netdev - Re: [PATCH net-next v6 1/3] scm: add SO_PASSPIDFD and SCM

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Date: Wed, 24 May 2023 11:47:50 +0100
From: Luca Boccassi <bluca@...ian.org>
To: Aleksandr Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
Cc: Jakub Kicinski <kuba@...nel.org>, Christian Brauner <brauner@...nel.org>, davem@...emloft.net, 
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org, 
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, 
	Leon Romanovsky <leon@...nel.org>, David Ahern <dsahern@...nel.org>, Arnd Bergmann <arnd@...db.de>, 
	Kees Cook <keescook@...omium.org>, Kuniyuki Iwashima <kuniyu@...zon.com>, 
	Lennart Poettering <mzxreary@...inter.de>, linux-arch@...r.kernel.org
Subject: Re: [PATCH net-next v6 1/3] scm: add SO_PASSPIDFD and SCM_PIDFD

On Wed, 24 May 2023 at 11:43, Aleksandr Mikhalitsyn
<aleksandr.mikhalitsyn@...onical.com> wrote:
>
> On Tue, May 23, 2023 at 11:08 PM Jakub Kicinski <kuba@...nel.org> wrote:
> >
> > On Tue, 23 May 2023 11:44:01 +0100 Luca Boccassi wrote:
> > > > I really would like to avoid that because it will just mean that someone
> > > > else will abuse that function and then make an argument why we should
> > > > export the other function.
> > > >
> > > > I think it would be ok if we required that unix support is built in
> > > > because it's not unprecedented either and we're not breaking anything.
> > > > Bpf has the same requirement:
> > > >
> > > >   #if IS_BUILTIN(CONFIG_UNIX) && defined(CONFIG_BPF_SYSCALL)
> > > >   struct bpf_unix_iter_state {
> > > >           struct seq_net_private p;
> > > >           unsigned int cur_sk;
> > > >           unsigned int end_sk;
> > > >           unsigned int max_sk;
> > > >           struct sock **batch;
> > > >           bool st_bucket_done;
> > > >   };
> > > >
> > > > and
> > > >
> > > >   #if IS_BUILTIN(CONFIG_UNIX) && defined(CONFIG_BPF_SYSCALL) && defined(CONFIG_PROC_FS)
> > > >   DEFINE_BPF_ITER_FUNC(unix, struct bpf_iter_meta *meta,
> > > >                        struct unix_sock *unix_sk, uid_t uid)
> >
> > Don't think we should bring BPF into arguments about uAPI consistency :S
> >
> > > Some data points: Debian, Ubuntu, Fedora, RHEL, CentOS, Archlinux all
> > > ship with CONFIG_UNIX=y, so a missing SCM_PIDFD in unlikely to have a
> > > widespread impact, and if it does, it might encourage someone to
> > > review their kconfig.
> >
> > IDK how you can argue that everyone sets UNIX to =y so hiding SCM_PIDFD
> > is fine and at the same time not be okay with making UNIX a bool :S
> >
> > > As mentioned on the v5 thread, we are waiting for this API to get the
> > > userspace side sorted (systemd/dbus/dbus-broker/polkit), so I'd be
> > > really grateful if we could start with the simplest and most
> > > conservative approach (which seems to be the current one in v6 to me),
> > > and then eventually later decide whether to export more functions, or
> > > to deprecate CONFIG_UNIX=m, or something else entirely, as that
> > > doesn't really affect the shape of the UAPI, just the details of its
> > > availability. Thank you.
> >
> > Just throw in a patch to make UNIX a bool and stop arguing then.
>
> Dear Jakub,
>
> Thanks for your attention to these patch series!
>
> I'm ready to prepare/send a patch to make CONFIG_UNIX bool.
>
> I will send SO_PEERPIDFD as an independent patch too, because it
> doesn't require this change with CONFIG_UNIX
> and we can avoid waiting until CONFIG_UNIX change will be merged.
> I've a feeling that the discussion around making CONFIG_UNIX  to be a
> boolean won't be easy and fast ;-)

Thank you, that sounds great to me, I can start using SO_PEERPIDFD
independently of SCM_PIDFD, there's no hard dependency between the
two.

Kind regards,
Luca Boccassi