Evil bug in netfilter/kernel 2.4.x?

Evil bug in netfilter/kernel 2.4.x?

[jpiszcz]

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?

Please CC me as I am not on the list.

Re: Evil bug in netfilter/kernel 2.4.x?

[Gianni Tedesco]

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On Mon, 2003-02-10 at 22:32, jpiszcz wrote:
> However, when I run tcpdump, I can clearly see these are not getting 
> dropped or logged by the kernel.

Could your problem actually be a testing flaw? tcpdump sees firewalled
packets since it works at packet level, below the IP stack.

-- 
// Gianni Tedesco (gianni at scaramanga dot co dot uk)
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Re: Evil bug in netfilter/kernel 2.4.x?

[jpiszcz]

Other packets are shown as dropped by tcpdump, apparently others said 
this is not a bug.
Also tried to log them etc, so either way was unsuccessful.

Gianni Tedesco wrote:

>On Mon, 2003-02-10 at 22:32, jpiszcz wrote:
>  
>
>>However, when I run tcpdump, I can clearly see these are not getting 
>>dropped or logged by the kernel.
>>    
>>
>
>Could your problem actually be a testing flaw? tcpdump sees firewalled
>packets since it works at packet level, below the IP stack.
>
>  
>