linux-kernel - Re: [PATCH] media: rc: ir-lirc-codec: fix potential integer overflow

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Date:	Thu, 2 Dec 2010 10:00:45 -0500
From:	Jarod Wilson <jarod@...hat.com>
To:	Dan Carpenter <error27@...il.com>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	kernel-janitors@...r.kernel.org,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	David Härdeman <david@...deman.nu>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: rc: ir-lirc-codec: fix potential integer overflow

On Thu, Dec 02, 2010 at 07:51:26AM +0300, Dan Carpenter wrote:
> On Fri, Nov 26, 2010 at 08:06:35PM +0300, Vasiliy Kulikov wrote:
> >  	count = n / sizeof(int);
> > -	if (count > LIRCBUF_SIZE || count % 2 == 0)
> > +	if (count > LIRCBUF_SIZE || count % 2 == 0 || n % sizeof(int) != 0)
>                                                       ^^^^^^^^^^^^^^^^^^^^
> 
> Wait, what?  We just checked this a couple lines before.

Bah. I'd only looked at the diff, which didn't have enough context. I
thought that looked familiar. Indeed, this part seems to be unnecessary.

> The rest of the patch is right and a clever catch.  It would affect 
> x86_64 systems and not i386.  This doesn't have security implications
> does it?  You'd just catch the kmalloc() stack trace for insanely large
> allocations.

Even on x86_64, it looks to my (relatively untrained) eye like you'd
actually be fine. n is a size_t (so, 64-bit on x86_64). count is an int
(so 32-bit on x86_64). We initialize count to some 64-bit value / 4, so
at most, 16 bits, which always fits just fine in the 32-bit int, no?

-- 
Jarod Wilson
jarod@...hat.com

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