[PATCH][V2] backlight: sky81452: insure while loop does not allow negative array indexing

[Daniel Thompson]

On Thu, Feb 27, 2020 at 11:46:23AM +0000, Daniel Thompson wrote:
> On Wed, Feb 26, 2020 at 07:58:26PM +0000, Colin King wrote:
> > From: Colin Ian King <colin.king at canonical.com>
> > 
> > In the unlikely event that num_entry is zero, the while loop
> > pre-decrements num_entry to cause negative array indexing into the
> > array sources. Fix this by iterating only if num_entry >= 0.
> > 
> > Addresses-Coverity: ("Out-of-bounds read")
> > Fixes: f705806c9f35 ("backlight: Add support Skyworks SKY81452 backlight driver")
> > Signed-off-by: Colin Ian King <colin.king at canonical.com>
> > ---
> > 
> > V2: fix typo in commit subject line
> 
> Isn't the correct spelling "ensure"?
> 
> 
> > ---
> >  drivers/video/backlight/sky81452-backlight.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/video/backlight/sky81452-backlight.c b/drivers/video/backlight/sky81452-backlight.c
> > index 2355f00f5773..f456930ce78e 100644
> > --- a/drivers/video/backlight/sky81452-backlight.c
> > +++ b/drivers/video/backlight/sky81452-backlight.c
> > @@ -200,7 +200,7 @@ static struct sky81452_bl_platform_data *sky81452_bl_parse_dt(
> >  		}
> >  
> >  		pdata->enable = 0;
> > -		while (--num_entry)
> > +		while (--num_entry >= 0)
> >  			pdata->enable |= (1 << sources[num_entry]);
> 
> This look still looks buggy to me (so I'd second Walter's request to
> change it to a for loop). If the code genuinely does not contain a
> bug then it probably needs a prominent comment explaining why it is
> correct not to honour sources[0]!

Ignore the "still looks buggy". A mental mis-step when switching
contexts...

I think my English is still correct though ;-)


Daniel.