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

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Message-ID: <20150321052535.GB24466@acer.localdomain>
Date:	Sat, 21 Mar 2015 05:25:36 +0000
From:	Patrick McHardy <kaber@...sh.net>
To:	Thomas Graf <tgraf@...g.ch>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	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 20.03, Thomas Graf wrote:
> On 03/21/15 at 09:25am, Herbert Xu wrote:
> > On Fri, Mar 20, 2015 at 10:23:11PM +0000, Thomas Graf wrote:
> > > 
> > > He might as well just run for (;;) to burn cycles in his namespace.
> > > If you give away virtualized local privileges you better be ready
> > > to restrict the resources consumed. 
> > 
> > Please reread the first email that you replied to, let me quote:
> > 
> > 	A CPU intensive workload that can be rescheduled is
> > 	completely different from one that is running under spin
> > 	lock with BH disabled.
> 
> We have countless ways to create linear list of things like classifiers,
> qdiscs, multicast memberships, net_devices, fib_rules, etc. All taking
> spin locks or write locks. Most of them with BH disabled. Some at
> least use hashtables with most of them fixed size.

That's my point. Its impossible to fix this by restricting data
structures, this just removes a valid use case.

> I don't want to downplay this but do you *really* want to run
> untrusted workloads with CAP_NET_ADMIN privileges?
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