netdev - Re: [PATCH] netfilter: nf_conntrack: reserve two bytes for nf_ct

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Date:	Thu, 27 Mar 2014 16:50:33 +0100
From:	Florian Westphal <fw@...len.de>
To:	Andrey Vagin <avagin@...nvz.org>
Cc:	linux-kernel@...r.kernel.org, netfilter-devel@...r.kernel.org,
	netfilter@...r.kernel.org, coreteam@...filter.org,
	netdev@...r.kernel.org, vvs@...allels.com,
	Pablo Neira Ayuso <pablo@...filter.org>,
	Patrick McHardy <kaber@...sh.net>,
	Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH] netfilter: nf_conntrack: reserve two bytes for
 nf_ct_ext->len

Andrey Vagin <avagin@...nvz.org> wrote:
> "len" contains sizeof(nf_ct_ext) and size of extensions. In a worst
> case it can contain all extensions. Bellow you can find sizes for all
> types of extensions. Their sum is definitely bigger than 256.
> 
> nf_ct_ext_types[0]->len = 24
> nf_ct_ext_types[1]->len = 32
> nf_ct_ext_types[2]->len = 24
> nf_ct_ext_types[3]->len = 32
> nf_ct_ext_types[4]->len = 152

Guess its  the timer in the ecache extension (with LOCKDEP on probably).

I'll submit a patch to get rid of that shortly.

I think your patch is fine because the 'no timer
in ecache extension' change is quite large, needs review/stress testing
etc and is inapropriate for stable tree anyway.

> I have seen "len" up to 280 and my host has crashes w/o this patch.

ecache is 24 bytes without that timer, should be < 256 in total for
all extensions.

I think BUILD_BUG_ON test would be nice.
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