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;
Date:   Mon, 19 Nov 2018 22:13:43 +0100
From:   Christian Brauner <christian@brauner.io>
To:     Aleksa Sarai <cyphar@cyphar.com>
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
Message-ID: <20181119211335.tmoycnu4r2ob6cda@brauner.io>
References: <20181119103241.5229-1-christian@brauner.io>
 <20181119103241.5229-3-christian@brauner.io>
 <20181119202857.k5zw742xjfrw677j@yavin>
 <20181119205518.btew3vxwgva4w3zh@brauner.io>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <20181119205518.btew3vxwgva4w3zh@brauner.io>
User-Agent: NeoMutt/20180716
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Mon, Nov 19, 2018 at 09:55:18PM +0100, Christian Brauner 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

To be more precise, we need to detect if fd refers to an ancestor pidns
and if so return EINVAL.

> 
> > allow process creation this would allow a container to create a process
> > outside its pidns.
> > 
> > -- 
> > Aleksa Sarai
> > Senior Software Engineer (Containers)
> > SUSE Linux GmbH
> > <https://www.cyphar.com/>
> 
>