Re: [PATCH] mm: handle potential NULL return from anon_vma_name_reuse()

[Lorenzo Stoakes <ljs@kernel.org>]

On Tue, Apr 21, 2026 at 10:55:16AM +0200, David Hildenbrand (Arm) wrote:
> On 4/21/26 10:50, Ye Liu wrote:
> > From: Ye Liu <liuye@kylinos.cn>
> >
> > The anon_vma_name_reuse() function may return NULL if memory allocation
> > fails in anon_vma_name_alloc(). Currently, callers dup_anon_vma_name()
> > and replace_anon_vma_name() do not check the return value, which could
> > lead to NULL pointer dereferences.
>
> When, where?
>
> If we set vma->anon_name = NULL, it just looks like there is no anon
> VMA, or what am I missing?
>
> >
> > This patch adds proper error handling:
> > - In dup_anon_vma_name(), if anon_vma_name_reuse() returns NULL, emit a
> >   warning via WARN_ON_ONCE(1) since this is an unexpected condition.
> > - In replace_anon_vma_name(), return -ENOMEM to propagate the allocation
> >   failure to the caller.
> >
> > These changes improve robustness against memory allocation failures.
> >
> > Signed-off-by: Ye Liu <liuye@kylinos.cn>
> > ---
> >  include/linux/mm_inline.h | 12 +++++++++---
> >  mm/madvise.c              |  7 ++++++-
> >  2 files changed, 15 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
> > index a171070e15f0..9bbaf8287806 100644
> > --- a/include/linux/mm_inline.h
> > +++ b/include/linux/mm_inline.h
> > @@ -421,9 +421,15 @@ static inline void dup_anon_vma_name(struct vm_area_struct *orig_vma,
> >  				     struct vm_area_struct *new_vma)
> >  {
> >  	struct anon_vma_name *anon_name = anon_vma_name(orig_vma);
> > -
> > -	if (anon_name)
> > -		new_vma->anon_name = anon_vma_name_reuse(anon_name);
> > +	struct anon_vma_name *new_name;
> > +
> > +	if (anon_name) {
> > +		new_name = anon_vma_name_reuse(anon_name);
> > +		if (new_name)
> > +			new_vma->anon_name = new_name;
> > +		else
> > +			WARN_ON_ONCE(1);
>
> Triggering a warning when an allocation fails? Certainly not.

It's pleasing to reply independently and see that we've reached the same
conclusions here :P

I mean, yeah agreed obviously!

>
> --
> Cheers,
>
> David

Cheers, Lorenzo