linux-kernel - Re: [PATCH 6/6] slab: don't validate slab pointer in free_debug

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Message-ID: <aMP7iOwAm-nC4ZYH@hyeyoo>
Date: Fri, 12 Sep 2025 19:52:56 +0900
From: Harry Yoo <harry.yoo@...cle.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Christoph Lameter <cl@...two.org>,
        David Rientjes <rientjes@...gle.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/6] slab: don't validate slab pointer in
 free_debug_processing()

On Thu, Sep 11, 2025 at 07:02:39PM +0200, Vlastimil Babka wrote:
> The struct slab pointer has been obtained one from the object being
> freed on all the paths that lead to this function. In all cases this
> already includes the test for slab type of the struct page which struct
> slab is overlaying. Thus we would not reach this function if it was
> not a valid slab pointer in the first place.
> 
> One less obvious case is that kmem_cache_free() trusts virt_to_slab()
> blindly so it may be NULL if the slab type check is false. But with
> SLAB_CONSISTENCY_CHECKS, cache_from_obj() called also from
> kmem_cache_free() catches this and returns NULL, which terminates
> freeing immediately.

Oh, I thought it'll crash even with debug caches
but it won't and I misread the code.

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

Looks good to me,
Reviewed-by: Harry Yoo <harry.yoo@...cle.com>

-- 
Cheers,
Harry / Hyeonggon