linux-kernel - Re: [PATCH v2 0/5] pid: add pidfd

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Message-ID: <CAHk-=whcA0kAWGqet9oJdyttjhP7J4PcU2Ly=n_Qyo6rMJNxRg@mail.gmail.com>
Date:   Sat, 30 Mar 2019 09:24:23 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Christian Brauner <christian@...uner.io>
Cc:     Jann Horn <jannh@...gle.com>, Andrew Lutomirski <luto@...nel.org>,
        David Howells <dhowells@...hat.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Linux API <linux-api@...r.kernel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        Kees Cook <keescook@...omium.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Michael Kerrisk-manpages <mtk.manpages@...il.com>,
        Jonathan Kowalski <bl0pbl33p@...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 v2 0/5] pid: add pidfd_open()

On Sat, Mar 30, 2019 at 9:19 AM Christian Brauner <christian@...uner.io> wrote:
>
> From pure API perspective that's all I care about: independence of procfs.
> Once we have pidfd_open() we can cleanly signal threads etc.

But "independence from procfs" means that you damn well don't then do
"oh, now I have a pidfd, I want to turn it into a /proc fd and then
munge around there".

So I'm literally saying that it had better really *be* independent
from /proc. It is the standalone version, but it's most definitely
also the version that doesn't then give you secret access to /proc.

And it weorries me a lot that people are trying to play these kinds of
games. I'm just seeing some android patch that adds this horror and
then starts using it.

                      Linus