zoreide/arp.go

172 lines
4.4 KiB
Go

package main
import (
"bytes"
"encoding/binary"
"fmt"
"log"
"net"
"syscall"
"unsafe"
)
// This subpackage while adapted, is orignally from code from Google's Seesaw
// Github link here: https://github.com/google/seesaw
// see original copyright notice below:
// Copyright 2013 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Author: jsing@google.com (Joel Sing)
// Gratuitous encapsulates a request to send a gratuitous ARP message.
type Gratuitous struct {
IfaceName string
IP net.IP
}
const (
opARPRequest = 1
opARPReply = 2
hwLen = 6
)
var (
ethernetBroadcast = net.HardwareAddr{0xff, 0xff, 0xff, 0xff, 0xff, 0xff}
)
func htons(p uint16) uint16 {
var b [2]byte
binary.BigEndian.PutUint16(b[:], p)
return *(*uint16)(unsafe.Pointer(&b))
}
// arpHeader specifies the header for an ARP message.
type arpHeader struct {
hardwareType uint16
protocolType uint16
hardwareAddressLength uint8
protocolAddressLength uint8
opcode uint16
}
// arpMessage represents an ARP message.
type arpMessage struct {
arpHeader
senderHardwareAddress []byte
senderProtocolAddress []byte
targetHardwareAddress []byte
targetProtocolAddress []byte
}
// bytes returns the wire representation of the ARP message.
func (m *arpMessage) bytes() ([]byte, error) {
buf := new(bytes.Buffer)
if err := binary.Write(buf, binary.BigEndian, m.arpHeader); err != nil {
return nil, fmt.Errorf("binary write failed: %v", err)
}
buf.Write(m.senderHardwareAddress)
buf.Write(m.senderProtocolAddress)
buf.Write(m.targetHardwareAddress)
buf.Write(m.targetProtocolAddress)
return buf.Bytes(), nil
}
// gratuitousARPReply returns an ARP message that contains a gratuitous ARP
// reply from the specified sender.
func gratuitousARPReply(ip net.IP, mac net.HardwareAddr) (*arpMessage, error) {
if ip.To4() == nil {
return nil, fmt.Errorf("%q is not an IPv4 address", ip)
}
if len(mac) != hwLen {
return nil, fmt.Errorf("%q is not an Ethernet MAC address", mac)
}
m := &arpMessage{
arpHeader{
1, // Ethernet
0x0800, // IPv4
hwLen, // 48-bit MAC Address
net.IPv4len, // 32-bit IPv4 Address
opARPReply, // ARP Reply
},
mac,
ip.To4(),
ethernetBroadcast,
net.IPv4bcast,
}
return m, nil
}
// sendARP sends the given ARP message via the specified interface.
func sendARP(iface *net.Interface, m *arpMessage) error {
fd, err := syscall.Socket(syscall.AF_PACKET, syscall.SOCK_DGRAM, int(htons(syscall.ETH_P_ARP)))
if err != nil {
return fmt.Errorf("failed to get raw socket: %v", err)
}
defer syscall.Close(fd)
if err := syscall.BindToDevice(fd, iface.Name); err != nil {
return fmt.Errorf("failed to bind to device: %v", err)
}
ll := syscall.SockaddrLinklayer{
Protocol: htons(syscall.ETH_P_ARP),
Ifindex: iface.Index,
Pkttype: 0, // syscall.PACKET_HOST
Hatype: m.hardwareType,
Halen: m.hardwareAddressLength,
}
target := ethernetBroadcast
if m.opcode == opARPReply {
target = m.targetHardwareAddress
}
// for i := 0; i < len(target); i++ {
// ll.Addr[i] = target[i]
// }
log.Println("Copied ARP: ", copy(ll.Addr[:], target))
b, err := m.bytes()
if err != nil {
return fmt.Errorf("failed to convert ARP message: %v", err)
}
if err := syscall.Bind(fd, &ll); err != nil {
return fmt.Errorf("failed to bind: %v", err)
}
if err := syscall.Sendto(fd, b, 0, &ll); err != nil {
return fmt.Errorf("failed to send: %v", err)
}
return nil
}
// SendGratuitous sends a gratuitous ARP message via the specified interface.
func SendGratuitous(arp *Gratuitous) error { //, out *int) error {
iface, err := net.InterfaceByName(arp.IfaceName)
if err != nil {
return fmt.Errorf("failed to get interface %q: %v", arp.IfaceName, err)
}
log.Printf("Sending gratuitous ARP for %s (%s) via %s\n", arp.IP, iface.HardwareAddr, iface.Name)
m, err := gratuitousARPReply(arp.IP, iface.HardwareAddr)
if err != nil {
return err
}
return sendARP(iface, m)
}