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

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Date:	Tue, 5 May 2009 08:35:35 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
cc:	security@...nel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Eric Paris <eparis@...hat.com>, Jake Edge <jake@....net>,
	linux-security-module@...r.kernel.org, mingo@...hat.com,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Matt Mackall <mpm@...enic.com>,
	James Morris <jmorris@...ei.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Roland McGrath <roland@...hat.com>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [Security] [PATCH] proc: avoid information leaks to non-privileged
 processes



On Tue, 5 May 2009, Linus Torvalds wrote:
> 
> Note: the "pid + jiffies" is just meant to be a tiny tiny bit of noise. It 
> has no real meaning. It could be anything. I just picked the previous 
> seed, it's just that now we keep the state in between calls and that will 
> feed into the next result, and that should make all the difference.

Actually, thinking about it, we could/should probably just remove that 
tiny bit of noise.

After all, we get _real_ noise from the "keyptr->secret" thing. It's not 
updated all the time, but it's certainly updated often enough that nobody 
will ever see anything remotely guessable, I suspect.

Not that the "pid+jiffies" should hurt either, of course. It just doesn't 
really look meaningful, and only exists as a historical oddity that 
relates to the previous implementation of get_random_int().

			Linus
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