Re: [PATCH v1 2/2] signal: add procfd_signal() syscall

Christian Brauner
2018-11-19T21:13:55Z

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/>
>
>