linux-kernel - Re: [PATCH v4 17/17] mm/sl[au]b: check if large object is valid in _

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Date:   Tue, 23 Aug 2022 17:12:01 +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>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Marco Elver <elver@...gle.com>
Subject: Re: [PATCH v4 17/17] mm/sl[au]b: check if large object is valid in
 __ksize()

On 8/17/22 12:18, Hyeonggon Yoo wrote:
> If address of large object is not beginning of folio or size of
> the folio is too small, it must be invalid. BUG() in such cases.
> 
> Cc: Marco Elver <elver@...gle.com>
> Suggested-by: Vlastimil Babka <vbabka@...e.cz>
> Signed-off-by: Hyeonggon Yoo <42.hyeyoo@...il.com>
> Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
> ---
>  mm/slab_common.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 9c273a5fb0d7..98d029212682 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -984,8 +984,11 @@ size_t __ksize(const void *object)
>  
>  	folio = virt_to_folio(object);
>  
> -	if (unlikely(!folio_test_slab(folio)))
> +	if (unlikely(!folio_test_slab(folio))) {
> +		BUG_ON(folio_size(folio) <= KMALLOC_MAX_CACHE_SIZE);
> +		BUG_ON(object != folio_address(folio));
>  		return folio_size(folio);
> +	}
>  
>  	return slab_ksize(folio_slab(folio)->slab_cache);
>  }

In light of latest Linus' rant on BUG_ON() [1] I'm changing it to WARN_ON
and return 0, as it was in v3.

[1] https://lore.kernel.org/all/CAHk-=wiEAH+ojSpAgx_Ep=NKPWHU8AdO3V56BXcCsU97oYJ1EA@mail.gmail.com/


diff --git a/mm/slab_common.c b/mm/slab_common.c
index 98d029212682..a80c3a5e194d 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -985,8 +985,10 @@ size_t __ksize(const void *object)
 	folio = virt_to_folio(object);
 
 	if (unlikely(!folio_test_slab(folio))) {
-		BUG_ON(folio_size(folio) <= KMALLOC_MAX_CACHE_SIZE);
-		BUG_ON(object != folio_address(folio));
+		if (WARN_ON(folio_size(folio) <= KMALLOC_MAX_CACHE_SIZE))
+			return 0;
+		if (WARN_ON(object != folio_address(folio)))
+			return 0;
 		return folio_size(folio);
 	}