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

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Date:	Thu, 2 Dec 2010 13:55:34 -0500
From:	Jarod Wilson <jarod@...sonet.com>
To:	Dan Carpenter <error27@...il.com>
Cc:	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 Dec 2, 2010, at 10:00 AM, Jarod Wilson wrote:

> 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?

Never mind, I shouldn't be allowed near computers on too little sleep.
Its been pointed out to me how incredibly incorrect and stupid what I
said above is. :)

(i.e., we're not dividing the bits by 4, we're dividing a 64-bit value
by 4, so you're still in 62-bit territory.)

/me sticks head back in sand

-- 
Jarod Wilson
jarod@...sonet.com



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