v.Read()
if err != nil {
return nil, err
}
ethernet, err = ParseEthernetFrame(response)
if err != nil {
continue
}
for i, x := range ethernet.Dst {
if i > len(v.ClientMAC) || v.ClientMAC[i] != x {
// intended for someone else
continue
}
}
ipv4, err = ParseIpv4(ethernet.Data)
if err != nil {
// probably not an IPv4 packet
continue
}
udpv4, err = ParseUdpv4(ipv4.Data)
if err != nil {
// probably not a UDPv4 packet
continue
}
if udpv4.Src != 67 || udpv4.Dst != 68 {
// not a DHCP response
continue
}
if len(udpv4.Data) < 243 {
// truncated
continue
}
if udpv4.Data[240] != 53 || udpv4.Data[241] != 1 || udpv4.Data[242] != 2 {
// not a DHCP offer
continue
}
var ip net.IP
ip = udpv4.Data[16:20]
finished = true // will terminate sending goroutine
return ip, nil
}
}