netdev - Re: [PATCH 6/7] mlx4_en: Adding rxhash support

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Message-ID: <1318964753.2407.7.camel@edumazet-laptop>
Date:	Tue, 18 Oct 2011 21:05:53 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jesse Brandeburg <jesse.brandeburg@...il.com>
Cc:	Stephen Hemminger <shemminger@...tta.com>,
	Yevgeny Petrilin <yevgenyp@...lanox.co.il>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH 6/7] mlx4_en: Adding rxhash support

Le mardi 18 octobre 2011 à 11:49 -0700, Jesse Brandeburg a écrit :
> On Tue, Oct 18, 2011 at 8:36 AM, Stephen Hemminger
> <shemminger@...tta.com> wrote:
> > On Tue, 18 Oct 2011 08:59:44 +0000
> > Yevgeny Petrilin <yevgenyp@...lanox.co.il> wrote:
> >> There is no gain in random values,
> >> I'll make the change to have static value for RSS function.
> >>
> >> We might consider how to ensure consistency across the different drivers in this aspect.
> >
> > The key should be part of the network device core. Almost all hardware just
> > implements the Microsoft standard, and if all drivers used same key they should
> > come up with the same hash.
> >
> > Although using the same key all the time makes testing easier.
> > The risk of using the same key is that it makes it easier for an attacker to
> > create a set of addresses that all map to the same CPU which would make a DoS
> > attack work better.  Therefore the key should be randomly generated at boot time.
> 
> Stephen, I respectfully disagree with your position here.  The risk of
> using the same key is that a malicious user could target a particular
> queue with a DoS attack, but how is that different than any single
> queue device?  NAPI protects a single queue against (a network
> interrupt based) DoS.  I do not think we should be generating a random
> key at boot time, and because of the way NAPI mitigates load, we are
> okay.  The gain from from the far simpler setup (and reproducability)
> outweighs the risk until someone can show damage due to this
> theoretical DoS attack.

Note : This policy could be up to the admin :

1) We could let admin chose a known hash for reproducability

   ethtool .... rss_hash xxxxxxxx:yyyyyyyy:zzzzzzzz:....

2) We could have a 'rss_perturb N ' ethtool option, to randomly reshufle
things every N seconds, for people really afraid ;)



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