1#!/usr/local/bin/python2.7
2# do a tcp handshake for the client and server connection
3
4import os
5import sys
6import threading
7from addr import *
8from scapy.all import *
9
10client=os.getpid() & 0xffff
11relay=int(sys.argv[2])
12server=int(sys.argv[1])
13
14class Sniff1(threading.Thread):
15	filter = None
16	captured = None
17	packet = None
18	def __init__(self):
19		# clear packets buffered by scapy bpf
20		sniff(iface=LOCAL_IF, timeout=1)
21		super(Sniff1, self).__init__()
22	def run(self):
23		self.captured = sniff(iface=LOCAL_IF, filter=self.filter,
24		    count=1, timeout=5)
25		if self.captured:
26			self.packet = self.captured[0]
27
28ip=IP(src=FAKE_NET_ADDR, dst=REMOTE_ADDR)
29
30print "Send SYN packet, receive SYN+ACK"
31syn=TCP(sport=client, dport=relay, seq=0, flags='S', window=(2**16)-1)
32synack=sr1(ip/syn, iface=LOCAL_IF, timeout=5)
33
34if synack is None:
35	print "ERROR: No matching SYN+ACK packet received"
36	exit(1)
37
38print "Expect spliced SYN"
39sniffer = Sniff1();
40sniffer.filter = "src %s and dst %s and tcp port %u " \
41    "and tcp[tcpflags] = tcp-syn" % (ip.dst, ip.src, server)
42sniffer.start()
43time.sleep(1)
44
45print "Send ACK packet to finish handshake"
46ack=TCP(sport=synack.dport, dport=synack.sport,
47    seq=1, ack=synack.seq+1,  flags='A')
48send(ip/ack, iface=LOCAL_IF)
49
50sniffer.join(timeout=7)
51spliced_syn = sniffer.packet
52
53if spliced_syn is None:
54	print "ERROR: No spliced SYN packet received"
55	exit(1)
56
57print "Send spliced SYN+ACK packet to finish handshake"
58spliced_synack=TCP(sport=spliced_syn.dport, dport=spliced_syn.sport,
59    seq=0, ack=spliced_syn.seq+1, flags='SA')
60spliced_ack=sr1(ip/spliced_synack, iface=LOCAL_IF)
61
62if spliced_ack is None:
63	print "ERROR: No spliced ACK packet received"
64	exit(1)
65if spliced_ack.seq != spliced_syn.seq+1:
66	print "ERROR: Expected seq %d, got %d in spliced ack" % \
67	    (spliced_syn.seq+1, spliced_ack.seq)
68	exit(1)
69if spliced_ack.ack != 1:
70	print "ERROR: Expected ack %d, got %d in spliced ack" % \
71	    (1, spliced_ack.ack)
72	exit(1)
73if spliced_ack.len-20-20 != 0:
74	print "ERROR: Expected len %d, got %d in spliced ack" % \
75	    (0, spliced_ack.len-20-20)
76	exit(1)
77
78time.sleep(1)
79
80print "Kill connections with RST"
81spliced_rst=TCP(sport=spliced_ack.dport, dport=spliced_ack.sport,
82    seq=1, ack=spliced_ack.seq, flags='RA')
83send(ip/spliced_rst, iface=LOCAL_IF)
84rst=TCP(sport=synack.dport, dport=synack.sport,
85    seq=1, ack=synack.seq+1, flags='RA')
86send(ip/rst, iface=LOCAL_IF)
87
88exit(0)
89