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Subject: Re: RFC: on adding new CLONE_* flags [WAS Re: [PATCH 0/4] clone: add
 CLONE_PIDFD]
To:     Christian Brauner <christian@brauner.io>
Cc:     Andy Lutomirski <luto@kernel.org>,
        Aleksa Sarai <cyphar@cyphar.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
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        David Howells <dhowells@redhat.com>,
        Linux API <linux-api@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        Arnd Bergmann <arnd@arndb.de>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Kees Cook <keescook@chromium.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Daniel Colascione <dancol@google.com>
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 <20190417125422.bhyrmzom4kwuenwm@brauner.io>
From:   "Enrico Weigelt, metux IT consult" <lkml@metux.net>
Organization: metux IT consult
Message-ID: <ac16b51d-3bcf-45ff-aa57-85d5da7224c2@metux.net>
Date:   Thu, 18 Apr 2019 17:46:47 +0200
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On 17.04.19 14:54, Christian Brauner wrote:

>> Ah, that is a cool thing !>> I suppose that also works across namespaces ?> > Yes, it should. If
you hand off the pidfd to another pidns (e.g. via SCM> credentials) for
example.
I thought about things like sending the pidfd via unix socket.
It would be really cool if the receiving process could then control
the referred process (eg. send signals), even if it's in a different
pidns.

>> What other things can be done via pidfd ?
> 
> Very basic things right now and until CLONE_PIDFD is accepted (possibly
> for 5.2) we won't enable any more features.
> I'm not a fan of wild speculations and grand schemes that then don't
> come to fruition. :) Right now it's about focussing on somewhat cleanly
> covering the basics. Coming to a consensus there was hard enough. We
> have no intention in making this more complex right now as it needs to
> be.

IMHO, it would be good if it would support all operations that now can
be done via numerical PID, and w/ the permissions of the process who
created that pidfd. Certainly, that would also need some lockdown
mechanism, so the creating process can define what the holder of the
fd can actually do.

--mtx

-- 
Enrico Weigelt, metux IT consult
Free software and Linux embedded engineering
info@metux.net -- +49-151-27565287