Re: [PATCH 1/1] mm: fix vma->anon_name memory leak for anonymous shmem VMAs

[Suren Baghdasaryan]

On Mon, Jan 2, 2023 at 4:00 AM David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> On 28.12.22 20:42, Suren Baghdasaryan wrote:
> > free_anon_vma_name() is missing a check for anonymous shmem VMA which
> > leads to a memory leak due to refcount not being dropped. Fix this by
> > adding the missing check.
> >
> > Fixes: d09e8ca6cb93 ("mm: anonymous shared memory naming")
> > Reported-by: syzbot+91edf9178386a07d06a7@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> > ---
> >   include/linux/mm_inline.h | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
> > index e8ed225d8f7c..d650ca2c5d29 100644
> > --- a/include/linux/mm_inline.h
> > +++ b/include/linux/mm_inline.h
> > @@ -413,7 +413,7 @@ static inline void free_anon_vma_name(struct vm_area_struct *vma)
> >        * Not using anon_vma_name because it generates a warning if mmap_lock
> >        * is not held, which might be the case here.
> >        */
> > -     if (!vma->vm_file)
> > +     if (!vma->vm_file || vma_is_anon_shmem(vma))
> >               anon_vma_name_put(vma->anon_name);
>
> Wouldn't it be me more consistent to check for "vma->anon_name"?
>
> That's what dup_anon_vma_name() checks. And it's safe now because
> anon_name is no longer overloaded in vm_area_struct.

Thanks for the suggestion, David. Yes, with the recent change that
does not overload anon_name, checking for "vma->anon_name" would be
simpler. I think we can also drop anon_vma_name() function now
(https://elixir.bootlin.com/linux/v6.2-rc2/source/mm/madvise.c#L94)
since vma->anon_name does not depend on vma->vm_file anymore, remove
the last part of this comment:
https://elixir.bootlin.com/linux/v6.2-rc2/source/include/linux/mm_types.h#L584
and use vma->anon_name directly going forward. If all that sounds
good, I'll post a separate patch implementing all these changes.
So, for this patch I would suggest keeping it as is because
functionally it is correct and will change this check along with other
corrections I mentioned above in a separate patch. Does that sound
good?


-     if (!vma->vm_file)
+     if (!vma->vm_file || vma_is_anon_shmem(vma))

>
> --
> Thanks,
>
> David / dhildenb
>