Re: [PATCH -next] mm/memory: fix null pointer dereference in fault_dirty_shared_page

[Lorenzo Stoakes]

On Mon, Jul 07, 2025 at 02:27:01PM +0200, David Hildenbrand wrote:
> IIRC, MAP_ANON |MAP_SHARED would have done a shmem_zero_setup().
>
> mm/mmap.c still has the comment "mmap_region() will call shmem_zero_setup()
> to create a file".

Correct.

>
> I think this was moved to __mmap_new_vma().
>
> Is there any (error) path where we could not call that by accident?

No.

Shared means there's a file.

This also would mean we've been kernel NULL pointer dereferencing since
2019 btw when this change was made. I don't recall the reports... :>)

I think people get confused because MAP_SHARED | MAP_ANON makes people
think there won't be a file.

Our terminology sucks...

>
> --
> Cheers,
>
> David / dhildenb
>