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

From: Jarod Wilson
Date: Thu Dec 02 2010 - 13:55:42 EST


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@xxxxxxxxxxxx



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