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From: daw@cs.berkeley.edu (David Wagner)
To: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] ELF: implement AT_RANDOM for future glibc use
Date: Mon, 6 Oct 2008 18:25:46 +0000 (UTC)	[thread overview]
Message-ID: <gcdl7a$en4$1@taverner.cs.berkeley.edu> (raw)
In-Reply-To: <20081006175038.GF10357@outflux.net>

Kees Cook  wrote:
>On Mon, Oct 06, 2008 at 08:00:21AM +0200, Andi Kleen wrote:
>> While the basic idea is good using get_random_bytes() is not.
>> 
>> That eats precious cryptography strength entropy from the entropy
>> pool, which on many systems is not adequately fed. In those cases you
>> really only want to use it for real keys, not for lower grade
>> applications. The applications glibc wants to use this for do not
>> really require crypto strength entropy, just relatively unpredictable
>> randomness.
>
>We're already using get_random* for stack, heap, and brk.  Also,
>get_random* uses the nonblocking pool, so this is the same as if userspace
>had tried to pull bytes out of /dev/urandom, which (as I understand it)
>is the very thing we're trying to duplicate without the VFS overhead.

Using /dev/urandom does seem like exactly the right thing to do.
(Andi Kleen's criticisms would be relevant if get_random_bytes() acted
like reading from /dev/random.)

I don't think it would be wise to use less than crypto strength
pseudorandom numbers for glibc -- at least, not without very thorough
analysis.  glibc is using this for security, so it has to be right.
When people say "oh, we don't need crypto-strength randomness", in
my experience it's too common to end up with something insecure.

  reply	other threads:[~2008-10-06 18:25 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20081001201116.GD12527@outflux.net>
     [not found] ` <48E3EFD6.2010704@redhat.com>
     [not found]   ` <20081001215657.GH12527@outflux.net>
     [not found]     ` <20081001220948.GC32107@sunsite.ms.mff.cuni.cz>
     [not found]       ` <20081001222706.68E7E1544B4@magilla.localdomain>
2008-10-03  0:16         ` Kees Cook
2008-10-03  0:43           ` Jakub Jelinek
2008-10-03  5:25             ` Kees Cook
2008-10-03  5:29             ` Kees Cook
2008-10-03  5:57               ` Arjan van de Ven
2008-10-03  6:25                 ` Ulrich Drepper
2008-10-03 14:50                   ` [PATCH] ELF: implement AT_RANDOM for glibc PRNG seeding Kees Cook
2008-10-03 14:56                     ` Ulrich Drepper
2008-10-03 14:57                     ` Jakub Jelinek
2008-10-03 17:33                       ` Kees Cook
2008-10-03 17:41                         ` Ulrich Drepper
2008-10-03 17:59                           ` [PATCH v5] " Kees Cook
2008-10-18  5:42                             ` Ulrich Drepper
2008-10-21 20:01                             ` Andrew Morton
2008-10-21 20:22                               ` Ulrich Drepper
2008-10-27  5:46                                 ` Andrew Morton
2008-10-03  0:52           ` [PATCH] ELF: implement AT_RANDOM for future glibc use Roland McGrath
2008-10-03  5:15             ` Kees Cook
2008-10-03 20:22               ` Roland McGrath
2008-10-06  6:00           ` Andi Kleen
2008-10-06 17:50             ` Kees Cook
2008-10-06 18:25               ` David Wagner [this message]
2008-10-06 20:23                 ` Andi Kleen
2008-10-06 22:16                   ` David Wagner
2008-10-06 19:26               ` Andi Kleen
2008-10-06 22:01                 ` Kees Cook
2008-10-06 23:19                   ` Andi Kleen
2008-10-06 23:29                     ` Kees Cook
2008-10-06 23:44                       ` Andi Kleen
2008-10-06 22:07                 ` Kees Cook
2008-10-06 23:28                   ` Andi Kleen
2008-10-06 23:58                   ` Roland McGrath
2008-10-07  0:08                     ` Ulrich Drepper
2008-10-07  0:31                     ` Kees Cook
2008-10-07  0:57                       ` Ulrich Drepper
2008-10-07  1:44                         ` Kees Cook
2008-10-07  1:51                           ` Ulrich Drepper

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