From: Kees Cook <keescook@chromium.org>
To: "Michał Cłapiński" <mclapinski@google.com>
Cc: Christian Brauner <brauner@kernel.org>,
Jeff Layton <jlayton@kernel.org>,
Chuck Lever <chuck.lever@oracle.com>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Shuah Khan <shuah@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Jeff Xu <jeffxu@google.com>, Aleksa Sarai <cyphar@cyphar.com>,
Daniel Verkamp <dverkamp@chromium.org>,
Marc Dionne <marc.dionne@auristor.com>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-kselftest@vger.kernel.org
Subject: Re: [PATCH 1/2] fcntl: add fcntl(F_CHECK_ORIGINAL_MEMFD)
Date: Fri, 1 Sep 2023 11:34:32 -0700 [thread overview]
Message-ID: <202309011133.10D66D0785@keescook> (raw)
In-Reply-To: <CAAi7L5f1KYrAyCYLzUN0dSy6xuQCGcC7SQML4+KUdxnQ6RaFfg@mail.gmail.com>
On Fri, Sep 01, 2023 at 04:50:53PM +0200, Michał Cłapiński wrote:
> On Fri, Sep 1, 2023 at 2:56 PM Christian Brauner <brauner@kernel.org> wrote:
> >
> > On Thu, Aug 31, 2023 at 10:36:46PM +0200, Michal Clapinski wrote:
> > > Add a way to check if an fd points to the memfd's original open fd
> > > (the one created by memfd_create).
> > > Useful because only the original open fd can be both writable and
> > > executable.
> > >
> > > Signed-off-by: Michal Clapinski <mclapinski@google.com>
> > > ---
> > > fs/fcntl.c | 3 +++
> > > include/uapi/linux/fcntl.h | 9 +++++++++
> > > 2 files changed, 12 insertions(+)
> > >
> > > diff --git a/fs/fcntl.c b/fs/fcntl.c
> > > index e871009f6c88..301527e07a4d 100644
> > > --- a/fs/fcntl.c
> > > +++ b/fs/fcntl.c
> > > @@ -419,6 +419,9 @@ static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
> > > case F_SET_RW_HINT:
> > > err = fcntl_rw_hint(filp, cmd, arg);
> > > break;
> > > + case F_CHECK_ORIGINAL_MEMFD:
> > > + err = !(filp->f_mode & FMODE_WRITER);
> > > + break;
> >
> > Honestly, make this an ioctl on memfds. This is so specific that it
> > really doesn't belong into fcntl().
>
> I've never touched ioctls but if I'm correct, I can't just add it to
> memfd. I would have to add it to the underlying fs, so hugetlbfs and
> shmem (which I think can be defined as ramfs so also there). File
> sealing fcntl is already memfd specific. Are you sure ioctl will be a
> better idea?
Does this check "mean" anything for other files? Because if it's
generically useful (and got renamed) it maybe would be right for
fcntl...
--
Kees Cook
next prev parent reply other threads:[~2023-09-01 18:34 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-31 20:36 [PATCH 0/2] fcntl: add fcntl(F_CHECK_ORIGINAL_MEMFD) Michal Clapinski
2023-08-31 20:36 ` [PATCH 1/2] " Michal Clapinski
2023-09-01 12:56 ` Christian Brauner
2023-09-01 14:50 ` Michał Cłapiński
2023-09-01 18:34 ` Kees Cook [this message]
2023-09-04 7:29 ` Christian Brauner
2023-09-04 17:57 ` Michał Cłapiński
2023-09-05 8:37 ` Christian Brauner
2023-08-31 20:36 ` [PATCH 2/2] selftests: test fcntl(F_CHECK_ORIGINAL_MEMFD) Michal Clapinski
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