Re: [PATCH][BUGFIX] cgroups: fix pid namespace bug

Serge E. Hallyn
2009-07-02T16:37:39Z

Quoting Paul Menage (menage@google.com):
> On Wed, Jul 1, 2009 at 6:24 PM, Li Zefan<lizf@cn.fujitsu.com> wrote:
> > +       cp = kzalloc(sizeof(*cp), GFP_KERNEL);
> > +       if (!cp) {
> > +               up_write(&cgrp->pids_mutex);
> > +               kfree(pidarray);
> > +               return -ENOMEM;
> > +       }
> > +       cp->cgrp = cgrp;
> > +       cp->pid_ns = pid_ns;
>
> You're storing an uncounted reference to the pid ns here - there's no
> guarantee that the pid_ns will outlive the open file.

Yeah I was thinking about that, but

1. the only way it won't outlive the open file is if the
task opens the file, hands the open fd over a
unix socket, then exits as the last task of its
pidns
2. We don't dereference the pid_ns, so there is no actual
safety issue. So it would become a problem only
if a new pidns gets created at that same address
*and* a task in the new pidns opens the same
tasks file.

Still, it wouldn't hurt to do get_pid_ns/put_pid_ns at the open
and release :)

-serge