linux-kernel - Re: [PATCH] mm: userfaultfd: fix unexpected change to src_folio when UFFDIO

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Message-ID: <CAJuCfpHoxAZvRx2VN+SzsjefB5demhk5OV_wPe8JYnsejgA91w@mail.gmail.com>
Date: Thu, 22 Feb 2024 13:56:44 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Qi Zheng <zhengqi.arch@...edance.com>, aarcange@...hat.com, david@...hat.com, 
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: userfaultfd: fix unexpected change to src_folio when
 UFFDIO_MOVE fails

On Thu, Feb 22, 2024 at 1:00 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Thu, 22 Feb 2024 16:08:15 +0800 Qi Zheng <zhengqi.arch@...edance.com> 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?