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

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Date:	Fri, 05 Feb 2010 05:14:10 -0500
From:	Jon Masters <jonathan@...masters.org>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	Alexey Dobriyan <adobriyan@...il.com>, davem@...emloft.net,
	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

On Fri, 2010-02-05 at 11:00 +0100, Patrick McHardy wrote:
> Jon Masters wrote:
> > On Thu, 2010-02-04 at 17:27 +0100, Patrick McHardy wrote:
> >> Patrick McHardy wrote:
> >>> 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 :)
> >> Just to avoid duplicate work, I'm currently trying that.
> > 
> > Bah. I already worked a set of patches to do that as I mentioned, but
> > you've probably done it by now - can clean up and post if not :)
> 
> Sorry, I missed that in your mail. I'm pretty much done, will finish
> testing shortly.

Oh, it's cool. I hacked it together on my test box but I'm happy to go
with whatever you post later, I will just try to be forthcoming next
time with my bits first to save you hassle. Please do keep CCing me on
these things and I'll try to test over the weekend as time permits.

Jon.


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