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

[Daniel Thompson]

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]!


Daniel.