linux-kernel - Re: [PATCH v3 1/2] mm: Add an F_SEAL_FUTURE

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Message-ID: <42922.1539970322@turing-police.cc.vt.edu>
Date:   Fri, 19 Oct 2018 13:32:02 -0400
From:   valdis.kletnieks@...edu
To:     "Joel Fernandes (Google)" <joel@...lfernandes.org>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        jreck@...gle.com, john.stultz@...aro.org, tkjos@...gle.com,
        gregkh@...uxfoundation.org, hch@...radead.org,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>, dancol@...gle.com,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Jeff Layton <jlayton@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-mm@...ck.org, marcandre.lureau@...hat.com,
        Mike Kravetz <mike.kravetz@...cle.com>, minchan@...nel.org,
        Shuah Khan <shuah@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v3 1/2] mm: Add an F_SEAL_FUTURE_WRITE seal to memfd

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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