netdev - Re: [PATCH RFC] ipv6: use stronger hash for reassembly queue hash table

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Date:	Fri, 08 Mar 2013 07:23:39 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	netdev@...r.kernel.org, yoshfuji@...ux-ipv6.org
Subject: Re: [PATCH RFC] ipv6: use stronger hash for reassembly queue hash
 table

On Fri, 2013-03-08 at 16:08 +0100, Hannes Frederic Sowa wrote:
> On Fri, Mar 08, 2013 at 06:53:06AM -0800, Eric Dumazet wrote:
> > No matter how you hash, a hacker can easily fill your defrag unit with
> > not complete datagrams, so what's the point ?
> 
> I want to harden reassembly logic against all fragments being put in
> the same hash bucket because of malicious traffic and thus creating
> long list traversals in the fragment queue hash table.

Note that the long traversal was a real issue with TCP (thats why I
introduced ipv6_addr_jhash()), as a single ehash slot could contains
thousand of sockets.

But with fragments, we should just limit the depth of any particular
slot, and drop above a particular threshold.

reassembly is a best effort mechanism, better make sure it doesnt use
all our cpu cycles.


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