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From: Joel Fernandes <joel@joelfernandes.org>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	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
Date: Fri, 8 Nov 2019 10:34:10 -0500
Message-ID: <20191108153410.GB99567@google.com> (raw)
In-Reply-To: <20191108063715.GA513315@kroah.com>

On Fri, Nov 08, 2019 at 07:37:15AM +0100, Greg KH wrote:
> On Thu, Nov 07, 2019 at 09:06:14PM -0500, Joel Fernandes 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. 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).
> 
> Never rely on "auto select" to pick up a patch for stable if you already
> know it should go to stable.  Just mark it as such, or tell stable@vger
> after the fact.

Sure, agreed.

Thanks Andrew for adding the tags!

thanks,

 - Joel


  reply index

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-07 19:53 Joel Fernandes (Google)
2019-11-07 19:53 ` [PATCH 2/2] memfd: Add test for COW " Joel Fernandes (Google)
2019-11-08  1:00 ` [PATCH 1/2] memfd: Fix COW issue " Andrew Morton
2019-11-08  2:06   ` Joel Fernandes
2019-11-08  3:25     ` Andrew Morton
2019-11-08  6:37     ` Greg KH
2019-11-08 15:34       ` Joel Fernandes [this message]
2019-11-08  6:33 ` Christoph Hellwig
2019-11-08 15:35   ` Joel Fernandes

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