linux-kernel - Re: [PATCH v2 0/2] mm/memfd: add ioctl(MEMFD_CHECK_IF

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Message-ID: <87h6o4z5dn.fsf@meer.lwn.net>
Date:   Fri, 08 Sep 2023 16:07:00 -0600
From:   Jonathan Corbet <corbet@....net>
To:     Michał Cłapiński <mclapinski@...gle.com>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>, Shuah Khan <shuah@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>, Yi Liu <yi.l.liu@...el.com>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Steve French <stfrench@...rosoft.com>,
        Simon Ser <contact@...rsion.fr>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Marc Dionne <marc.dionne@...istor.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        David Howells <dhowells@...hat.com>,
        Luca Vizzarro <Luca.Vizzarro@....com>,
        Jeff Xu <jeffxu@...gle.com>, Aleksa Sarai <cyphar@...har.com>,
        Kees Cook <keescook@...omium.org>,
        Daniel Verkamp <dverkamp@...omium.org>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 0/2] mm/memfd: add ioctl(MEMFD_CHECK_IF_ORIGINAL)

Michał Cłapiński <mclapinski@...gle.com> writes:

> On Fri, Sep 8, 2023 at 10:34 PM Jonathan Corbet <corbet@....net> wrote:
>> Given that the two file descriptors are otherwise indistinguishable,
>> might a better fix be to make them indistinguishable in this regard as
>> well?  Is there a good reason why the second fd doesn't become
>> exec()able in this scenario and, if not, perhaps that behavior could be
>> changed instead?
>
> It probably could be changed, yes. But I'm worried that would be
> broadening the bug that is the exec()ability of memfds. AFAIK no other
> fd that is opened as writable can be exec()ed. If maintainers would
> prefer this, I could do this.

I'm not convinced that perpetuating the behavior and adding an ioctl()
workaround would be better than that; it seems to me that consistency
would be better.  But I don't have any real say in that matter, of
course; I'm curious what others think.

Thanks,

jon