Re: [PATCH 2/3] slab: don't put freepointer outside of object if only orig_size

[Vlastimil Babka]

On 5/28/24 9:16 AM, Chengming Zhou wrote:
> The commit 946fa0dbf2d8 ("mm/slub: extend redzone check to extra
> allocated kmalloc space than requested") will extend right redzone
> when allocating for orig_size < object_size. So we can't overlay the
> freepointer in the object space in this case.
> 
> But the code looks like it forgot to check SLAB_RED_ZONE, since there
> won't be extended right redzone if only orig_size enabled.
> 
> Signed-off-by: Chengming Zhou <chengming.zhou@xxxxxxxxx>

Seems OK.

> ---
>  mm/slub.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index de57512734ac..b92d9a557852 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -5150,7 +5150,7 @@ static int calculate_sizes(struct kmem_cache *s)
>  	 */
>  	s->inuse = size;
>  
> -	if (slub_debug_orig_size(s) ||
> +	if (((flags & SLAB_RED_ZONE) && slub_debug_orig_size(s)) ||
>  	    (flags & (SLAB_TYPESAFE_BY_RCU | SLAB_POISON)) ||
>  	    ((flags & SLAB_RED_ZONE) && s->object_size < sizeof(void *)) ||

Should we consolidate the two cases with flags & SLAB_RED_ZONE?

Also below this is a comment that could also mention the slub_debug_orig_size().

>  	    s->ctor) {
>