punchd/raw_socket.nim

import asyncdispatch
from nativesockets import
  AF_INET,
  IPPROTO_IP,
  IPPROTO_TCP,
  SOCK_RAW,
  bindAddr,
  htons,
  setSockOptInt
from posix import setsockopt, SockAddr, SockLen, SocketHandle
import network_interface

type
  RawSocketError* = object of CatchableError
  
  Sockaddr_ll {.importc: "struct sockaddr_ll", pure, final,
                header: "<linux/if_packet.h>".} = object
    sll_family: cushort        # Always AF_PACKET
    sll_protocol: cushort      # Physical-layer protocol
    sll_ifindex: cint          # Interface number
    sll_hatype: cushort        # ARP hardware type
    sll_pkttype: cuchar        # Packet type
    sll_halen: cuchar          # Length of address
    sll_addr: array[8, cuchar] # Physical-layer address

  Packet_mreq {.importc: "struct packet_mreq", pure, final,
                header: "<linux/if_packet.h>".} = object
    mr_ifindex: cint
    mr_type: cushort
    mr_alen: cushort
    mr_address: array[8, cuchar]

var
  AF_PACKET {.importc: "AF_PACKET", header: "<sys/socket.h>".}: cushort
  SOL_PACKET {.importc: "SOL_PACKET", header: "<sys/socket.h>".}: cushort
  ETH_P_ALL {.importc: "ETH_P_ALL", header: "<linux/if_ether.h>".}: cushort
  IP_HDRINCL {.importc: "IP_HDRINCL", header: "<netinet/in.h>".}: cint
  PACKET_ADD_MEMBERSHIP {.importc: "PACKET_ADD_MEMBERSHIP", header: "<linux/if_packet.h>".}: cushort
  PACKET_MR_PROMISC {.importc: "PACKET_MR_PROMISC", header: "<linux/if_packet.h>".}: cushort

proc setupEthernetCapturingSocket*(iface: NetworkInterface): AsyncFD =
  # Create a raw packet socket. For accessing outgoing packets we need to use
  # ETH_P_ALL which is needed in network byte order, see packet(7) man page.
  result = createAsyncNativeSocket(AF_PACKET.cint,
                                   SOCK_RAW.cint,
                                   htons(ETH_P_ALL).cint)

  # Limit capturing of packets to the desired network interface, see
  # netdevice(7) man page
  echo "interface: ", iface.name, ", index: ", iface.index
  var sa = Sockaddr_ll(sll_family: AF_PACKET,
                       sll_protocol: htons(ETH_P_ALL),
                       sll_ifindex: iface.index)
  if bindAddr(result.SocketHandle,
              cast[ptr SockAddr](addr sa),
              sizeof(Sockaddr_ll).SockLen) != 0:
    raise newException(RawSocketError, "cannot bind to interface")
  
  # Enable promiscuous mode, see netdevice(7) man page
  var req = Packet_mreq(mr_ifindex: iface.index, mr_type: PACKET_MR_PROMISC)
  if setsockopt(result.SocketHandle,
                SOL_PACKET.cint,
                PACKET_ADD_MEMBERSHIP.cint,
                addr req,
                sizeof(req).SockLen) != 0:
    raise newException(RawSocketError, "cannot enable promiscuous mode")

proc setupTcpInjectingSocket*(): AsyncFD =
  # FIXME: would bindAddr be beneficial?
  result = createAsyncNativeSocket(AF_INET.cint, SOCK_RAW.cint,
                                   IPPROTO_TCP.cint)

  # Tell the kernel to not generate an IP header, as we generate it ourselves,
  # see raw(7) man page.
  setSockOptInt(result.SocketHandle, IPPROTO_IP.int, IP_HDRINCL, 1)