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

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Date:   Sat, 30 Mar 2019 09:11:22 -0700
From:   Daniel Colascione <dancol@...gle.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
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 9:09 AM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Fri, Mar 29, 2019 at 8:54 AM Christian Brauner <christian@...uner.io> wrote:
> >
> > /* Introduction */
> > This adds the pidfd_open() syscall.
> > pidfd_open() allows to retrieve file descriptors for a given pid. This
> > includes both file descriptors for processes and file descriptors for
> > threads.
>
> I'm ok with the pidfd_open() call to just get a pidfd, but that
> "pidfd_to_profs()" needs to go away.
>
> If you want to open the /proc/<pid>/status file, then just do that.
> This whole "do one and convert to the other" needs to die. No, no, no.

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?