Quoting Bruno Prémont (bonb...@linux-vserver.org):
> On Thu, 11 August 2011 Daniel Lezcano <daniel.lezc...@free.fr> wrote:
> > On 08/11/2011 06:30 PM, Bruno Prémont wrote:
> > > On Wed, 10 August 2011 Daniel Lezcano <daniel.lezc...@free.fr> wrote:
> > >> On 08/10/2011 10:10 PM, Bruno Prémont wrote:
> > >>> Hi Daniel,
> > >>>
> > >>> [I'm adding containers ml as we had a discussion there some time ago
> > >>> for this feature]
> > >> [ ... ]
> > >>
> > >>>> + if (cmd == LINUX_REBOOT_CMD_RESTART2)
> > >>>> + if (strncpy_from_user(&buffer[0], arg, sizeof(buffer) - 1) <
> > >>>> 0)
> > >>>> + return -EFAULT;
> > >>>> +
> > >>>> + /* If we are not in the initial pid namespace, we send a signal
> > >>>> + * to the parent of this init pid namespace, notifying a shutdown
> > >>>> + * occured */
> > >>>> + if (pid_ns != &init_pid_ns)
> > >>>> + pid_namespace_reboot(pid_ns, cmd, buffer);
> > >>> Should there be a return here?
> > >>> Or does pid_namespace_reboot() never return by submitting signal to
> > >>> parent?
> > >> Yes, it does not return a value, like 'do_notify_parent_cldstop'
> > > So execution flow continues reaching the whole "host reboot code"?
> > >
> > > That's not so good as it then prevents using CAP_SYS_BOOT inside PID
> > > namespace
> > > to limit access to rebooting the container from inside as giving a process
> > > inside container CAP_SYS_BOOT would cause host to reboot (and when not
> > > given
> > > process inside container would get -EPERM in all cases).
> > >
> > > Wouldn't the following be better?:
> > > ...
> > > +
> > > + /* We only trust the superuser with rebooting the system. */
> > > + if (!capable(CAP_SYS_BOOT))
> > > + return -EPERM;
> > > +
> > > + /* If we are not in the initial pid namespace, we send a signal
> > > + * to the parent of this init pid namespace, notifying a shutdown
> > > + * occured */
> > > + if (pid_ns != &init_pid_ns) {
> > > + pid_namespace_reboot(pid_ns, cmd, buffer);
> > > + return 0;
> > > + }
> > > +
> > > mutex_lock(&reboot_mutex);
> > > switch (cmd) {
> > > ...
> > >
> > >
> > > If I misunderstood, please correct me.
> >
> > Yep, this is what I did at the beginning but I realized I was closing
> > the door for future applications using the pid namespaces. The pid
> > namespace could be used by another kind of application, not a container,
> > running some administrative tasks so they may want to shutdown the host
> > from a different pid namespace.
> >
> > For this reason, to prevent this execution flow, the container has to
> > drop the CAP_SYS_BOOT in addition of taking care of the SIGCHLD signal
> > with CLDREBOOT.
>
> Ok, though for later source code readers to know adding/extending comment
> would be nice.
> Maybe something like
>
> + /* If we are not in the initial pid namespace, we send a signal
> + * to the parent of this init pid namespace, notifying a shutdown
> + * occured
> + * NOTE: if process has CAP_SYS_BOOT it will additionally have the
> + * same effect as if it was not namespaced */
>
>
> How would all of this integrate with the ongoing work on user namespaces?
> Maybe that one should later be the differentiator for who may or may not
> trigger the host reboot.
Right, then you'll be able to do:
if (ns_capable(current_pid_ns()->user_ns, CAP_SYS_BOOT)) {
// do container reboot stuff
}
if (!capable(CAP_SYS_BOOT)
return;
// do host reboot stuff
The first checks whether the task has privilege against the user ns
which owns his pid_ns.
The second one is a synonym for
if (!ns_capable(&init_user_ns, CAP_SYS_BOOT))
where init_user_ns is the owner of all physical resources.
Right now pid_ns doesn't yet have a user_ns owner (except in my patch over
here:
http://kernel.ubuntu.com/git?p=serge/linux-syslogns.git;a=commit;h=63556e9a39bcd75ec4a88333425800905013c73e
)
and, if it did, well you can't yet do enough in a user namespace to run
a container. But that'll be the ideal. Hopefully soon...
-serge
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