linux-kernel - Re: [linux-next-20130422] Bug in SLAB?

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Message-Id: <201305071938.DAC81273.HOSJOFFOQLtMFV@I-love.SAKURA.ne.jp>
Date:	Tue, 7 May 2013 19:38:12 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	cl@...ux.com
Cc:	glommer@...allels.com, penberg@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [linux-next-20130422] Bug in SLAB?

Christoph Lameter wrote:
> On Sat, 4 May 2013, Tetsuo Handa wrote:
> 
> > Christoph Lameter wrote:
> > > Ok could I see the kernel logs with the warnings?
> > Sure.
> 
> These are exclusively from the module load. So the kernel seems to be
> clean of large kmalloc's ?
> 
There are modules (e.g. TOMOYO) which do not check for KMALLOC_MAX_SIZE limit
and expect kmalloc() larger than KMALLOC_MAX_SIZE bytes to return NULL.

As far as I know, such modules sequentially double the buffer size. Therefore,
as long as request for KMALLOC_MAX_SIZE * 2 bytes returns NULL, they won't
trigger oops by requesting for KMALLOC_MAX_SIZE * 8 bytes.

The testcase I wrote is for module (I don't know if there is one) which
requests for KMALLOC_MAX_SIZE * 8 bytes without requesting for
KMALLOC_MAX_SIZE * 2 bytes and/or KMALLOC_MAX_SIZE * 4 bytes.
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