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

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Message-ID: <bc6f3549-2e92-4132-8e2d-bed027d156f9@nfschina.com>
Date: Tue, 5 Aug 2025 09:24:04 +0800
From: liqiong <liqiong@...china.com>
To: Vlastimil Babka <vbabka@...e.cz>, Christoph Lameter <cl@...two.org>,
 David Rientjes <rientjes@...gle.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: Harry Yoo <harry.yoo@...cle.com>, 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()



在 2025/8/4 23:19, Vlastimil Babka 写道:
> 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
> 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.

Agree, thanks.


>> 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.
>> v6:
>> - add checking 'object' if NULL.
>> ---
>>  mm/slub.c | 7 ++++++-
>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/slub.c b/mm/slub.c
>> index 31e11ef256f9..972cf2bb2ee6 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 (!object || !check_valid_pointer(s, slab, object)) {
>> +		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);