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Date:   Thu, 7 Nov 2019 17:00:23 -0800
From:   Andrew Morton <akpm@linux-foundation.org>
To:     "Joel Fernandes (Google)" <joel@joelfernandes.org>
Cc:     linux-kernel@vger.kernel.org,
        Nicolas Geoffray <ngeoffray@google.com>,
        kernel-team@android.com, Hugh Dickins <hughd@google.com>,
        linux-kselftest@vger.kernel.org, linux-mm@kvack.org,
        Shuah Khan <shuah@kernel.org>
Subject: Re: [PATCH 1/2] memfd: Fix COW issue on MAP_PRIVATE and
 F_SEAL_FUTURE_WRITE mappings
Message-Id: <20191107170023.0695732bb67eb80acd4caee5@linux-foundation.org>
In-Reply-To: <20191107195355.80608-1-joel@joelfernandes.org>
References: <20191107195355.80608-1-joel@joelfernandes.org>
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On Thu,  7 Nov 2019 14:53:54 -0500 "Joel Fernandes (Google)" <joel@joelfernandes.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?