Re: [PATCH] mm: fix potential NULL pointer dereference in pagetable_alloc_noprof

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

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