linux-kernel - Re: [PATCH] mm: fix potential NULL pointer dereference in pagetable_alloc

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Message-ID: <53518ee0-d5fc-472e-bd67-0be5208b5b77@bytedance.com>
Date: Thu, 22 May 2025 14:58:57 +0800
From: Qi Zheng <zhengqi.arch@...edance.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Ye Chey <yechey@...sast.com>
Cc: akpm@...ux-foundation.org, david@...hat.com, Liam.Howlett@...cle.com,
 vbabka@...e.cz, rppt@...nel.org, surenb@...gle.com, mhocko@...e.com,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: fix potential NULL pointer dereference in
 pagetable_alloc_noprof



On 5/21/25 8:48 PM, Lorenzo Stoakes wrote:
> +cc mailing lists
> 
> Please ensure you always cc these when submitting patches by the way :)
> 
> On Wed, May 21, 2025 at 01:46:48PM +0100, Lorenzo Stoakes wrote:
>> On Wed, May 21, 2025 at 08:40:08PM +0800, Ye Chey wrote:
>>> The pagetable_alloc_noprof function does not check the return value of
>>> alloc_pages_noprof, which could lead to a NULL pointer dereference when
>>> memory allocation fails. Add a NULL check to prevent this issue.
>>>
>>> Signed-off-by: Ye Chey <yechey@...sast.com>
>>> ---
>>>   include/linux/mm.h | 3 ++-
>>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>>> index bf5520693..9052bb531 100644
>>> --- a/include/linux/mm.h
>>> +++ b/include/linux/mm.h
>>> @@ -3000,7 +3000,8 @@ static inline bool pagetable_is_reserved(struct ptdesc *pt)
>>>   static inline struct ptdesc *pagetable_alloc_noprof(gfp_t gfp, unsigned int order)
>>>   {
>>>   	struct page *page = alloc_pages_noprof(gfp | __GFP_COMP, order);
>>> -
>>> +	if (!page)
>>> +		return NULL;
>>>   	return page_ptdesc(page);
>>
>> Doesn't page_ptdesc() just cast the page to the appropriate type? And thus can
>> handle it being NULL?

Right, no NULL check is needed here.

>>
>>>   }
>>>   #define pagetable_alloc(...)	alloc_hooks(pagetable_alloc_noprof(__VA_ARGS__))
>>> --
>>> 2.44.0
>>>