linux-kernel - Re: [PATCH v3] mm: slub: avoid deref of free pointer in sanity checks if object is invalid

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Message-ID: <8e9fb1b0-8da9-48aa-ac2c-ac4634ba5f7b@nfschina.com>
Date: Wed, 30 Jul 2025 16:36:45 +0800
From: liqiong <liqiong@...china.com>
To: Harry Yoo <harry.yoo@...cle.com>
Cc: David Rientjes <rientjes@...gle.com>,
 Andrew Morton <akpm@...ux-foundation.org>, Vlastimil Babka <vbabka@...e.cz>,
 Roman Gushchin <roman.gushchin@...ux.dev>, linux-kernel@...r.kernel.org,
 stable@...r.kernel.org
Subject: Re: [PATCH v3] mm: slub: avoid deref of free pointer in sanity checks
 if object is invalid



在 2025/7/30 13:04, Harry Yoo 写道:
> On Wed, Jul 30, 2025 at 09:46:09AM +0800, liqiong wrote:
>> 在 2025/7/29 21:41, Harry Yoo 写道:
>>> On Tue, Jul 29, 2025 at 04:14:55PM +0800, Li Qiong wrote:
>>>> Fixes: bb192ed9aa71 ("mm/slub: Convert most struct page to struct slab by spatch")
>>> As Vlastimil mentioned in previous version, this is not the first commit
>>> that introduced this problem.
> Please don't forget to update Fixes: tag :)

It seems that it's the first commit:    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().
>>>> ---
>>>>  mm/slub.c | 8 ++++++--
>>>>  1 file changed, 6 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/mm/slub.c b/mm/slub.c
>>>> index 31e11ef256f9..d3abae5a2193 100644
>>>> --- a/mm/slub.c
>>>> +++ b/mm/slub.c
>>>> @@ -1104,7 +1104,11 @@ 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)) {
>>>> +		print_slab_info(slab);
>>>> +		pr_err("invalid object 0x%p\n", object);
>>> Can we just handle this inside print_trailer() because that's the function
>>> that prints the object's free pointer, metadata, etc.?
>> Maybe it's clearer ,  if  object pointer being invalid, don't enter print_trailer()，
>> print_trailer() prints  valid object.
> You're probably right. No strong opinion.
> object_err() is the only user anyway.
>
>>>> +	} else
>>>> +		print_trailer(s, slab, object);
>>>>  	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
>>>>  
>>>>  	WARN_ON(1);
>>>> @@ -1587,7 +1591,7 @@ static inline int alloc_consistency_checks(struct kmem_cache *s,
>>>>  		return 0;
>>>>  
>>>>  	if (!check_valid_pointer(s, slab, object)) {
>>>> -		object_err(s, slab, object, "Freelist Pointer check fails");
>>>> +		slab_err(s, slab, "Freelist Pointer(0x%p) check fails", object);
>>>>  		return 0;
>>> Do we really need this hunk after making object_err() resiliant
>>> against wild pointers?
>> That's the origin issue,   it may be  inappropriate to use object_err(), if check_valid_pointer being false.
> That was the original issue, but you're making it not crash even if
> with bad pointers are passed?

Make sense, fix in object_err(),  it wouldn't  crash and print the message.

>
>>>>  	}