netdev - Re: [v1 PATCH 7/14] netfilter: Use rhashtable_lookup instead of lookup

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Message-ID: <20150320215756.GA24045@gondor.apana.org.au>
Date:	Sat, 21 Mar 2015 08:57:56 +1100
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Thomas Graf <tgraf@...g.ch>
Cc:	Patrick McHardy <kaber@...sh.net>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [v1 PATCH 7/14] netfilter: Use rhashtable_lookup instead of
 lookup_compare

On Fri, Mar 20, 2015 at 09:56:12PM +0000, Thomas Graf wrote:
> On 03/21/15 at 08:47am, Herbert Xu wrote:
> > On Fri, Mar 20, 2015 at 10:27:01AM +0000, Patrick McHardy wrote:
> > > On 20.03, Herbert Xu wrote:
> > >
> > > > Any hash function can be attacked.  That's why we need to be able
> > > > to rehash it.  And the best way to decide when to rehash is based
> > > > on chain length (otherwise you'd waste time rehashing periodically
> > > > like we used to do).  With name spaces these days anyone could be
> > > > an adversary.
> > > 
> > > We already had this discussion. I strongly do not believe this is
> > > the right way to fix namespace problems. There are millions of ways
> > > of creating CPU intensive workloads. You need to be able to put
> > > bounds on the entire namespace. Fixing individual spots will not
> > > solve that problem.
> > 
> > A CPU intensive workload that can be rescheduled is completely
> > different from one that is running under spin lock with BH disabled.
> 
> Just make the chain length based growth function configurable
> and nft_hash can disable it. nft_hash entries are not created by
> unprivileged users so attacking the table is out of the question.

Please read the quoted text, we're talking about potential attacks
on nft_hash.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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