* Re: [PATCH] mm: slub: fix dereference invalid pointer in alloc_consistency_checks
[not found] <20250725024854.1201926-1-liqiong@nfschina.com>
@ 2025-07-25 4:01 ` Harry Yoo
0 siblings, 0 replies; only message in thread
From: Harry Yoo @ 2025-07-25 4:01 UTC (permalink / raw)
To: Li Qiong
Cc: Christoph Lameter, David Rientjes, Andrew Morton, Vlastimil Babka,
Roman Gushchin, linux-mm, linux-kernel, stable
On Fri, Jul 25, 2025 at 10:48:54AM +0800, Li Qiong wrote:
> In object_err(), need dereference the 'object' pointer, it may cause
> a invalid pointer fault. Use slab_err() instead.
Hi Li Qiong, this patch makes sense to me.
But I'd suggest to rephrase it a little bit, like:
mm/slab: avoid deref of free pointer in sanity checks if object is invalid
For debugging purposes, object_err() prints free pointer of the object.
However, if check_valid_pointer() returns false for object,
`object + s->offset` is also invalid and dereferncing it can lead to a
crash. Therefore, avoid dereferencing it and only print the object's
address in such cases.
> Signed-off-by: Li Qiong <liqiong@nfschina.com>
Which commit introduced this problem?
A Fixes: tag is needed to determine which -stable versions it should be
backported to.
And to backport MM patches to -stable, you need to explicitly add
'Cc: stable@vger.kernel.org' to the patch.
> ---
> mm/slub.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 31e11ef256f9..3a2e57e2e2d7 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1587,7 +1587,7 @@ static inline int alloc_consistency_checks(struct kmem_cache *s,
> return 0;
>
> if (!check_valid_pointer(s, slab, object)) {
> - object_err(s, slab, object, "Freelist Pointer check fails");
> + slab_err(s, slab, "Freelist Pointer (0x%p) check fails", object);
Can this be
slab_err(s, slab, "Invalid object pointer 0x%p", object);
to align with free_consistency_checks()?
> return 0;
> }
>
It might be worth adding a comment in object_err() stating that it should
only be called when check_valid_pointer() returns true for object, and
a WARN_ON_ONCE(!check_valid_pointer(s, slab, object)) to catch incorrect
usages?
--
Cheers,
Harry / Hyeonggon
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