Re: [PATCH v5] mm/slub: avoid accessing metadata when pointer is invalid in object_err()

[liqiong <liqiong@nfschina.com>]

在 2025/8/4 10:35, Harry Yoo 写道:
> 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@vger.kernel.org>
>>> Signed-off-by: Li Qiong <liqiong@nfschina.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@oracle.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())?

You're right, i ignored this situation.


>
>>> +		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