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From:   valdis.kletnieks@vt.edu
To:     "Joel Fernandes (Google)" <joel@joelfernandes.org>
Cc:     linux-kernel@vger.kernel.org, kernel-team@android.com,
        jreck@google.com, john.stultz@linaro.org, tkjos@google.com,
        gregkh@linuxfoundation.org, hch@infradead.org,
        Al Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>, dancol@google.com,
        "J. Bruce Fields" <bfields@fieldses.org>,
        Jeff Layton <jlayton@kernel.org>,
        linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org,
        linux-mm@kvack.org, marcandre.lureau@redhat.com,
        Mike Kravetz <mike.kravetz@oracle.com>, minchan@kernel.org,
        Shuah Khan <shuah@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH v3 1/2] mm: Add an F_SEAL_FUTURE_WRITE seal to memfd
In-Reply-To: <20181018065908.254389-1-joel@joelfernandes.org>
References: <20181018065908.254389-1-joel@joelfernandes.org>
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Date:   Fri, 19 Oct 2018 13:32:02 -0400
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On Wed, 17 Oct 2018 23:59:07 -0700, "Joel Fernandes (Google)" said:
> This usecase cannot be implemented with the existing F_SEAL_WRITE seal.
> To support the usecase, this patch adds a new F_SEAL_FUTURE_WRITE seal
> which prevents any future mmap and write syscalls from succeeding while
> keeping the existing mmap active. The following program shows the seal
> working in action:

What is supposed to happen if some other process has an already existing R/W
mmap of the region?  (For that matter, the test program doesn't seem to
actually test that the existing mmap region remains writable?)


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