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From: Andy Lutomirski <luto@kernel.org>
To: Daniel Colascione <dancol@google.com>
Cc: Christian Brauner <christian@brauner.io>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	LKML <linux-kernel@vger.kernel.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Jann Horn <jannh@google.com>, Andrew Lutomirski <luto@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Oleg Nesterov <oleg@redhat.com>, Aleksa Sarai <cyphar@cyphar.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Linux FS Devel <linux-fsdevel@vger.kernel.org>,
	Linux API <linux-api@vger.kernel.org>,
	Tim Murray <timmurray@google.com>,
	Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH] proc: allow killing processes via file descriptors
Date: Sun, 18 Nov 2018 07:38:09 -0800	[thread overview]
Message-ID: <CALCETrUd2Y2MmO8Qx8aUvQDOTNiyj35Y7bctPBZe0p2i1EUiLw@mail.gmail.com> (raw)
In-Reply-To: <CAKOZuet3s0WxxPgrtrNkq8YiOWhYAiK6yEio6PKVV9J_H4_TSA@mail.gmail.com>

On Sun, Nov 18, 2018 at 5:59 AM Daniel Colascione <dancol@google.com> wrote:
>
> I had been led to believe that the proposal would be a comprehensive
> process API, not an ioctl basically equivalent to my previous patch.
> If you had a more comprehensive proposal, please just share it on LKML
> instead of limiting the discussion to those able to attend these
> various conferences. If there's some determined opposition to a
> general new process API, this opposition needs a fair and full airing,
> as not everyone can attend these conferences.
>
> On Sun, Nov 18, 2018 at 3:17 AM, Christian Brauner <christian@brauner.io> wrote:
> > With this patch an open() call on /proc/<pid> will give userspace a handle
> > to struct pid of the process associated with /proc/<pid>. This allows to
> > maintain a stable handle on a process.
> > I have been discussing various approaches extensively during technical
> > conferences this year culminating in a long argument with Eric at Linux
> > Plumbers. The general consensus was that having a handle on a process
> > will be something that is very simple and easy to maintain
>
> ioctls are the opposite of "easy to maintain". Their
> file-descriptor-specific behavior makes it difficult to use the things
> safely. If you want to take this approach, please make a new system
> call. An ioctl is just a system call with a very strange spelling and
> unfortunate collision semantics.
>
> > with the
> > option of being extensible via a more advanced api if the need arises.
>
> The need *has* arisen; see my exithand patch.
>
> > I
> > believe that this patch is the most simple, dumb, and therefore
> > maintainable solution.
> >
> > The need for this has arisen in order to reliably kill a process without
> > running into issues of the pid being recycled as has been described in the
> > rejected patch [1].
>
> That patch was not "rejected". It was tabled pending the more
> comprehensive process API proposal that was supposed to have emerged.
> This patch is just another variant of the sort of approach we
> discussed on that patch's thread here. As I mentioned on that thread,
> the right approach option is a new system call, not an ioctl.
>
>  To fulfill the need described in that patchset a new
> > ioctl() PROC_FD_SIGNAL is added. It can be used to send signals to a
> > process via a file descriptor:
> >
> > int fd = open("/proc/1234", O_DIRECTORY | O_CLOEXEC);
> > ioctl(fd, PROC_FD_SIGNAL, SIGKILL);
> > close(fd);
> >
> > Note, the stable handle will allow us to carefully extend this feature in
> > the future.
>
> We still need the ability to synchronously wait on a process's death,
> as in my patch set. I will be refreshing that patch set.

I fully agree that a more comprehensive, less expensive API for
managing processes would be nice.  But I also think that this patch
(using the directory fd and ioctl) is better from a security
perspective than using a new file in /proc.

I have an old patch to make proc directory fds pollable:

https://lore.kernel.org/patchwork/patch/345098/

That patch plus the one in this thread might make a nice addition to
the kernel even if we expect something much better to come along
later.

This patch that uses ioctl

  reply	other threads:[~2018-11-18 15:38 UTC|newest]

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-18 11:17 Christian Brauner
2018-11-18 13:59 ` Daniel Colascione
2018-11-18 15:38   ` Andy Lutomirski [this message]
2018-11-18 15:53     ` Daniel Colascione
2018-11-18 16:17       ` Andy Lutomirski
2018-11-18 16:29         ` Daniel Colascione
2018-11-18 17:13           ` Andy Lutomirski
2018-11-18 17:17             ` Daniel Colascione
2018-11-18 17:43               ` Eric W. Biederman
2018-11-18 17:45                 ` Andy Lutomirski
2018-11-18 17:56                 ` Daniel Colascione
2018-11-18 16:33         ` Randy Dunlap
2018-11-18 16:48           ` Daniel Colascione
2018-11-18 17:09             ` Andy Lutomirski
2018-11-18 17:24               ` Daniel Colascione
2018-11-18 17:42                 ` Andy Lutomirski
2018-11-18 17:51                   ` Daniel Colascione
2018-11-18 18:28                     ` Andy Lutomirski
2018-11-18 18:43                       ` Daniel Colascione
2018-11-18 19:05                         ` Aleksa Sarai
2018-11-18 19:44                           ` Daniel Colascione
2018-11-18 20:15                             ` Christian Brauner
2018-11-18 20:21                               ` Daniel Colascione
2018-11-18 20:28                             ` Andy Lutomirski
2018-11-18 20:32                               ` Daniel Colascione
2018-11-19  1:43                                 ` Andy Lutomirski
2018-11-18 20:43                               ` Christian Brauner
2018-11-18 20:54                                 ` Daniel Colascione
2018-11-18 21:23                                   ` Christian Brauner
2018-11-18 21:30                                     ` Christian Brauner
2018-11-19  0:31                                       ` Daniel Colascione
2018-11-19  0:40                                         ` Christian Brauner
2018-11-19  0:09                             ` Aleksa Sarai
2018-11-19  0:53                               ` Daniel Colascione
2018-11-19  1:16                                 ` Daniel Colascione
2018-11-19 16:13                       ` Dmitry Safonov
2018-11-19 16:26                         ` [PATCH] proc: allow killing processes via file descriptors (Larger pids) Eric W. Biederman
2018-11-19 16:27                         ` [PATCH] proc: allow killing processes via file descriptors Daniel Colascione
2018-11-19 20:21                           ` Aleksa Sarai
2018-11-19  2:47                   ` Al Viro
2018-11-19  3:01                     ` Andy Lutomirski
2018-11-18 17:41     ` Christian Brauner
2018-11-18 17:44       ` Andy Lutomirski
2018-11-18 18:07       ` Daniel Colascione
2018-11-18 18:15         ` Andy Lutomirski
2018-11-18 18:31           ` Daniel Colascione
2018-11-18 19:24         ` Christian Brauner
2018-11-19  0:08         ` Aleksa Sarai
2018-11-19  1:14           ` Daniel Colascione
2018-11-18 16:03 ` Daniel Colascione
2018-11-19 10:56 ` kbuild test robot
2018-11-19 14:15 ` David Laight
2018-11-19 15:49 ` Dave Martin

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