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

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Message-ID: <20150321052325.GA24466@acer.localdomain>
Date:	Sat, 21 Mar 2015 05:23:26 +0000
From:	Patrick McHardy <kaber@...sh.net>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Thomas Graf <tgraf@...g.ch>, 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 21.03, 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.

Sure, that's what I actually meant of course.
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