linux-kernel - Re: [PATCH] random32: avoid attempt to late reseed if in the middle of seeding

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Date:	Wed, 26 Mar 2014 19:35:01 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Daniel Borkmann <dborkman@...hat.com>
CC:	davem@...emloft.net, hannes@...essinduktion.org, tytso@....edu,
	linux-kernel@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH] random32: avoid attempt to late reseed if in the middle
 of seeding

On 03/26/2014 07:18 PM, Daniel Borkmann wrote:
> On 03/26/2014 06:12 PM, Sasha Levin wrote:
>> Commit 4af712e8df ("random32: add prandom_reseed_late() and call when
>> nonblocking pool becomes initialized") has added a late reseed stage
>> that happens as soon as the nonblocking pool is marked as initialized.
>>
>> This fails in the case that the nonblocking pool gets initialized
>> during __prandom_reseed()'s call to get_random_bytes(). In that case
>> we'd double back into __prandom_reseed() in an attempt to do a late
>> reseed - deadlocking on 'lock' early on in the boot process.
>>
>> Instead, just avoid even waiting to do a reseed if a reseed is already
>> occuring.
>>
>> Signed-off-by: Sasha Levin <sasha.levin@...cle.com>
>
> Thanks for catching! (If you want Dave to pick it up, please also
> Cc netdev.)
>
> Why not via spin_trylock_irqsave() ? Thus, if we already hold the
> lock, we do not bother any longer with doing the same work twice
> and just return.

Your code looks much better, I'll should really stop sending patches
too early in the morning...

It's also worth adding lib/random32.c to the MAINTAINERS file, as my
list of recipients is solely based on what get_maintainer.pl tells
me to do (and I'm assuming that I'm not the last person who will be
sending patches for this).


Thanks,
Sasha
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