frag_dropnew.py revision 1.4 
1#!/usr/local/bin/python2.7
2# old fragment completely overlaps new one
3
4#      |------------|
5#          |XXXX|
6# |----|
7
8# If the current fragment is completely overlapped by existing ones,
9# drop the newer fragment.
10#                 if (precut >= frent->fe_len)
11#                         goto bad_fragment;
12# 'Nearer' traffic wins.
13
14import os
15from addr import *
16from scapy.all import *
17
18dstaddr=sys.argv[1]
19pid=os.getpid() & 0xffff
20payload="ABCDEFGHIJKLOMNOQRSTUVWX"
21dummy="01234567"
22packet=IP(src=SRC_OUT, dst=dstaddr)/ICMP(id=pid)/payload
23frag0=str(packet)[20:28]
24frag1=dummy
25frag2=str(packet)[28:52]
26pkt0=IP(src=SRC_OUT, dst=dstaddr, proto=1, id=pid, frag=0, flags='MF')/frag0
27pkt1=IP(src=SRC_OUT, dst=dstaddr, proto=1, id=pid, frag=2, flags='MF')/frag1
28pkt2=IP(src=SRC_OUT, dst=dstaddr, proto=1, id=pid, frag=1)/frag2
29eth=[]
30eth.append(Ether(src=SRC_MAC, dst=PF_MAC)/pkt2)
31eth.append(Ether(src=SRC_MAC, dst=PF_MAC)/pkt1)
32eth.append(Ether(src=SRC_MAC, dst=PF_MAC)/pkt0)
33
34if os.fork() == 0:
35	time.sleep(1)
36	sendp(eth, iface=SRC_IF)
37	os._exit(0)
38
39ans=sniff(iface=SRC_IF, timeout=3, filter=
40    "ip and src "+dstaddr+" and dst "+SRC_OUT+" and icmp")
41a=ans[0]
42if a and a.type == ETH_P_IP and \
43    a.payload.proto == 1 and \
44    a.payload.frag == 0 and a.payload.flags == 0 and \
45    icmptypes[a.payload.payload.type] == 'echo-reply':
46	id=a.payload.payload.id
47	print "id=%#x" % (id)
48	if id != pid:
49		print "WRONG ECHO REPLY ID"
50		exit(2)
51	load=a.payload.payload.payload.load
52	print "payload=%s" % (load)
53	if load == payload:
54		exit(0)
55	print "PAYLOAD!=%s" % (payload)
56	exit(1)
57print "NO ECHO REPLY"
58exit(2)
59