linux-kernel - Re: [PATCH 16/16] mm/sl[au]b: check if large object is valid in _

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Date:   Fri, 29 Jul 2022 13:50:50 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Hyeonggon Yoo <42.hyeyoo@...il.com>,
        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>,
        Joe Perches <joe@...ches.com>,
        Vasily Averin <vasily.averin@...ux.dev>,
        Matthew WilCox <willy@...radead.org>,
        Marco Elver <elver@...gle.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 16/16] mm/sl[au]b: check if large object is valid in
 __ksize()

On 7/12/22 15:39, Hyeonggon Yoo wrote:
> __ksize() returns size of objects allocated from slab allocator.
> When invalid object is passed to __ksize(), returning zero
> prevents further memory corruption and makes caller be able to
> check if there is an error.
> 
> If address of large object is not beginning of folio or size of
> the folio is too small, it must be invalid. Return zero in such cases.
> 
> Suggested-by: Vlastimil Babka <vbabka@...e.cz>
> Signed-off-by: Hyeonggon Yoo <42.hyeyoo@...il.com>

Reviewed-by: Vlastimil Babka <vbabka@...e.cz>

If you want to change it to BUG() I won't object, no strong opinion.

> ---
>  mm/slab_common.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 1f8db7959366..0d6cbe9d7ad0 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -1013,8 +1013,12 @@ size_t __ksize(const void *object)
>  
>  	folio = virt_to_folio(object);
>  
> -	if (unlikely(!folio_test_slab(folio)))
> +	if (unlikely(!folio_test_slab(folio))) {
> +		if (WARN_ON(object != folio_address(folio) ||
> +				folio_size(folio) <= KMALLOC_MAX_CACHE_SIZE))
> +			return 0;
>  		return folio_size(folio);
> +	}
>  
>  	return slab_ksize(folio_slab(folio)->slab_cache);
>  }