Sending Raw packet with Ethernet header using Go Language - sockets

Question

I am trying to send raw TCP packet with custom Ethernet header through raw socket in Go language. I am trying to reproduce similar code in c language.
package main
import (
"fmt"
"syscall"
)
func main() {
fmt.Println("=============================================================================")
fmt.Println("= Start sending =")
fmt.Println("=============================================================================")
pkt := []byte{
0x6c, 0x62, 0x6d, 0x50, 0xe6, 0xe4, 0x94, 0xde, 0x80, 0xa5, 0xec, 0x79, 0x08, 0x00, 0x45, 0x00,
0x00, 0x3c, 0x47, 0xd9, 0x40, 0x00, 0x40, 0x06, 0xb5, 0x94, 0xc0, 0xa8, 0x34, 0x7b, 0x36, 0xe7,
0x11, 0x44, 0xc3, 0x66, 0x00, 0x50, 0x09, 0x58, 0x6b, 0xeb, 0x00, 0x00, 0x00, 0x00, 0xa0, 0x02,
0x72, 0x10, 0x26, 0x38, 0x00, 0x00, 0x02, 0x04, 0x05, 0xb4, 0x04, 0x02, 0x08, 0x0a, 0x0d, 0x3d,
0x2c, 0x32, 0x00, 0x00, 0x00, 0x00, 0x01, 0x03, 0x03, 0x07,
}
fd, err := syscall.Socket(syscall.AF_PACKET, syscall.SOCK_RAW, syscall.ETH_P_ALL)
if err != nil {
fmt.Println("=============================================================================")
fmt.Println("= Error 1 =")
fmt.Println("=============================================================================")
fmt.Println(err)
}
addr := syscall.SockaddrInet4{
Port: 0,
Addr: [4]byte{127, 0, 0, 1},
}
err = syscall.Bind(fd, &addr)
if err != nil {
fmt.Println("=============================================================================")
fmt.Println("= Error 2 =")
fmt.Println("=============================================================================")
fmt.Println(err)
}
err = syscall.SetLsfPromisc("eth0", true)
if err != nil {
fmt.Println("=============================================================================")
fmt.Println("= Error 3 =")
fmt.Println("=============================================================================")
fmt.Println(err)
}
n, err := syscall.Write(fd, pkt)
if err != nil {
fmt.Println("=============================================================================")
fmt.Println("= Error 4 =")
fmt.Println("=============================================================================")
fmt.Println(err)
fmt.Println(n)
} else {
fmt.Println("=============================================================================")
fmt.Println("= Packet is sent =")
fmt.Println("=============================================================================")
fmt.Println(n)
}
}
However I am getting following error:
=============================================================================
= Start sending =
=============================================================================
=============================================================================
= Error 2 =
=============================================================================
invalid argument
=============================================================================
= Error 4 =
=============================================================================
no such device or address
-1
Please guide me if you have any knowledge.

Answer 1

What you want to accomplish is more complicated.
You cannot use the kernels bind syscall to bind to a raw socket: err = syscall.Bind(fd, &addr)
You want to write ethernet frames to the raw socket. In order to do so you need to assemble the ethernet frame and TCP header yourself. The whole point of using a raw socket on that level is not having the kernel do this for you.
Some working examples in C can be found here. They are probably easy to port to Go

Answer 2

Here is working code of my problem. I will add explanation later.
package main
import (
"fmt"
"net"
"syscall"
)
func main() {
fmt.Println("=============================================================================")
fmt.Println("= Start sending =")
fmt.Println("=============================================================================")
pkt := []byte{
0x6c, 0x62, 0x6d, 0x50, 0xe6, 0xe4, 0x94, 0xde, 0x80, 0xa5, 0xec, 0x79, 0x08, 0x00, 0x45, 0x00,
0x00, 0x3c, 0x4b, 0x72, 0x40, 0x00, 0x40, 0x06, 0x44, 0x7d, 0xc0, 0xa8, 0x34, 0x7b, 0xd8, 0x3a,
0xdd, 0x6e, 0xa6, 0x37, 0x01, 0xbb, 0x32, 0xf3, 0x21, 0xa9, 0x00, 0x00, 0x00, 0x00, 0xa0, 0x02,
0x72, 0x10, 0xae, 0xa5, 0x00, 0x00, 0x02, 0x04, 0x05, 0xb4, 0x04, 0x02, 0x08, 0x0a, 0x15, 0x13,
0x6a, 0xdb, 0x00, 0x00, 0x00, 0x00, 0x01, 0x03, 0x03, 0x07,
}
fd, err := syscall.Socket(syscall.AF_PACKET, syscall.SOCK_RAW, syscall.ETH_P_ALL)
if err != nil {
fmt.Println("=============================================================================")
fmt.Println("= Error 1 =")
fmt.Println("=============================================================================")
fmt.Println(err)
}
if_info, err := net.InterfaceByName("eth0")
if err != nil {
fmt.Println("=============================================================================")
fmt.Println("= Error 2 =")
fmt.Println("=============================================================================")
fmt.Println(err)
}
var haddr [8]byte
copy(haddr[0:7], if_info.HardwareAddr[0:7])
addr := syscall.SockaddrLinklayer{
Protocol: syscall.ETH_P_IP,
Ifindex: if_info.Index,
Halen: uint8(len(if_info.HardwareAddr)),
Addr: haddr,
}
err = syscall.Bind(fd, &addr)
if err != nil {
fmt.Println("=============================================================================")
fmt.Println("= Error 3 =")
fmt.Println("=============================================================================")
fmt.Println(err)
}
err = syscall.SetLsfPromisc("eth0", true)
if err != nil {
fmt.Println("=============================================================================")
fmt.Println("= Error 4 =")
fmt.Println("=============================================================================")
fmt.Println(err)
}
n, err := syscall.Write(fd, pkt)
if err != nil {
fmt.Println("=============================================================================")
fmt.Println("= Error 5 =")
fmt.Println("=============================================================================")
fmt.Println(err)
fmt.Println(n)
} else {
fmt.Println("=============================================================================")
fmt.Println("= Packet is sent =")
fmt.Println("=============================================================================")
fmt.Println(n)
}
err = syscall.SetLsfPromisc("eth0", false)
if err != nil {
fmt.Println("=============================================================================")
fmt.Println("= Error 6 =")
fmt.Println("=============================================================================")
fmt.Println(err)
}
}