packetselector.py

# MIT License

# Copyright (c) 2017 Balazs Bucsay

# 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 sys

if "packetselector.py" in sys.argv[0]:
	print("[-] Instead of poking around just try: python xfltreat.py --help")
	sys.exit(-1)

# This is the engine of the whole communication. Every packet that arrives to 
# the tunnel will be carefully selected. In case the destination IP matches, it
# will be redirected (written) to the appropriate client pipe.

import threading
import os
import select
import struct
import socket

#local files
import common
from client import Client

class PacketSelector(threading.Thread):
	clients = None

	def __init__(self, tunnel):
		threading.Thread.__init__(self)
		self.timeout = 1.0 # seems to be a good value for timeout
		self.clients = []
		self.tunnel = tunnel
		self._stop = False
		self.os_type = common.get_os_type()

		if self.os_type == common.OS_WINDOWS:
			self.run_ps_mainloop = self.run_windows
		else:
			self.run_ps_mainloop = self.run_unix

	# return client list
	def get_clients(self):

		return self.clients

	# add new client to the client list
	def add_client(self, client):
		self.clients.append(client)

		return

	# This function is called when a client object has to be replaced.
	# That could happen when the client connection was reset, or there is a
	# duplicated config with the same private IP.
	def replace_client(self, old_client, new_client):
		if old_client in self.clients:
			self.clients.remove(old_client)
			self.clients.append(new_client)
			try:
				old_client.get_pipe_w_fd().close()
			except:
				pass
			try:
				old_client.get_pipe_r_fd().close()
			except:
				pass
			try:
				socket.close(old_client.get_socket())
			except:
				pass

	# removing client from the client list
	def delete_client(self, client):
		if client in self.clients:

			if self.os_type == common.OS_WINDOWS:
				import win32file

				try:
					win32file.CloseHandle(client.get_pipe_r())
					win32file.CloseHandle(client.get_pipe_w())
				except Exception as e:
					common.internal_print("Remove authenticated client: CloseHandle exception: {0}".format(e), -1)
			else:
				try:
					client.get_pipe_r_fd().close()
					client.get_pipe_w_fd().close()
				except Exception as e:
					common.internal_print("Remove authenticated client: os.close exception: {0}".format(e), -1)

			client.call_stopfp()
			self.clients.remove(client)

		return

	# This function should run from the point when the framework was started.
	# It runs as an infinite loop to read the packets off the tunnel.
	# When an IPv4 packet was found that will be selected and checked whether
	# it addresses a client in the client list. If a client was found, then the
	# packet will be written on that pipe.
	def run(self):
		return self.run_ps_mainloop()


	def run_unix(self):
		rlist = [self.tunnel]
		wlist = []
		xlist = []

		while not self._stop:
			try:
				readable, writable, exceptional = select.select(rlist, wlist, xlist, self.timeout)
			except select.error as e:
				print(e)
				break

			for s in readable:
				# is there anything on the tunnel interface?
				if s is self.tunnel:
					# yes there is, read the packet or packets off the tunnel
					message = os.read(self.tunnel, 4096)
					if self.os_type == common.OS_MACOSX:
						message = message[4:]
					while True:
						# dumb check, but seems to be working. The packet has 
						# to be longer than 4 and it must be IPv4
						if (len(message) < 4) or (message[0:1] != "\x45"): #Only care about IPv4
							break
						packetlen = struct.unpack(">H", message[2:4])[0]
						if packetlen == 0:
							break
						# is the rest less than the packet length?
						if packetlen > len(message):
							# in case it is less, we need to read more
							message += os.read(self.tunnel, 4096)
						readytogo = message[0:packetlen]
						message = message[packetlen:]
						# looking for client
						for c in self.clients:
							if c.get_private_ip_addr() == readytogo[16:20]:
								# client found, writing packet on client's pipe
								try:
									os.write(c.get_pipe_w(), readytogo)
									# flushing, no buffering please
									c.get_pipe_w_fd().flush()
								except:
									# it can break if there is a race condition
									# the client was found above but in the
									# same time the client left and the pipe
									# got closed. Broken pipe would be raised
									pass

		return


	# some ideas were taken from: https://github.com/boytm/minivtun-win/
	def run_windows(self):
		import win32file
		import win32event
		import pywintypes
		import winerror
		import win32api

		# creating events, overlapped structures and a buffer for reading and writing
		hEvent_read = win32event.CreateEvent(None, 0, 0, None)
		overlapped_read = pywintypes.OVERLAPPED()
		overlapped_read.hEvent = hEvent_read
		overlapped_write = pywintypes.OVERLAPPED()
		message = win32file.AllocateReadBuffer(4096)

		while not self._stop:
			try:
				# Overlapped/async read, it either blocks or returns pending
				hr, _ = win32file.ReadFile(self.tunnel, message, overlapped_read)
				if (hr == winerror.ERROR_IO_PENDING):
					# when the event gets signalled or timeout happens it will return
					rc = win32event.WaitForSingleObject(hEvent_read, int(self.timeout*1000))
					if rc == winerror.WAIT_TIMEOUT:
						# timed out, just rerun read
						continue

					if rc == win32event.WAIT_OBJECT_0:
						# read happened, packet is in "message"
						if (overlapped_read.InternalHigh < 4) or (message[0:1] != "\x45"): #Only care about IPv4
							# too small which should not happen or not IPv4, so we just drop it.
							continue

						# reading out the packet from the buffer and discarding the rest
						readytogo = message[0:overlapped_read.InternalHigh]

				# looking for client
				for c in self.clients:
					if c.get_private_ip_addr() == readytogo[16:20]:
						# client found, writing packet on client's pipe
						# ignoring outcome, it is async so it will happen when it will happen ;)
						win32file.WriteFile(c.get_pipe_w(), readytogo, overlapped_write)

			except win32api.error as e:
				if e.args[0] == 995:
					common.internal_print("Interface disappered, exiting PS thread: {0}".format(e), -1)
					self.stop()
					continue
				if e.args[0] == 1453:
					common.internal_print("OS Internal error: {0}".format(e), -1)
					self.stop()
					continue

				common.internal_print("PS Exception: {0}".format(e), -1)

		return


	# stop the so called infinite loop
	def stop(self):
		self._stop = True

		return