From: Daniel Colascione <dancol@google.com>
To: Christian Brauner <christian@brauner.io>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Jann Horn <jannh@google.com>,
Joel Fernandes <joel@joelfernandes.org>,
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>
Subject: Re: [PATCH v2 0/5] pid: add pidfd_open()
Date: Sun, 31 Mar 2019 08:21:39 -0700 [thread overview]
Message-ID: <CAKOZues=PUZzKWoL10qiaLXgbDwE0YjygSdf4ZZSZHvOYMO=3w@mail.gmail.com> (raw)
In-Reply-To: <20190331150507.zpyugdvtmr6rgpda@brauner.io>
On Sun, Mar 31, 2019 at 8:05 AM Christian Brauner <christian@brauner.io> wrote:
>
> On Sun, Mar 31, 2019 at 07:52:28AM -0700, Linus Torvalds wrote:
> > On Sat, Mar 30, 2019 at 9:47 PM Jann Horn <jannh@google.com> wrote:
> > >
> > > Sure, given a pidfd_clone() syscall, as long as the parent of the
> > > process is giving you a pidfd for it and you don't have to deal with
> > > grandchildren created by fork() calls outside your control, that
> > > works.
> >
> > Don't do pidfd_clone() and pidfd_wait().
> >
> > Both of those existing system calls already get a "flags" argument.
> > Just make a WPIDFD (for waitid) and CLONE_PIDFD (for clone) bit, and
> > make the existing system calls just take/return a pidfd.
>
> Yes, that's one of the options I was considering but was afraid of
> pitching it because of the very massive opposition I got
> regarding"multiplexers". I'm perfectly happy with doing it this way.
This approach is fine by me, FWIW. I like it more than a general-purpose pidctl.
> Btw, the /proc/<pid> race issue that is mentioned constantly is simply
> avoidable by placing the pid that the pidfd has stashed relative to the
> callers' procfs mount's pid namespace in the pidfd's fdinfo. So there's
> not even a need to really go through /proc/<pid> in the first place. A
> caller wanting to get metadata access and avoid a race with pid
> recycling can then simply do:
>
> int pidfd = pidfd_open(pid, 0);
> int pid = parse_fdinfo("/proc/self/fdinfo/<pidfd>");
> int procpidfd = open("/proc/<pid>", ...);
IMHO, it's worth documenting this procedure in the pidfd man page.
> /* Test if process still exists by sending signal 0 through our pidfd. */
Are you planning on officially documenting this incantation in the
pidfd man page?
> int ret = pidfd_send_signal(pid, 0, NULL, PIDFD_SIGNAL_THREAD);
> if (ret < 0 && errno == ESRCH) {
> /* pid has been recycled and procpidfd refers to another process */
> }
I was going to suggest that WNOHANG also works for this purpose, but
that idea raises another question: normally, you can wait*(2) on a
process only once. Are you imagining waitid on a pidfd succeeding more
than one? ISTM that the pidfd would need to internally store not just
a struct pid, but the exit status as well or some way to get to it.
WARNING: multiple messages have this Message-ID (diff)
From: Daniel Colascione <dancol@google.com>
To: Christian Brauner <christian@brauner.io>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Jann Horn <jannh@google.com>,
Joel Fernandes <joel@joelfernandes.org>,
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
Subject: Re: [PATCH v2 0/5] pid: add pidfd_open()
Date: Sun, 31 Mar 2019 08:21:39 -0700 [thread overview]
Message-ID: <CAKOZues=PUZzKWoL10qiaLXgbDwE0YjygSdf4ZZSZHvOYMO=3w@mail.gmail.com> (raw)
In-Reply-To: <20190331150507.zpyugdvtmr6rgpda@brauner.io>
On Sun, Mar 31, 2019 at 8:05 AM Christian Brauner <christian@brauner.io> wrote:
>
> On Sun, Mar 31, 2019 at 07:52:28AM -0700, Linus Torvalds wrote:
> > On Sat, Mar 30, 2019 at 9:47 PM Jann Horn <jannh@google.com> wrote:
> > >
> > > Sure, given a pidfd_clone() syscall, as long as the parent of the
> > > process is giving you a pidfd for it and you don't have to deal with
> > > grandchildren created by fork() calls outside your control, that
> > > works.
> >
> > Don't do pidfd_clone() and pidfd_wait().
> >
> > Both of those existing system calls already get a "flags" argument.
> > Just make a WPIDFD (for waitid) and CLONE_PIDFD (for clone) bit, and
> > make the existing system calls just take/return a pidfd.
>
> Yes, that's one of the options I was considering but was afraid of
> pitching it because of the very massive opposition I got
> regarding"multiplexers". I'm perfectly happy with doing it this way.
This approach is fine by me, FWIW. I like it more than a general-purpose pidctl.
> Btw, the /proc/<pid> race issue that is mentioned constantly is simply
> avoidable by placing the pid that the pidfd has stashed relative to the
> callers' procfs mount's pid namespace in the pidfd's fdinfo. So there's
> not even a need to really go through /proc/<pid> in the first place. A
> caller wanting to get metadata access and avoid a race with pid
> recycling can then simply do:
>
> int pidfd = pidfd_open(pid, 0);
> int pid = parse_fdinfo("/proc/self/fdinfo/<pidfd>");
> int procpidfd = open("/proc/<pid>", ...);
IMHO, it's worth documenting this procedure in the pidfd man page.
> /* Test if process still exists by sending signal 0 through our pidfd. */
Are you planning on officially documenting this incantation in the
pidfd man page?
> int ret = pidfd_send_signal(pid, 0, NULL, PIDFD_SIGNAL_THREAD);
> if (ret < 0 && errno == ESRCH) {
> /* pid has been recycled and procpidfd refers to another process */
> }
I was going to suggest that WNOHANG also works for this purpose, but
that idea raises another question: normally, you can wait*(2) on a
process only once. Are you imagining waitid on a pidfd succeeding more
than one? ISTM that the pidfd would need to internally store not just
a struct pid, but the exit status as well or some way to get to it.
next prev parent reply other threads:[~2019-03-31 15:21 UTC|newest]
Thread overview: 158+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-29 15:54 [PATCH v2 0/5] pid: add pidfd_open() Christian Brauner
2019-03-29 15:54 ` [PATCH v2 1/5] Make anon_inodes unconditional Christian Brauner
2019-03-29 15:54 ` [PATCH v2 2/5] pid: add pidfd_open() Christian Brauner
2019-03-29 23:45 ` Jann Horn
2019-03-29 23:45 ` Jann Horn
2019-03-29 23:55 ` Christian Brauner
2019-03-29 23:55 ` Christian Brauner
2019-03-30 11:53 ` Jürg Billeter
2019-03-30 14:37 ` Christian Brauner
2019-03-30 14:51 ` Jonathan Kowalski
2019-03-30 14:51 ` Jonathan Kowalski
2019-03-29 15:54 ` [PATCH v2 3/5] signal: support pidfd_open() with pidfd_send_signal() Christian Brauner
2019-03-29 15:54 ` [PATCH v2 4/5] signal: PIDFD_SIGNAL_TID threads via pidfds Christian Brauner
2019-03-30 1:06 ` Jann Horn
2019-03-30 1:06 ` Jann Horn
2019-03-30 1:22 ` Christian Brauner
2019-03-30 1:22 ` Christian Brauner
2019-03-30 1:34 ` Christian Brauner
2019-03-30 1:34 ` Christian Brauner
2019-03-30 1:42 ` Christian Brauner
2019-03-30 1:42 ` Christian Brauner
2019-03-29 15:54 ` [PATCH v2 5/5] tests: add pidfd_open() tests Christian Brauner
2019-03-30 16:09 ` [PATCH v2 0/5] pid: add pidfd_open() Linus Torvalds
2019-03-30 16:09 ` Linus Torvalds
2019-03-30 16:11 ` Daniel Colascione
2019-03-30 16:11 ` Daniel Colascione
2019-03-30 16:16 ` Linus Torvalds
2019-03-30 16:16 ` Linus Torvalds
2019-03-30 16:18 ` Linus Torvalds
2019-03-30 16:18 ` Linus Torvalds
2019-03-31 1:07 ` Joel Fernandes
2019-03-31 1:07 ` Joel Fernandes
2019-03-31 2:34 ` Jann Horn
2019-03-31 2:34 ` Jann Horn
2019-03-31 4:08 ` Joel Fernandes
2019-03-31 4:08 ` Joel Fernandes
2019-03-31 4:46 ` Jann Horn
2019-03-31 4:46 ` Jann Horn
2019-03-31 14:52 ` Linus Torvalds
2019-03-31 14:52 ` Linus Torvalds
2019-03-31 15:05 ` Christian Brauner
2019-03-31 15:05 ` Christian Brauner
2019-03-31 15:21 ` Daniel Colascione [this message]
2019-03-31 15:21 ` Daniel Colascione
2019-03-31 15:33 ` Jonathan Kowalski
2019-03-31 15:33 ` Jonathan Kowalski
2019-03-30 16:19 ` Christian Brauner
2019-03-30 16:19 ` Christian Brauner
2019-03-30 16:24 ` Linus Torvalds
2019-03-30 16:24 ` Linus Torvalds
2019-03-30 16:34 ` Daniel Colascione
2019-03-30 16:34 ` Daniel Colascione
2019-03-30 16:38 ` Christian Brauner
2019-03-30 16:38 ` Christian Brauner
2019-03-30 17:04 ` Linus Torvalds
2019-03-30 17:04 ` Linus Torvalds
2019-03-30 17:12 ` Christian Brauner
2019-03-30 17:12 ` Christian Brauner
2019-03-30 17:24 ` Linus Torvalds
2019-03-30 17:24 ` Linus Torvalds
2019-03-30 17:37 ` Christian Brauner
2019-03-30 17:37 ` Christian Brauner
2019-03-30 17:50 ` Jonathan Kowalski
2019-03-30 17:50 ` Jonathan Kowalski
2019-03-30 17:52 ` Christian Brauner
2019-03-30 17:52 ` Christian Brauner
2019-03-30 17:59 ` Jonathan Kowalski
2019-03-30 17:59 ` Jonathan Kowalski
2019-03-30 18:02 ` Christian Brauner
2019-03-30 18:02 ` Christian Brauner
2019-03-30 18:00 ` Jann Horn
2019-03-30 18:00 ` Jann Horn
2019-03-31 20:09 ` Andy Lutomirski
2019-03-31 20:09 ` Andy Lutomirski
2019-03-31 21:03 ` Linus Torvalds
2019-03-31 21:03 ` Linus Torvalds
2019-03-31 21:10 ` Christian Brauner
2019-03-31 21:10 ` Christian Brauner
2019-03-31 21:17 ` Linus Torvalds
2019-03-31 21:17 ` Linus Torvalds
2019-03-31 22:03 ` Christian Brauner
2019-03-31 22:03 ` Christian Brauner
2019-03-31 22:16 ` Linus Torvalds
2019-03-31 22:16 ` Linus Torvalds
2019-03-31 22:33 ` Christian Brauner
2019-03-31 22:33 ` Christian Brauner
2019-04-01 0:52 ` Jann Horn
2019-04-01 0:52 ` Jann Horn
2019-04-01 8:47 ` Yann Droneaud
2019-04-01 8:47 ` Yann Droneaud
2019-04-01 10:03 ` Jonathan Kowalski
2019-04-01 10:03 ` Jonathan Kowalski
2019-03-31 23:40 ` Linus Torvalds
2019-03-31 23:40 ` Linus Torvalds
2019-04-01 0:09 ` Al Viro
2019-04-01 0:09 ` Al Viro
2019-04-01 0:18 ` Linus Torvalds
2019-04-01 0:18 ` Linus Torvalds
2019-04-01 0:21 ` Christian Brauner
2019-04-01 0:21 ` Christian Brauner
2019-04-01 6:37 ` Al Viro
2019-04-01 6:37 ` Al Viro
2019-04-01 6:41 ` Al Viro
2019-04-01 6:41 ` Al Viro
2019-03-31 22:03 ` Jonathan Kowalski
2019-03-31 22:03 ` Jonathan Kowalski
2019-04-01 2:13 ` Andy Lutomirski
2019-04-01 2:13 ` Andy Lutomirski
2019-04-01 11:40 ` Aleksa Sarai
2019-04-01 11:40 ` Aleksa Sarai
2019-04-01 15:36 ` Linus Torvalds
2019-04-01 15:36 ` Linus Torvalds
2019-04-01 15:47 ` Christian Brauner
2019-04-01 15:47 ` Christian Brauner
2019-04-01 15:55 ` Daniel Colascione
2019-04-01 15:55 ` Daniel Colascione
2019-04-01 16:01 ` Linus Torvalds
2019-04-01 16:01 ` Linus Torvalds
2019-04-01 16:13 ` Daniel Colascione
2019-04-01 16:13 ` Daniel Colascione
2019-04-01 19:42 ` Christian Brauner
2019-04-01 19:42 ` Christian Brauner
2019-04-01 21:30 ` Linus Torvalds
2019-04-01 21:30 ` Linus Torvalds
2019-04-01 21:58 ` Jonathan Kowalski
2019-04-01 21:58 ` Jonathan Kowalski
2019-04-01 22:13 ` Linus Torvalds
2019-04-01 22:13 ` Linus Torvalds
2019-04-01 22:34 ` Daniel Colascione
2019-04-01 22:34 ` Daniel Colascione
2019-04-01 16:07 ` Jonathan Kowalski
2019-04-01 16:07 ` Jonathan Kowalski
2019-04-01 16:15 ` Linus Torvalds
2019-04-01 16:15 ` Linus Torvalds
2019-04-01 16:27 ` Jonathan Kowalski
2019-04-01 16:27 ` Jonathan Kowalski
2019-04-01 16:21 ` Daniel Colascione
2019-04-01 16:21 ` Daniel Colascione
2019-04-01 16:29 ` Linus Torvalds
2019-04-01 16:29 ` Linus Torvalds
2019-04-01 16:45 ` Daniel Colascione
2019-04-01 16:45 ` Daniel Colascione
2019-04-01 17:00 ` David Laight
2019-04-01 17:00 ` David Laight
2019-04-01 17:32 ` Linus Torvalds
2019-04-01 17:32 ` Linus Torvalds
2019-04-02 11:03 ` Florian Weimer
2019-04-02 11:03 ` Florian Weimer
2019-04-01 16:10 ` Andy Lutomirski
2019-04-01 16:10 ` Andy Lutomirski
2019-04-01 12:04 ` Christian Brauner
2019-04-01 12:04 ` Christian Brauner
2019-04-01 13:43 ` Jann Horn
2019-04-01 13:43 ` Jann Horn
2019-03-31 21:19 ` Christian Brauner
2019-03-31 21:19 ` Christian Brauner
2019-03-30 16:37 ` Christian Brauner
2019-03-30 16:37 ` Christian Brauner
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