Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <20190329155425.26059-1-christian@brauner.io> <CAHk-=wjq4dTPcz-qsvhpm5F42SDHCoqEWv1V=rs_kt6MC=ZThA@mail.gmail.com>
In-Reply-To: <CAHk-=wjq4dTPcz-qsvhpm5F42SDHCoqEWv1V=rs_kt6MC=ZThA@mail.gmail.com>
From:   Daniel Colascione <dancol@google.com>
Date:   Sat, 30 Mar 2019 09:11:22 -0700
Message-ID: <CAKOZueuDWWYtg9gUpUgTG2k-gVPE1KBEkstr5eP=FC2EzdmaoA@mail.gmail.com>
Subject: Re: [PATCH v2 0/5] pid: add pidfd_open()
To:     Linus Torvalds <torvalds@linux-foundation.org>
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>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Sat, Mar 30, 2019 at 9:09 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Fri, Mar 29, 2019 at 8:54 AM Christian Brauner <christian@brauner.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?