From: Tycho Andersen <tycho@tycho.ws>
To: Daniel Colascione <dancol@google.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
Tim Murray <timmurray@google.com>,
Joel Fernandes <joelaf@google.com>,
Suren Baghdasaryan <surenb@google.com>,
Aleksa Sarai <cyphar@cyphar.com>,
Christian Brauner <christian.brauner@canonical.com>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Kees Cook <keescook@chromium.org>,
Oleg Nesterov <oleg@redhat.com>
Subject: Re: [PATCH v3] Implement /proc/pid/kill
Date: Wed, 31 Oct 2018 14:06:37 -0600 [thread overview]
Message-ID: <20181031200637.GE2180@cisco> (raw)
In-Reply-To: <CAKOZuetdSK8jhD1snja8p4AQTNPrLOugQrVn642RCH8S4QBGFg@mail.gmail.com>
On Wed, Oct 31, 2018 at 07:33:06PM +0000, Daniel Colascione wrote:
> On Wed, Oct 31, 2018 at 6:17 PM, Tycho Andersen <tycho@tycho.ws> wrote:
> > On Wed, Oct 31, 2018 at 06:00:49PM +0000, Daniel Colascione wrote:
> >> On Wed, Oct 31, 2018 at 5:54 PM, Tycho Andersen <tycho@tycho.ws> wrote:
> >> > Why not just use an ioctl() like Jann suggested instead of this big
> >> > security check? Then we avoid the whole setuid writer thing entirely,
> >>
> >> Don't you think a system call would be better than a new ioctl?
> >
> > We already have a kill() system call :)
>
> kill(2) is useless this purpose: it accepts a numeric PID, but we'd
> need it to accept a process file descriptor instead. It's true that
> the existing kill(1) binary might be the vehicle for using a
> hypothetical new system call, but that's a separate matter.
>
> >> With either an ioctl or a new system call, though, the shell would
> >> need a helper program to use the facility, whereas with the existing
> >> approach, the shell can use the new facility without any additional
> >> binaries.
> >
> > ...and a binary to use it!
> >
> > The nice thing about an ioctl is that it avoids this class of attacks
> > entirely.
>
> Let's stop talking about adding an ioctl. Ioctls have problems with
> namespacing of the request argument; it's not safe, in general, to
> issue an ioctl against a file descriptor of an unknown type.
So don't lose track of the fd type. I'm not sure I see this as a big
problem.
> You don't know how that FD will interpret your request code. The two
> good options before us are a write(2) interface and a new system
> call. I think both are defensible. But I don't see a good reason to
> consider adding an ioctl instead of a system call.
https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1729911.html
https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1729921.html
maybe? :)
> All of this is moot if the new comprehensive process interface that
> comes out of LPC ends up being better anyway.
+1, I think a way to do all of this sort of thing would be nice.
> > either. Using this from the shell is still racy, because if I do
> > something like:
> >
> > echo 9 > /proc/$pid/kill
> >
> > There's exactly the same race that there is with kill, that $pid might
> > be something else.
>
> > Of course I could do some magic with bind mounts or
> > my pwd or something to keep it alive, but I can already do that today
> > with kill.
>
> You can't do it today with kill. The idea that keeping a open file
> descriptor to a /proc/pid or a file within it prevents PID reuse is
> widespread, but incorrect.
Good to know :)
Tycho
next prev parent reply other threads:[~2018-10-31 20:06 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-29 22:10 [RFC PATCH] Implement /proc/pid/kill Daniel Colascione
2018-10-30 3:21 ` Joel Fernandes
2018-10-30 8:50 ` Daniel Colascione
2018-10-30 10:39 ` Christian Brauner
2018-10-30 10:40 ` Christian Brauner
2018-10-30 10:48 ` Daniel Colascione
2018-10-30 11:04 ` Christian Brauner
2018-10-30 11:12 ` Daniel Colascione
2018-10-30 11:19 ` Christian Brauner
2018-10-31 5:00 ` Eric W. Biederman
2018-10-30 17:01 ` Joel Fernandes
2018-10-30 5:00 ` Aleksa Sarai
2018-10-30 9:05 ` Daniel Colascione
2018-10-30 20:45 ` Aleksa Sarai
2018-10-30 21:42 ` Joel Fernandes
2018-10-30 22:23 ` Aleksa Sarai
2018-10-30 22:33 ` Joel Fernandes
2018-10-30 22:49 ` Aleksa Sarai
2018-10-31 0:42 ` Joel Fernandes
2018-10-31 1:59 ` Daniel Colascione
2018-10-30 23:10 ` Daniel Colascione
2018-10-30 23:23 ` Christian Brauner
2018-10-30 23:55 ` Daniel Colascione
2018-10-31 2:56 ` Aleksa Sarai
2018-10-31 4:24 ` Joel Fernandes
2018-11-01 20:40 ` Joel Fernandes
2018-11-02 9:46 ` Christian Brauner
2018-11-02 14:34 ` Serge E. Hallyn
2018-10-31 0:57 ` Joel Fernandes
2018-10-31 1:56 ` Daniel Colascione
2018-10-31 4:47 ` Eric W. Biederman
2018-10-31 4:44 ` Eric W. Biederman
2018-10-31 12:44 ` Oleg Nesterov
2018-10-31 13:27 ` Daniel Colascione
2018-10-31 15:10 ` Oleg Nesterov
2018-10-31 15:16 ` Daniel Colascione
2018-10-31 15:49 ` Oleg Nesterov
2018-11-01 11:53 ` David Laight
2018-11-01 15:50 ` Daniel Colascione
2018-10-31 14:37 ` [PATCH v2] " Daniel Colascione
2018-10-31 15:05 ` Joel Fernandes
2018-10-31 17:33 ` Aleksa Sarai
2018-10-31 21:47 ` Joel Fernandes
2018-10-31 15:59 ` [PATCH v3] " Daniel Colascione
2018-10-31 17:54 ` Tycho Andersen
2018-10-31 18:00 ` Daniel Colascione
2018-10-31 18:17 ` Tycho Andersen
2018-10-31 19:33 ` Daniel Colascione
2018-10-31 20:06 ` Tycho Andersen [this message]
2018-11-01 11:33 ` David Laight
2018-11-12 1:19 ` Eric W. Biederman
2018-10-31 16:22 ` [RFC PATCH] " Jann Horn
2018-11-01 4:53 ` Andy Lutomirski
2018-11-12 23:13 ` Pavel Machek
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20181031200637.GE2180@cisco \
--to=tycho@tycho.ws \
--cc=christian.brauner@canonical.com \
--cc=cyphar@cyphar.com \
--cc=dancol@google.com \
--cc=ebiederm@xmission.com \
--cc=joelaf@google.com \
--cc=keescook@chromium.org \
--cc=linux-kernel@vger.kernel.org \
--cc=oleg@redhat.com \
--cc=surenb@google.com \
--cc=timmurray@google.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).