#
# 5D4A LAB - emdel - 25/08/2011
#

import logging

l=logging.getLogger("scapy.runtime")
l.setLevel(49)

import os,sys,nfqueue,socket
from scapy.all import *

conf.verbose = 0
conf.L3socket = L3RawSocket

def send_echo_reply(pkt):
		ip = IP()
		icmp = ICMP()
		ip.src = pkt[IP].dst 
		ip.dst = pkt[IP].src
		icmp.type = 0
		icmp.code = 0
		icmp.id = pkt[ICMP].id
		icmp.seq = pkt[ICMP].seq
		print "Sending back an echo reply to %s" % ip.dst
		data = pkt[ICMP].payload
		send(ip/icmp/data, verbose=0)


def process(i, payload):
	data = payload.get_data()
	pkt = IP(data)
	proto = pkt.proto

	# Dropping the packet
	payload.set_verdict(nfqueue.NF_DROP)
	
	# Check if it is a ICMP packet
	if proto is 0x01:
			print "It's an ICMP packet"
			# Idea: intercept an echo request and immediately send back an echo reply packet
			if pkt[ICMP].type is 8:
				print "It's an ICMP echo request packet"
				send_echo_reply(pkt)
			else:
				pass
			
	else:
		print "Protocol not handled!!"
		pass


def main():
	q = nfqueue.queue()
	q.open()
	q.bind(socket.AF_INET)
	q.set_callback(process)
	q.create_queue(0)

	try:
		q.try_run()
	except KeyboardInterrupt:
		print "Exiting..."
		q.unbind(socket.AF_INET)
		q.close()
		sys.exit(1)

main()