Re: For review: seccomp_user_notif(2) manual page

From: Sargun Dhillon <sargun@sargun.me>
To: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
Cc: Tycho Andersen <tycho@tycho.pizza>,
	Kees Cook <keescook@chromium.org>,
	Christian Brauner <christian@brauner.io>,
	linux-man <linux-man@vger.kernel.org>,
	lkml <linux-kernel@vger.kernel.org>,
	Aleksa Sarai <cyphar@cyphar.com>, Jann Horn <jannh@google.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Will Drewry <wad@chromium.org>,
	bpf@vger.kernel.org, Song Liu <songliubraving@fb.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andy Lutomirski <luto@amacapital.net>,
	Linux Containers <containers@lists.linux-foundation.org>,
	Giuseppe Scrivano <gscrivan@redhat.com>,
	Robert Sesek <rsesek@google.com>
Subject: Re: For review: seccomp_user_notif(2) manual page
Date: Thu, 1 Oct 2020 14:06:10 -0700	[thread overview]
Message-ID: <CAMp4zn9XA-z_6UKvWkFh_U2wPRjZF3=QvrXX7EikO5AEovCWBA@mail.gmail.com> (raw)
In-Reply-To: <45f07f17-18b6-d187-0914-6f341fe90857@gmail.com>

On Wed, Sep 30, 2020 at 4:07 AM Michael Kerrisk (man-pages)
<mtk.manpages@gmail.com> wrote:
>
> Hi Tycho, Sargun (and all),
>
> I knew it would be a big ask, but below is kind of the manual page
> I was hoping you might write [1] for the seccomp user-space notification
> mechanism. Since you didn't (and because 5.9 adds various new pieces
> such as SECCOMP_ADDFD_FLAG_SETFD and SECCOMP_IOCTL_NOTIF_ADDFD
> that also will need documenting [2]), I did :-). But of course I may
> have made mistakes...
>
> I've shown the rendered version of the page below, and would love
> to receive review comments from you and others, and acks, etc.
>
> There are a few FIXMEs sprinkled into the page, including one
> that relates to what appears to me to be a misdesign (possibly
> fixable) in the operation of the SECCOMP_IOCTL_NOTIF_RECV
> operation. I would be especially interested in feedback on that
> FIXME, and also of course the other FIXMEs.
>
> The page includes an extensive (albeit slightly contrived)
> example program, and I would be happy also to receive comments
> on that program.
>
> The page source currently sits in a branch (along with the text
> that you sent me for the seccomp(2) page) at
> https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/log/?h=seccomp_user_notif
>
> Thanks,
>
> Michael
>
> [1] https://lore.kernel.org/linux-man/2cea5fec-e73e-5749-18af-15c35a4bd23c@gmail.com/#t
> [2] Sargun, can you prepare something on SECCOMP_ADDFD_FLAG_SETFD
>     and SECCOMP_IOCTL_NOTIF_ADDFD to be added to this page?
>
> ====
>
> --
> Michael Kerrisk
> Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
> Linux/UNIX System Programming Training: http://man7.org/training/

Should we consider the SECCOMP_GET_NOTIF_SIZES dance to be "deprecated" at
this point, given that the extensible ioctl mechanism works? If we add
new fields to the
seccomp datastructures, we would move them from fixed-size ioctls, to
variable sized
ioctls that encode the datastructure size / length?

-- This is mostly a question for Kees and Tycho.