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Add support for AF_UNIX SOCK_DGRAM
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Unfortunately these aren't supported by libuv directly, so we need to
implement our own separate system. It doesn't need to be particularly
scalable as the expected use-case is to send and receive ethernet frames.

The server will listen on a Unix domain socket and receive connected
SOCK_DGRAM sockets which will have ethernet frames on them.

Signed-off-by: David Scott <[email protected]>
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djs55 committed Oct 9, 2022
1 parent 44428dd commit 6286c5d
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Showing 36 changed files with 2,270 additions and 787 deletions.
41 changes: 41 additions & 0 deletions go/cmd/vmnet-example/main.go
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package main

import (
"context"
"flag"
"fmt"
"log"
"os"

"github.com/google/uuid"
"github.com/moby/vpnkit/go/pkg/vmnet"
)

var path string

func main() {
flag.StringVar(&path, "path", "", "path to vmnet socket")
flag.Parse()
if path == "" {
fmt.Fprintf(os.Stderr, "Please supply a --path argument\n")
}
vm, err := vmnet.Connect(context.Background(), vmnet.Config{
Path: path,
})
if err != nil {
log.Fatal(err)
}
defer vm.Close()
log.Println("connected to vmnet service")
u, err := uuid.NewRandom()
if err != nil {
log.Fatal(err)
}
vif, err := vm.ConnectVif(u)
if err != nil {
log.Fatal(err)
}
defer vif.Close()
log.Printf("VIF has IP %s", vif.IP)
log.Printf("SOCK_DGRAM fd: %d", vif.Ethernet.Fd)
}
50 changes: 50 additions & 0 deletions go/pkg/vmnet/datagram.go
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package vmnet

/*
// FIXME: Needed because we call C.send. Perhaps we could use syscall instead?
#include <stdlib.h>
#include <sys/socket.h>
*/
import "C"

import (
"syscall"

"github.com/pkg/errors"
)

// Datagram sends and receives ethernet frames via send/recv over a SOCK_DGRAM fd.
type Datagram struct {
Fd int // Underlying SOCK_DGRAM file descriptor.
pcap *PcapWriter
}

func (e Datagram) Recv(buf []byte) (int, error) {
num, _, err := syscall.Recvfrom(e.Fd, buf, 0)
if e.pcap != nil {
if err := e.pcap.Write(buf[0:num]); err != nil {
return 0, errors.Wrap(err, "writing to pcap")
}
}
return num, err
}

func (e Datagram) Send(packet []byte) (int, error) {
if e.pcap != nil {
if err := e.pcap.Write(packet); err != nil {
return 0, errors.Wrap(err, "writing to pcap")
}
}
result, err := C.send(C.int(e.Fd), C.CBytes(packet), C.size_t(len(packet)), 0)
if result == -1 {
return 0, err
}
return len(packet), nil
}

func (e Datagram) Close() error {
return syscall.Close(e.Fd)
}

var _ sendReceiver = Datagram{}
114 changes: 114 additions & 0 deletions go/pkg/vmnet/dhcp.go
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package vmnet

import (
"net"
"time"
)

// dhcp queries the IP by DHCP
func dhcpRequest(packet sendReceiver, clientMAC net.HardwareAddr) (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(clientMAC).Bytes()
ipv4 := NewIpv4(broadcastIP, unknownIP)

udpv4 := NewUdpv4(ipv4, 68, 67, dhcpRequest)
ipv4.setData(udpv4.Bytes())

ethernet := NewEthernetFrame(broadcastMAC, clientMAC, 0x800)
ethernet.setData(ipv4.Bytes())
finished := false
go func() {
for !finished {
if _, err := packet.Send(ethernet.Bytes()); err != nil {
panic(err)
}
time.Sleep(time.Second)
}
}()

buf := make([]byte, 1500)
for {
n, err := packet.Recv(buf)
if err != nil {
return nil, err
}
response := buf[0:n]
ethernet, err = ParseEthernetFrame(response)
if err != nil {
continue
}
for i, x := range ethernet.Dst {
if i > len(clientMAC) || 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
}
}

// 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
}
66 changes: 66 additions & 0 deletions go/pkg/vmnet/ethernet.go
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package vmnet

import (
"bytes"
"encoding/binary"
"io"
"net"

"github.com/pkg/errors"
)

// 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()
}
54 changes: 54 additions & 0 deletions go/pkg/vmnet/framing.go
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package vmnet

import (
"encoding/binary"
"io"
)

// Messages sent to vpnkit can either be
// - fixed-size, no length prefix
// - variable-length, with a length prefix

// fixedSizeSendReceiver sends and receives fixed-size control messages with no length prefix.
type fixedSizeSendReceiver struct {
rw io.ReadWriter
}

var _ sendReceiver = fixedSizeSendReceiver{}

func (f fixedSizeSendReceiver) Recv(buf []byte) (int, error) {
return io.ReadFull(f.rw, buf)
}

func (f fixedSizeSendReceiver) Send(buf []byte) (int, error) {
return f.rw.Write(buf)
}

// lengthPrefixer sends and receives variable-length control messages with a length prefix.
type lengthPrefixer struct {
rw io.ReadWriter
}

var _ sendReceiver = lengthPrefixer{}

func (e lengthPrefixer) Recv(buf []byte) (int, error) {
var len uint16
if err := binary.Read(e.rw, binary.LittleEndian, &len); err != nil {
return 0, err
}
if err := binary.Read(e.rw, binary.LittleEndian, &buf); err != nil {
return 0, err
}
return int(len), nil
}

func (e lengthPrefixer) Send(packet []byte) (int, error) {
len := uint16(len(packet))
if err := binary.Write(e.rw, binary.LittleEndian, len); err != nil {
return 0, err
}
if err := binary.Write(e.rw, binary.LittleEndian, packet); err != nil {
return 0, err
}
return int(len), nil
}
68 changes: 68 additions & 0 deletions go/pkg/vmnet/ipv4.go
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package vmnet

import (
"net"

"github.com/pkg/errors"
)

// 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...)
}
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