From mboxrd@z Thu Jan  1 00:00:00 1970
From: jpiszcz <jpiszcz@lucidpixels.com>
Subject: Evil bug in netfilter/kernel 2.4.x?
Date: Mon, 10 Feb 2003 17:28:16 -0500
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To: netfilter@lists.netfilter.org

http://iptables-tutorial.frozentux.net/iptables-tutorial.html
"As a secondary note, if you use connection tracking you will not see 
any fragmented packets, since they are dealt with before hitting any 
chain or table in iptables."

PROBLEM:

root@p300:/etc/rc.d# iptables -t filter -I INPUT -f -j LOG --log-level 3 
--log-prefix "FRAG: "
root@p300:/etc/rc.d# iptables -I INPUT -f -j LOG --log-level 3 
--log-prefix "FRAG: "
root@p300:/etc/rc.d# iptables -I INPUT -f -j LOG --log-level 3 
--log-prefix "FRAG: "
root@p300:/etc/rc.d# iptables -I INPUT -f -j DROP

I've tried all of these, each one by itself.

However, when I run tcpdump, I can clearly see these are not getting 
dropped or logged by the kernel.

I like conn_track for DCC/FTP connections, however, to get logging & 
dropping of fragmented packets working properly, I must recompile 
without the conn_tracker's?

Wouldn't this be considered as a bug?  Someone could be 
pounding/scanning you with fragmented packets, and you would never see 
it, as many people run the DCC and/or FTP connection trackers!

box1# nmap -sS -P0 -f -p 1-65535 box2.com

17:11:52.659286 box1.com > box2.com: (frag 2729:4@16)
17:11:52.661416 box1.com > box2.com: (frag 986:4@16)
17:11:52.663400 box1.com > box2.com: (frag 61814:4@16)
17:11:52.665398 box1.com > box2.com: (frag 30216:4@16)
17:11:52.667401 box1.com > box2.com: (frag 4100:4@16)
17:11:52.669392 box1.com > box2.com: (frag 61387:4@16)

947 packets received by filter
0 packets dropped by kernel

Is it possible in anyway to log/drop/match fragmented packets with 
connection tracking turned on?