scanner.py

#!/usr/bin/python
__author__ = 'kalcho'

import socket
import os
import struct
from ctypes import *
import threading
import time
from netaddr import IPNetwork, IPAddress

# host to listen on
host = socket.gethostname()

# subnet to target
subnet = '192.168.0.0/24'

# magic we'll check ICMP responses for
magic_message = 'PYTHONRULES!'

# this sprays out the UDP datagrams
def udp_sender(subnet, magic_message):
    time.sleep(5)
    sender = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

    for ip in IPNetwork(subnet):
        try:
            sender.sendto(magic_message, ("%s" % ip, 65212))
        except:
            pass

# our IP header
class IP(Structure):
    _fields_ = [
        ("ihl",             c_ubyte, 4),
        ("version",         c_ubyte, 4),
        ("tos",             c_ubyte),
        ("len",             c_ushort),
        ("id",              c_ushort),
        ("offset",          c_ushort),
        ("ttl",             c_ubyte),
        ("protocol_num",    c_ubyte),
        ("sum",             c_ushort),
        ("src",             c_ulong),
        ("dst",             c_ulong)
    ]

    def __new__(self, socket_buffer=None):
        return self.from_buffer_copy(socket_buffer)

    def __init__(self, socket_buffer=None):
        # map protocol constants to their names
        self.protocol_map = {1:"ICMP", 6:"TCP", 17:"UDP"}

        # human readable IP addresses
        self.src_address = socket.inet_ntoa(struct.pack("<L", self.src))
        self.dst_address = socket.inet_ntoa(struct.pack("<L",self.dst))

        # human readable protocol
        try:
            self.protocol = self.protocol_map[self.protocol_num]
        except:
            self.protocol = str(self.protocol_num)


class ICMP(Structure):

    _fields_ = [
        ("type",            c_ubyte),
        ("code",            c_ubyte),
        ("checksum",        c_ushort),
        ("unused",          c_ushort),
        ("next_hop_mtu",    c_ushort),
    ]

    def __new__(self, socket_buffer):
        return self.from_buffer_copy(socket_buffer)

    def __init__(self, socket_buffer):
        pass

# create a raw socket and bind it to the public interface
if os.name == "nt":
    socket_protocol = socket.IPPROTO_IP
else:
    socket_protocol = socket.IPPROTO_ICMP

sniffer = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket_protocol)

sniffer.bind((socket.gethostbyname(host), 0))

# we want the IP headers included in the capture
sniffer.setsockopt(socket.IPPROTO_IP, socket.IP_HDRINCL, 1)

# if we're using Windows, we need to send an IOCTL
# to set up promiscuous mode
if os.name == "nt":
    sniffer.ioctl(socket.SIO_RCVALL, socket.RCVALL_ON)

# start sending packets
t = threading.Thread(target=udp_sender, args=(subnet, magic_message))
t.start()

# read in a single packet
#print sniffer.recvfrom(65565)

# if we're using Windows, turn off promiscuous mode
#if os.name == "nt":
#    sniffer.ioctl(socket.SIO_RCVALL, socket.RCVALL_OFF)

try:
    while True:
        
        # read in a single packet
        raw_buffer = sniffer.recvfrom(65565)[0]
        
        # create an IP header from the first 20 bytes of the buffer
        ip_header = IP(raw_buffer[0:20])

        # print out the protocol that was detected and the hosts
        #print "Protocol: %s %s -> %s" % (ip_header.protocol, \
        #    ip_header.src_address, ip_header.dst_address)
        
        # if it's ICMP, we want it
        if ip_header.protocol == "ICMP":

            # calculate where our ICMP packet starts
            offset = ip_header.ihl * 4
            buf = raw_buffer[offset:offset + sizeof(ICMP)]

            # create our ICMP structure
            icmp_header = ICMP(buf)

            #print "ICMP -> Type: %d Code: %d" % (icmp_header.type, icmp_header.code)

            # now check for the TYPE 3 (Destination Unreachable) and
            # CODE 3 (Port Unreachable) which indicates
            # a host is up but no port available to talk to
            if icmp_header.code == 3 and icmp_header.type == 3:

                # check to make sure we are receiving the response
                # that lands in our target subnet
                if IPAddress(ip_header.src_address) in IPNetwork(subnet):
                    
                    # make sure response has our magic message
                    if raw_buffer[len(raw_buffer)-len(magic_message):] == magic_message:
                        print "Host Up: %s" % ip_header.src_address

# handle CTRL-C
except KeyboardInterrupt:
    
    # if we're using Windows, turn off promiscuous mode
    if os.name == "nt":
        sniffer.ioctl(socket.SIO_RCVALL, socket.RCVALL_OFF)