linux-kernel - Re: [PATCH] userfaultfd: fix mmap_changing checking in mfill_atomic

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Message-Id: <20240118135941.c7795d52881f486aa21aeea8@linux-foundation.org>
Date: Thu, 18 Jan 2024 13:59:41 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Lokesh Gidra <lokeshgidra@...gle.com>
Cc: linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, selinux@...r.kernel.org, surenb@...gle.com,
 kernel-team@...roid.com, aarcange@...hat.com, peterx@...hat.com,
 david@...hat.com, axelrasmussen@...gle.com, bgeffon@...gle.com,
 willy@...radead.org, jannh@...gle.com, kaleshsingh@...gle.com,
 ngeoffray@...gle.com
Subject: Re: [PATCH] userfaultfd: fix mmap_changing checking in
 mfill_atomic_hugetlb

On Wed, 17 Jan 2024 14:37:29 -0800 Lokesh Gidra <lokeshgidra@...gle.com> wrote:

> In mfill_atomic_hugetlb(), mmap_changing isn't being checked
> again if we drop mmap_lock and reacquire it. When the lock is not held,
> mmap_changing could have been incremented. This is also inconsistent
> with the behavior in mfill_atomic().

Thanks. Could you and reviewers please consider

- what might be the userspace-visible runtime effects?

- Should the fix be backported into earlier kernels?

- A suitable Fixes: target?