Re: [PATCH 4/4] lib/vsprintf: add missing (u8) cast in format_decode() lookup

[Petr Mladek]

On Tue 2026-03-24 22:49:40, Josh Law wrote:
> The first lookup into the format_state table correctly casts to (u8)
> at line 2778, but the second lookup after consuming a length qualifier
> does not. On signed-char platforms, a byte >= 0x80 sign-extends to a
> negative index, reading before the array.
> 
> Add the same (u8) cast for consistency.
> 
> Signed-off-by: Josh Law <objecting@xxxxxxxxxxxxx>
> ---
>  lib/vsprintf.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 2758096b6f53..3108823e8c22 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -2783,7 +2783,7 @@ struct fmt format_decode(struct fmt fmt, struct printf_spec *spec)
>  			fmt.str++;
>  		}
>  		fmt.str++;
> -		p = lookup_state + *fmt.str;
> +		p = lookup_state + (u8)*fmt.str;
>  	}
>  	if (p->state) {
>  		if (p->base)

This makes sense. Even though the current code is safe as pointed
out by Andy.

Reviewed-by: Petr Mladek <pmladek@xxxxxxxx>

Best Regards,
Petr