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

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Date:	Thu, 7 May 2009 20:21:04 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Matt Mackall <mpm@...enic.com>
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

* Matt Mackall <mpm@...enic.com> wrote:

> >  aldebaran:~/l> ./lat_proc fork
> >  Process fork+exit: 61.7865 microseconds
> 
> Uh, what? There's no exec() involved in fork+exit, so hopefully 
> ASLR doesn't decide to make an appearance.

We use it to seed the per task stackprotector secret. Look for 
get_random_int() in kernel/fork.c.

(
  Now, if get_random_int() slows down we could certainly water that 
  down and have a system-wide secret and some easy and fast 
  long-cycle permutation code to make it not so easy to figure out 
  the core secret from a kernel crash signature.

  [ Alas, that might be worth doing in any case - to not have 
    get_random_int() in the clone() / pthread_create() fastpath. ]

  We really need a design decision there - if get_random_int() is 
  supposed to be a mathematically safe hash, ignoring the physics of 
  the world, then we need a separate get_random_int_fast() API or 
  so. All current users of get_random_int() will evaporate as well. 
)

	Ingo
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