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

[Gustavo A. R. Silva]

Hi Hans,

Quoting Hans Verkuil <hverkuil@xxxxxxxxx>:

> 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@xxxxxxxxxxxxxx>
> > ---
> >  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