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

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Message-ID: <4c8406b7-f5eb-4907-8ee1-f997bdeb157c@linux.dev>
Date: Mon, 3 Jun 2024 17:40:24 +0800
From: Chengming Zhou <chengming.zhou@...ux.dev>
To: Vlastimil Babka <vbabka@...e.cz>, 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>,
 Roman Gushchin <roman.gushchin@...ux.dev>,
 Hyeonggon Yoo <42.hyeyoo@...il.com>, Feng Tang <feng.tang@...el.com>
Cc: 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 2024/6/3 17:25, Vlastimil Babka wrote:
> 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@...ux.dev>
> 
> 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?

Yes, we can.

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

Ok, will add.

Thanks.

> 
>>  	    s->ctor) {
>>
>