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

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Date: Thu, 22 Feb 2024 13:00:05 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Qi Zheng <zhengqi.arch@...edance.com>
Cc: aarcange@...hat.com, surenb@...gle.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, 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?