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

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Message-ID: <20230523140844.5895d645@kernel.org>
Date:   Tue, 23 May 2023 14:08:44 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Luca Boccassi <bluca@...ian.org>
Cc:     Christian Brauner <brauner@...nel.org>,
        Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>,
        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 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.