Re: [PATCH v2 0/2] mm/memfd: add ioctl(MEMFD_CHECK_IF_ORIGINAL)

From: Jonathan Corbet <corbet@lwn.net>
To: "Michał Cłapiński" <mclapinski@google.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>,
	Muchun Song <muchun.song@linux.dev>,
	Andrew Morton <akpm@linux-foundation.org>,
	Hugh Dickins <hughd@google.com>, Shuah Khan <shuah@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Arnd Bergmann <arnd@arndb.de>, Yi Liu <yi.l.liu@intel.com>,
	Dominik Brodowski <linux@dominikbrodowski.net>,
	Hans Verkuil <hverkuil-cisco@xs4all.nl>,
	Steve French <stfrench@microsoft.com>,
	Simon Ser <contact@emersion.fr>, Jason Gunthorpe <jgg@ziepe.ca>,
	Marc Dionne <marc.dionne@auristor.com>,
	Jiri Slaby <jirislaby@kernel.org>,
	David Howells <dhowells@redhat.com>,
	Luca Vizzarro <Luca.Vizzarro@arm.com>,
	Jeff Xu <jeffxu@google.com>, Aleksa Sarai <cyphar@cyphar.com>,
	Kees Cook <keescook@chromium.org>,
	Daniel Verkamp <dverkamp@chromium.org>,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v2 0/2] mm/memfd: add ioctl(MEMFD_CHECK_IF_ORIGINAL)
Date: Fri, 08 Sep 2023 16:07:00 -0600	[thread overview]
Message-ID: <87h6o4z5dn.fsf@meer.lwn.net> (raw)
In-Reply-To: <CAAi7L5f1f3gHGr_8cCv2jW2Q5pjL9bpDD_4zrpXjXkoRmu95fg@mail.gmail.com>

Michał Cłapiński <mclapinski@google.com> writes:

> On Fri, Sep 8, 2023 at 10:34 PM Jonathan Corbet <corbet@lwn.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