linux-kernel - Re: [Security] [PATCH] proc: avoid information leaks to non-privileged processes

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Message-ID: <20090507192432.GN31071@waste.org>
Date:	Thu, 7 May 2009 14:24:32 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Jake Edge <jake@....net>, security@...nel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	James Morris <jmorris@...ei.org>,
	linux-security-module@...r.kernel.org,
	Eric Paris <eparis@...hat.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Roland McGrath <roland@...hat.com>, mingo@...hat.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg KH <greg@...ah.com>, Dave Jones <davej@...hat.com>
Subject: Re: [Security] [PATCH] proc: avoid information leaks to non-privileged processes

On Thu, May 07, 2009 at 08:41:36PM +0200, Ingo Molnar wrote:
> 
> * Matt Mackall <mpm@...enic.com> wrote:
> 
> > > As i mentioned it in the previous mail, i'd _really_ like to 
> > > hear your thread model and attack vector description. Does this 
> > > overhead justify the threat? Your change will only result in 
> > > get_random_int() not being considered fast anymore.
> > 
> > My threat model is that someone more clever and with a lot more 
> > expertise attacking systems than either you or me will be able to 
> > leverage the extreme weakness of this hash (O(1) attacks against 
> > the *full* version!) into an attack that incrementally exposes the 
> > hidden RNG state. I've asked a couple such people whether they 
> > think that's likely, and they've said yes.
> 
> My question was whether the variant laced with the cycle counter 
> could be exposable.

In my world, some machines don't have TSCs, so I think this is the
wrong question to be asking.

-- 
Mathematics is the supreme nostalgia of our time.
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