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Date:   Thu, 7 Nov 2019 21:06:14 -0500
From:   Joel Fernandes <joel@joelfernandes.org>
To:     Andrew Morton <akpm@linux-foundation.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: <20191108020614.GA99567@google.com>
References: <20191107195355.80608-1-joel@joelfernandes.org>
 <20191107170023.0695732bb67eb80acd4caee5@linux-foundation.org>
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On Thu, Nov 07, 2019 at 05:00:23PM -0800, Andrew Morton wrote:
> 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?

Yes, it should be. The F_SEAL_FUTURE_WRITE feature was introduced in v5.1 so
v5.3.x stable kernels would need a backport. I can submit a backport tomorrow
unless we are Ok with stable automatically picking it up (I believe the
stable folks "auto select" fixes which should detect this is a fix since I
have said it is a fix in the subject line).

thanks,

 - Joel