Re: [PATCH] mm: userfaultfd: fix unexpected change to src_folio when UFFDIO_MOVE fails

[Suren Baghdasaryan]

On Thu, Feb 22, 2024 at 1:00 PM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> On Thu, 22 Feb 2024 16:08:15 +0800 Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx> wrote:
>
> > After ptep_clear_flush(), if we find that src_folio is pinned we will fail
> > UFFDIO_MOVE and put src_folio back to src_pte entry, but the change to
> > src_folio->{mapping,index} is not restored in this process. This is not
> > what we expected, so fix it.
> >
> > Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
>
> What are the expected worst-case userspace-visible runtime effects of
> this flaw?

It can cause rmap for that page to be invalid. I guess memory
corruption might be the visible effect?