linux-kernel - Re: [PATCH v2] mm: slub: avoid deref of free pointer in sanity checks if object is invalid

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Message-ID: <e6f14d8a-5d32-473e-ba2d-1064ab8ef8fe@nfschina.com>
Date: Mon, 28 Jul 2025 10:06:42 +0800
From: liqiong <liqiong@...china.com>
To: Harry Yoo <harry.yoo@...cle.com>, Matthew Wilcox <willy@...radead.org>
Cc: Vlastimil Babka <vbabka@...e.cz>, 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
Subject: Re: [PATCH v2] mm: slub: avoid deref of free pointer in sanity checks
 if object is invalid



在 2025/7/26 07:00, Harry Yoo 写道:
> On Sat, Jul 26, 2025 at 04:55:06AM +0900, Harry Yoo wrote:
>> On Fri, Jul 25, 2025 at 06:10:51PM +0100, Matthew Wilcox wrote:
>>> On Fri, Jul 25, 2025 at 06:47:01PM +0200, Vlastimil Babka wrote:
>>>> On 7/25/25 08:49, Li Qiong wrote:
>>>>> For debugging, object_err() prints free pointer of the object.
>>>>> However, if check_valid_pointer() returns false for a object,
>>>>> dereferncing `object + s->offset` can lead to a crash. Therefore,
>>>>> print the object's address in such cases.
>>>>>  	if (!check_valid_pointer(s, slab, object)) {
>>>>> -		object_err(s, slab, object, "Freelist Pointer check fails");
>>>>> +		slab_err(s, slab, "Invalid object pointer 0x%p", object);
>>>>>  		return 0;
>>> No, the error message is now wrong.  It's not an object, it's the
>>> freelist pointer.
>> Because it's the object is about to be allocated, it will look like
>> this:
>>
>>   object pointer -> obj: [ garbage ][   freelist pointer   ][ garbage ]
>>
>> SLUB uses check_valid_pointer() to check either 1) freelist pointer of
>> an object is valid (e.g. in check_object()), or 2) an object pointer
>> points to a valid address (e.g. in free_debug_processing()).
>>
>> In this case it's an object pointer, not a freelist pointer.
>> Or am I misunderstanding something?
> Actually, in alloc_debug_processing() the pointer came from slab->freelist,
> so I think saying either "invalid freelist pointer" or
> "invalid object pointer" make sense...

free_consistency_checks()  has 
 'slab_err(s, slab, "Invalid object pointer 0x%p", object);'
Maybe  it is better, alloc_consisency_checks() has the same  message.





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