linux-kernel - Re: [PATCH 2/3] slab: don't put freepointer outside of object if only orig

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Date: Tue, 28 May 2024 21:05:26 +0800
From: Feng Tang <feng.tang@...el.com>
To: Chengming Zhou <chengming.zhou@...ux.dev>
CC: Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>, David
 Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>, Andrew
 Morton <akpm@...ux-foundation.org>, Vlastimil Babka <vbabka@...e.cz>, Roman
 Gushchin <roman.gushchin@...ux.dev>, Hyeonggon Yoo <42.hyeyoo@...il.com>,
	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
	<zhouchengming@...edance.com>
Subject: Re: [PATCH 2/3] slab: don't put freepointer outside of object if
 only orig_size

On Tue, May 28, 2024 at 03:16:47PM +0800, 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.

Look good to me. Thanks!

Reviewed-by: Feng Tang <feng.tang@...el.com>

> 
> Signed-off-by: Chengming Zhou <chengming.zhou@...ux.dev>
> ---
>  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 *)) ||
>  	    s->ctor) {
> 
> -- 
> 2.45.1
>