linux-kernel - Re: [PATCH 1/2] memfd: Fix COW issue on MAP_PRIVATE and F_SEAL_FUTURE

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Message-Id: <20191107170023.0695732bb67eb80acd4caee5@linux-foundation.org>
Date:   Thu, 7 Nov 2019 17:00:23 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     "Joel Fernandes (Google)" <joel@...lfernandes.org>
Cc:     linux-kernel@...r.kernel.org,
        Nicolas Geoffray <ngeoffray@...gle.com>,
        kernel-team@...roid.com, Hugh Dickins <hughd@...gle.com>,
        linux-kselftest@...r.kernel.org, linux-mm@...ck.org,
        Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH 1/2] memfd: Fix COW issue on MAP_PRIVATE and
 F_SEAL_FUTURE_WRITE mappings

On Thu,  7 Nov 2019 14:53:54 -0500 "Joel Fernandes (Google)" <joel@...lfernandes.org> wrote:

> F_SEAL_FUTURE_WRITE has unexpected behavior when used with MAP_PRIVATE:
> A private mapping created after the memfd file that gets sealed with
> F_SEAL_FUTURE_WRITE loses the copy-on-write at fork behavior, meaning
> children and parent share the same memory, even though the mapping is
> private.

That sounds fairly serious.  Should this be backported into -stable kernels?