#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# routeradvert-scan.py: Scan for rogue IPv6 router advertisements.
#
# Copyright © 2010 Anders Kaseorg <andersk@mit.edu>
#
# Permission is hereby granted, free of charge, to any person
# obtaining a copy of this software and associated documentation files
# (the “Software”), to deal in the Software without restriction,
# including without limitation the rights to use, copy, modify, merge,
# publish, distribute, sublicense, and/or sell copies of the Software,
# and to permit persons to whom the Software is furnished to do so,
# subject to the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.

import errno
import math
import os
import re
import signal
import socket
import subprocess
import sys
import time

# configuration
interface = 'eth1'
timeout = 30
zclass = 'andersk-auto'
zinstance = '6to4'
zsig = '%s on %s' % (sys.argv[0], socket.gethostname())
# end configuration

mac_re = re.compile(r'^(?:[0-9a-fA-F]{2}:){5}[0-9a-fA-F]{2}$')

seen_macs = {}

def msg(m):
    os.spawnlp(os.P_WAIT, 'zwrite', 'zwrite', '-q', '-d', '-c', zclass, '-i', zinstance, '-s', zsig, '-m', m)

def check_gone():
    now = time.time()
    next = None
    for (mac, t) in seen_macs.items():
        if t < now:
            del seen_macs[mac]
            msg('Gone 6to4 router: %s\nCurrent 6to4 routers: %s' % (mac, seen_macs.keys()))
        elif next is None or next > t:
            next = t
    if next is None:
        signal.alarm(0)
    else:
        signal.alarm(int(math.ceil(next - now)))

msg('Starting %s' % sys.argv[0])

signal.signal(signal.SIGALRM, lambda signum, frame: check_gone())

p = subprocess.Popen(['tcpdump', '-elnp', '-i', interface, 'icmp6 and (ip6[40] = 134)'], stdout=subprocess.PIPE)
while True:
    check_gone()
    while True:
        try:
            line = p.stdout.readline()
        except IOError, (e, s):
            if e == errno.EINTR:
                continue
        break
    signal.alarm(0)
    if line == '':
        break
    words = line.split()
    if len(words) >= 2 and mac_re.match(words[1]):
        mac = words[1]
        t = time.time() + timeout
        if mac in seen_macs:
            seen_macs[mac] = t
        else:
            seen_macs[mac] = t
            msg('New 6to4 router: %s\n%s\nCurrent 6to4 routers: %s' % (mac, line.rstrip('\n'), seen_macs.keys()))
    else:
        print >>sys.stderr, 'Unrecognized line: ', line.rstrip('\n')