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Date:   Mon, 1 Apr 2019 00:33:56 +0200
From:   Christian Brauner <>
To:     Linus Torvalds <>
Cc:     Andy Lutomirski <>,
        Daniel Colascione <>,
        Jann Horn <>,
        Andrew Lutomirski <>,
        David Howells <>,
        "Serge E. Hallyn" <>,
        Linux API <>,
        Linux List Kernel Mailing <>,
        Arnd Bergmann <>,
        "Eric W. Biederman" <>,
        Konstantin Khlebnikov <>,
        Kees Cook <>,
        Alexey Dobriyan <>,
        Thomas Gleixner <>,
        Michael Kerrisk-manpages <>,
        Jonathan Kowalski <>,
        "Dmitry V. Levin" <>,
        Andrew Morton <>,
        Oleg Nesterov <>,
        Nagarathnam Muthusamy <>,
        Aleksa Sarai <>,
        Al Viro <>,
        Joel Fernandes <>
Subject: Re: [PATCH v2 0/5] pid: add pidfd_open()

On Sun, Mar 31, 2019 at 03:16:47PM -0700, Linus Torvalds wrote:
> On Sun, Mar 31, 2019 at 3:03 PM Christian Brauner <> wrote:
> >
> > Thanks for the input. The problem Jann and I saw with this is that it
> > would be awkward to have the kernel open a file in some procfs instance,
> > since then userspace would have to specify which procfs instance the fd
> > should come from.
> I would actually suggest we just make the rules be that the
> pidfd_open() always return the internal /proc entry regardless of any
> mount-point (or any "hidepid") but also suggest that exactly *because*
> it gives you visibility into the target pid, you'd basically require
> the strictest kind of control of the process you're trying to get the
> pidfd of.
> Ie likely something along the lines of
>         ptrace_may_access(task, PTRACE_MODE_ATTACH_REALCREDS)

I can live with that but I would like to hear what Jann thinks too if
that's ok.


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