Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Thu, 7 Nov 2019 19:25:28 -0800
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Joel Fernandes <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: <20191107192528.0c22e8e122a04d4f8d29c5eb@linux-foundation.org>
In-Reply-To: <20191108020614.GA99567@google.com>
References: <20191107195355.80608-1-joel@joelfernandes.org>
        <20191107170023.0695732bb67eb80acd4caee5@linux-foundation.org>
        <20191108020614.GA99567@google.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, 7 Nov 2019 21:06:14 -0500 Joel Fernandes <joel@joelfernandes.org> wrote:

> 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.

I added

Fixes: ab3948f58ff84 ("mm/memfd: add an F_SEAL_FUTURE_WRITE seal to memfd")
Cc: <stable@vger.kernel.org>

> 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).

The Cc:stable tag should trigger the appropriate actions, assisted by
the Fixes:.  I doubt if "fix" in the Subject has much effect.