linux-kernel - Re: [PATCH v6] mm/slub: avoid accessing metadata when pointer is invalid in object

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Message-ID: <aJH7VQzyPwbKayQ4@hyeyoo>
Date: Tue, 5 Aug 2025 21:38:45 +0900
From: Harry Yoo <harry.yoo@...cle.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Li Qiong <liqiong@...china.com>, Christoph Lameter <cl@...two.org>,
        David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v6] mm/slub: avoid accessing metadata when pointer is
 invalid in object_err()

On Mon, Aug 04, 2025 at 05:19:59PM +0200, Vlastimil Babka wrote:
> On 8/4/25 04:57, 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 the pointer is NULL or check_valid_pointer() returns false for
> > the pointer, only print the pointer value and skip accessing metadata.
> 
> We should explain that this is not theoretical so justify the stable cc, so
> I would add:
> 
> One known path to the crash is when alloc_consistency_checks() determines
> the pointer to the allocated object is invalid beause of a freelist

nit: beause -> because

> corruption, and calls object_err() to report it. The debug code should
> report and handle the corruption gracefully and not crash in the process.
>
> If you agree, I can do this when picking up the patch after merge window, no
> need to resend.
>
> > Fixes: 81819f0fc828 ("SLUB core")
> > Cc: <stable@...r.kernel.org>
> > Signed-off-by: Li Qiong <liqiong@...china.com>
> > ---

Reviewed-by: Harry Yoo <harry.yoo@...cle.com>

-- 
Cheers,
Harry / Hyeonggon