Re: [PATCH v1] mm/gup: fix FOLL_FORCE COW security issue and remove FOLL_COW

Linus Torvalds
2022-08-09T19:07:44Z

On Mon, Aug 8, 2022 at 12:32 AM David Hildenbrand <david@redhat.com> wrote:
>
> For example, a write() via /proc/self/mem to a uffd-wp-protected range has
> to fail instead of silently granting write access and bypassing the
> userspace fault handler.

This, btw, just makes me go "uffd-wp is broken garbage" once more.

It also makes me go "if uffd-wp can disallow ptrace writes, then why
doesn't regular write protect do it"?

IOW, I don't think the patch is wrong (apart from the VM_BUG_ON's that
absolutely must go away), but I get the strong feelign that we instead
should try to get rid of FOLL_FORCE entirely.

If some other user action can stop FOLL_FORCE anyway, then why do we
support it at all?

Linus