Re: [PATCH] mm/mincore: allow for making sys_mincore() privileged

[Linus Torvalds]

On Thu, Jan 24, 2019 at 12:12 PM Jiri Kosina <jikos@xxxxxxxxxx> wrote:
>
> >
> > I think the "test vm_file" thing may be unnecessary, because a
> > non-anonymous mapping should always have a file pointer and an inode.
> > But I could  imagine some odd case (vdso mapping, anyone?) that
> > doesn't have a vm_file, but also isn't anonymous.
>
> Hmm, good point.
>
> So dropping the 'vma->vm_file' test and checking whether given vma is
> special mapping should hopefully provide the desired semantics, shouldn't
> it?

Maybe. But on the whole I think it would  be simpler and more
straightforward to just instead add a vm_file test for the
inode_permission() case. That way you at least know that you aren't
following a NULL pointer.

If the file then turns out to be some special thing, it doesn't really
_matter_, I think. It won't have anything in the page cache etc, but
the code should "work".

             Linus