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

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Message-ID: <CAHk-=wjka0W1g3asQp2H=5ot=kkS-Mp+Cx6KHr0rNkGFfCOLYA@mail.gmail.com>
Date:   Sat, 30 Mar 2019 09:16:46 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Daniel Colascione <dancol@...gle.com>
Cc:     Christian Brauner <christian@...uner.io>,
        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>
Subject: Re: [PATCH v2 0/5] pid: add pidfd_open()

On Sat, Mar 30, 2019 at 9:11 AM Daniel Colascione <dancol@...gle.com> wrote:
>
> How do you propose that someone open the /proc/<pid>/status file in a
> race-free manner starting with the result of calling pidfd_open?

CXhrist.

If you want to open a /proc file, then open a /proc file. Don't use
pidfd_open().

Just open /proc/<pid>/

Then you can use openat() to open whatever sub-files you want.

You have two choices: either you use /proc, or you don't. Don't mix the two.

And no, we are *NOT* making pidfd_open() into some "let's expose /proc
even when it's not mounted" horror. Seriously. That's disgusting,
wrong, insecure and stupid.

                           Linus