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From: Aleksa Sarai <cyphar@cyphar.com>
To: Christian Brauner <christian@brauner.io>
Cc: ebiederm@xmission.com, linux-kernel@vger.kernel.org,
	serge@hallyn.com, jannh@google.com, luto@kernel.org,
	akpm@linux-foundation.org, oleg@redhat.com,
	viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org,
	linux-api@vger.kernel.org, dancol@google.com,
	timmurray@google.com, linux-man@vger.kernel.org,
	Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH v1 2/2] signal: add procfd_signal() syscall
Date: Tue, 20 Nov 2018 08:25:19 +1100
Message-ID: <20181119212519.yqh7qldznqwct3dv@yavin> (raw)
In-Reply-To: <20181119212126.u2nkijmula6wcfqi@brauner.io>


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On 2018-11-19, Christian Brauner <christian@brauner.io> wrote:
> On Tue, Nov 20, 2018 at 08:18:10AM +1100, Aleksa Sarai wrote:
> > On 2018-11-19, Christian Brauner <christian@brauner.io> wrote:
> > > On Tue, Nov 20, 2018 at 07:28:57AM +1100, Aleksa Sarai wrote:
> > > > On 2018-11-19, Christian Brauner <christian@brauner.io> wrote:
> > > > > +	if (info) {
> > > > > +		ret = __copy_siginfo_from_user(sig, &kinfo, info);
> > > > > +		if (unlikely(ret))
> > > > > +			goto err;
> > > > > +		/*
> > > > > +		 * Not even root can pretend to send signals from the kernel.
> > > > > +		 * Nor can they impersonate a kill()/tgkill(), which adds
> > > > > +		 * source info.
> > > > > +		 */
> > > > > +		ret = -EPERM;
> > > > > +		if ((kinfo.si_code >= 0 || kinfo.si_code == SI_TKILL) &&
> > > > > +		    (task_pid(current) != pid))
> > > > > +			goto err;
> > > > > +	} else {
> > > > > +		prepare_kill_siginfo(sig, &kinfo);
> > > > > +	}
> > > > 
> > > > I wonder whether we should also have a pidns restriction here, since
> > > > currently it isn't possible for a container process using a pidns to
> > > > signal processes outside its pidns. AFAICS, this isn't done through an
> > > > explicit check -- it's a side-effect of processes in a pidns not being
> > > > able to address non-descendant-pidns processes.
> > > > 
> > > > But maybe it's reasonable to allow sending a procfd to a different pidns
> > > > and the same operations working on it? If we extend the procfd API to
> > > 
> > > No, I don't think so. I really don't want any fancy semantics in here.
> > > Fancy doesn't get merged and fancy is hard to maintain. So we should do
> > > something like:
> > > 
> > > if (proc_pid_ns() != current_pid_ns)
> > > 	return EINVAL
> > 
> > This isn't quite sufficient. The key thing is that you have to be in an
> > *ancestor* (or same) pidns, not the *same* pidns. Ideally you can re-use
> > the check already in pidns_get_parent, and expose it. It would be
> > something as trivial as:
> > 
> > bool pidns_is_descendant(struct pid_namespace *ns,
> >                          struct pid_namespace *ancestor)
> > {
> >     for (;;) {
> >         if (!ns)
> >             return false;
> >         if (ns == ancestor)
> >             break;
> >         ns = ns->parent;
> >     }
> >     return true;
> > }
> 
> That can be done without a loop by comparing the level counter for the
> two pid namespaces.

If so, we can refactor how pidns_get_parent() and family work. :P

But yes, I agree with doing the above check.

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

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  reply index

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-19 10:32 [PATCH v1 0/2] proc: allow signaling processes via file descriptors Christian Brauner
2018-11-19 10:32 ` [PATCH v1 1/2] proc: get process file descriptor from /proc/<pid> Christian Brauner
2018-11-19 15:32   ` Andy Lutomirski
2018-11-19 18:20     ` Christian Brauner
2018-11-19 10:32 ` [PATCH v1 2/2] signal: add procfd_signal() syscall Christian Brauner
2018-11-19 15:45   ` Andy Lutomirski
2018-11-19 15:57     ` Daniel Colascione
2018-11-19 18:39     ` Christian Brauner
2018-11-19 15:59   ` Daniel Colascione
2018-11-19 18:29     ` Christian Brauner
2018-11-19 19:02       ` Eric W. Biederman
2018-11-19 19:31         ` Christian Brauner
2018-11-19 19:39           ` Daniel Colascione
2018-11-19 17:10   ` Eugene Syromiatnikov
2018-11-19 18:23     ` Christian Brauner
2018-11-19 17:14   ` Eugene Syromiatnikov
2018-11-19 20:28   ` Aleksa Sarai
2018-11-19 20:55     ` Christian Brauner
2018-11-19 21:13       ` Christian Brauner
2018-11-19 21:18       ` Aleksa Sarai
2018-11-19 21:20         ` Christian Brauner
2018-11-19 21:21         ` Christian Brauner
2018-11-19 21:25           ` Aleksa Sarai [this message]
2018-11-19 21:26           ` Daniel Colascione
2018-11-19 21:36             ` Aleksa Sarai
2018-11-19 21:37             ` Christian Brauner
2018-11-19 21:41               ` Daniel Colascione
2018-11-20  4:59                 ` Eric W. Biederman
2018-11-20 10:31                   ` Christian Brauner
2018-11-21 21:39                     ` Serge E. Hallyn
2018-11-19 21:23         ` Aleksa Sarai
2018-11-22  7:41           ` Serge E. Hallyn
2018-11-19 22:39   ` Tycho Andersen
2018-11-19 22:49     ` Daniel Colascione
2018-11-19 23:07       ` Tycho Andersen
2018-11-20  0:27         ` Andy Lutomirski
2018-11-20  0:32           ` Christian Brauner
2018-11-20  0:34             ` Andy Lutomirski
2018-11-20  0:49           ` Daniel Colascione
2018-11-22  7:48     ` Serge E. Hallyn
2018-11-19 23:35   ` kbuild test robot
2018-11-19 23:37   ` kbuild test robot
2018-11-19 23:45     ` Christian Brauner
2018-11-28 21:45   ` Joey Pabalinas
2018-11-28 22:05     ` Christian Brauner
2018-11-28 23:02       ` Joey Pabalinas
2018-11-19 10:32 ` [PATCH] procfd_signal.2: document procfd_signal syscall Christian Brauner
2018-11-20 13:29   ` Michael Kerrisk (man-pages)
2018-11-28 20:59   ` Florian Weimer
2018-11-28 21:12     ` Christian Brauner

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