linux-kernel - Re: [PATCH 2/4] pid: add pidfd

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Date:   Wed, 27 Mar 2019 20:17:14 +0000
From:   Jonathan Kowalski <bl0pbl33p@...il.com>
To:     Christian Brauner <christian@...uner.io>
Cc:     Jann Horn <jannh@...gle.com>,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        Andy Lutomirski <luto@...nel.org>,
        David Howells <dhowells@...hat.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Linux API <linux-api@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Kees Cook <keescook@...omium.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Michael Kerrisk-manpages <mtk.manpages@...il.com>,
        "Dmitry V. Levin" <ldv@...linux.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Nagarathnam Muthusamy <nagarathnam.muthusamy@...cle.com>,
        Aleksa Sarai <cyphar@...har.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Joel Fernandes <joel@...lfernandes.org>,
        Daniel Colascione <dancol@...gle.com>
Subject: Re: [PATCH 2/4] pid: add pidfd_open()

On Wed, Mar 27, 2019 at 7:38 PM Jonathan Kowalski <bl0pbl33p@...il.com> wrote:
>  ...
> ... the process cannot get it out
> of thin air on its own (and you already mentioned it has nothing to do
> with security). What I do worry about is one can use NS_GET_PARENT

disregard this, it works as it should.

> ioctl to get the parent pidns if the owning userns is the same, and
> just passing that gives me back a pidfd for the task. **So, you might
> want to add the constraint that the PID is actually reachable by the
> current task as well, apart from being reachable in the passed in
> namespace.**
>
> Lastly, I also see no need of /proc/<PID> dir fd to pidfd conversion,
> I would even recommend getting rid of that, so we only have one type
> of pidfd, the anon inode one. What is the usecase behind that? It
> would only be needed if you did not have a way to be able to metadata
> access through a pidfd, which would be the case only prior to this
> patch.
>
> I think this would simplify a lot of things, and ioctl_ns(2) is
> probably already the place to do comparison operations and query
> operations on hierarichal namespaces, just adding the relative PID bit
> will make it gain feature parity with translate_pid.