netdev - Re: [PATCH for 2.6.33] conntrack: restrict runtime hashsize modifications

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Date:	Thu, 04 Feb 2010 17:18:50 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	Alexey Dobriyan <adobriyan@...il.com>
CC:	davem@...emloft.net, jonathan@...masters.org,
	eric.dumazet@...il.com, netdev@...r.kernel.org,
	netfilter-devel@...r.kernel.org
Subject: Re: [PATCH for 2.6.33] conntrack: restrict runtime hashsize modifications

Alexey Dobriyan wrote:
> Jon Masters correctly points out that conntrack hash sizes
> (nf_conntrack_htable_size) are global (not per-netns) and
> modifiable at runtime via /sys/module/nf_conntrack/hashsize .
> 
> Steps to reproduce:
> 	clone(CLONE_NEWNET)
> 	[grow /sys/module/nf_conntrack/hashsize]
> 	exit()
> 
> At netns exit we are going to scan random memory for conntracks to be killed.
> 
> Apparently there is a code which deals with hashtable resize for
> init_net (and it was there befode netns conntrack code), so prohibit
> hashsize modification if there is more than one netns exists.
> 
> To change hashtable sizes, you need to reload module.
> 
> Expectation hashtable size was simply glued to a variable with no code
> to rehash expectations, so it was a bug to allow writing to it.
> Make "expect_hashsize" readonly.
> 
> This is temporarily until we figure out what to do.

How about alternatively moving nf_conntrack_hsize into the
per-namespace struct? It doesn't look more complicated or
intrusive and would allow to still change the init_net
hashsize. Also seems less hackish :)
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