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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sat, 30 Mar 2019 09:16:46 -0700
Message-ID: <CAHk-=wjka0W1g3asQp2H=5ot=kkS-Mp+Cx6KHr0rNkGFfCOLYA@mail.gmail.com>
Subject: Re: [PATCH v2 0/5] pid: add pidfd_open()
To:     Daniel Colascione <dancol@google.com>
Cc:     Christian Brauner <christian@brauner.io>,
        Jann Horn <jannh@google.com>,
        Andrew Lutomirski <luto@kernel.org>,
        David Howells <dhowells@redhat.com>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        Linux API <linux-api@vger.kernel.org>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
        Kees Cook <keescook@chromium.org>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Michael Kerrisk-manpages <mtk.manpages@gmail.com>,
        Jonathan Kowalski <bl0pbl33p@gmail.com>,
        "Dmitry V. Levin" <ldv@altlinux.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Nagarathnam Muthusamy <nagarathnam.muthusamy@oracle.com>,
        Aleksa Sarai <cyphar@cyphar.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Joel Fernandes <joel@joelfernandes.org>
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On Sat, Mar 30, 2019 at 9:11 AM Daniel Colascione <dancol@google.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