linux-kernel - Re: [PATCH 8/8] platform: vivid-cec: fix potential integer overflow in vivid_cec_pin_adap

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Date:   Tue, 30 Jan 2018 02:51:41 -0600
From:   "Gustavo A. R. Silva" <garsilva@...eddedor.com>
To:     Hans Verkuil <hverkuil@...all.nl>
Cc:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 8/8] platform: vivid-cec: fix potential integer overflow
 in vivid_cec_pin_adap_events

Hi Hans,

Quoting Hans Verkuil <hverkuil@...all.nl>:

> Hi Gustavo,
>
> On 01/30/2018 01:33 AM, Gustavo A. R. Silva wrote:
>> Cast len to const u64 in order to avoid a potential integer
>> overflow. This variable is being used in a context that expects
>> an expression of type const u64.
>>
>> Addresses-Coverity-ID: 1454996 ("Unintentional integer overflow")
>> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
>> ---
>>  drivers/media/platform/vivid/vivid-cec.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/media/platform/vivid/vivid-cec.c  
>> b/drivers/media/platform/vivid/vivid-cec.c
>> index b55d278..30240ab 100644
>> --- a/drivers/media/platform/vivid/vivid-cec.c
>> +++ b/drivers/media/platform/vivid/vivid-cec.c
>> @@ -83,7 +83,7 @@ static void vivid_cec_pin_adap_events(struct  
>> cec_adapter *adap, ktime_t ts,
>>  	if (adap == NULL)
>>  		return;
>>  	ts = ktime_sub_us(ts, (CEC_TIM_START_BIT_TOTAL +
>> -			       len * 10 * CEC_TIM_DATA_BIT_TOTAL));
>> +			       (const u64)len * 10 * CEC_TIM_DATA_BIT_TOTAL));
>
> This makes no sense. Certainly the const part is pointless. And given that
> len is always <= 16 there definitely is no overflow.
>

Yeah, I understand your point and I know there is no chance of an  
overflow in this particular case.

> I don't really want this cast in the code.
>
> Sorry,
>

I'm working through all the Linux kernel Coverity reports, and I  
thought of sending a patch for this because IMHO it doesn't hurt to  
give the compiler complete information about the arithmetic in which  
an expression is intended to be evaluated.

I agree that the _const_ part is a bit odd. What do you think about  
the cast to u64 alone?

I appreciate your feedback.

Thanks
--
Gustavo