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

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Message-ID: <20150320220751.GB566@casper.infradead.org>
Date:	Fri, 20 Mar 2015 22:07:51 +0000
From:	Thomas Graf <tgraf@...g.ch>
To:	Herbert Xu <herbert@...dor.apana.org.au>
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 03/21/15 at 08:57am, Herbert Xu wrote:
> 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:
> > > > 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.

Attack by whom? If I read the nft_set code correctly then the only
way to add to an nft_set is via nfnetlink which requires
CAP_NET_ADMIN. My understanding was that the chain length based
growth is to counter hash seed attacks.
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