linux-kernel - Re: [PATCH v5] mm/slub: avoid accessing metadata when pointer is invalid in object

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Message-ID: <aJAcjcBOcKCDPwjY@hyeyoo>
Date: Mon, 4 Aug 2025 11:35:57 +0900
From: Harry Yoo <harry.yoo@...cle.com>
To: Li Qiong <liqiong@...china.com>
Cc: Christoph Lameter <cl@...two.org>, David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Roman Gushchin <roman.gushchin@...ux.dev>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v5] mm/slub: avoid accessing metadata when pointer is
 invalid in object_err()

On Mon, Aug 04, 2025 at 11:25:23AM +0900, Harry Yoo wrote:
> On Mon, Aug 04, 2025 at 09:46:25AM +0800, Li Qiong wrote:
> > object_err() reports details of an object for further debugging, such as
> > the freelist pointer, redzone, etc. However, if the pointer is invalid,
> > attempting to access object metadata can lead to a crash since it does
> > not point to a valid object.
> > 
> > In case check_valid_pointer() returns false for the pointer, only print
> > the pointer value and skip accessing metadata.
> > 
> > Fixes: 81819f0fc828 ("SLUB core")
> > Cc: <stable@...r.kernel.org>
> > Signed-off-by: Li Qiong <liqiong@...china.com>
> > ---
> > v2:
> > - rephrase the commit message, add comment for object_err().
> > v3:
> > - check object pointer in object_err().
> > v4:
> > - restore changes in alloc_consistency_checks().
> > v5:
> > - rephrase message, fix code style.
> > ---
> 
> Looks good to me,
> Reviewed-by: Harry Yoo <harry.yoo@...cle.com>
> 
> -- 
> Cheers,
> Harry / Hyeonggon
> 
> >  mm/slub.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> > 
> > diff --git a/mm/slub.c b/mm/slub.c
> > index 31e11ef256f9..b3eff1476c85 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -1104,7 +1104,12 @@ static void object_err(struct kmem_cache *s, struct slab *slab,
> >  		return;
> >  
> >  	slab_bug(s, reason);
> > -	print_trailer(s, slab, object);
> > +	if (!check_valid_pointer(s, slab, object)) {

Wait, hold on. check_valid_pointer() returns true when object == NULL.
the condition should be (!object || !check_valid_pointer())?

> > +		print_slab_info(slab);
> > +		pr_err("Invalid pointer 0x%p\n", object);
> > +	} else {
> > +		print_trailer(s, slab, object);
> > +	}
> >  	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
> >  
> >  	WARN_ON(1);
> > -- 
> > 2.30.2

-- 
Cheers,
Harry / Hyeonggon