On Wed, 20 Dec 2017, Petr Mladek wrote:
> On Wed 2017-12-20 10:28:07, Miroslav Benes wrote:
> > klp_send_signals() and klp_force_transition() do not acquire klp_mutex,
> > because it seemed to be superfluous. A potential race in
> > klp_send_signals() was harmless and there was nothing in
> > klp_force_transition() which needed to be synchronized. That changed
> > with the addition of klp_forced variable during the review process.
> >
> > There is a small window now, when klp_complete_transition() does not see
> > klp_forced set to true while all tasks have been already transitioned to
> > the target state. module_put() is called and the module can be removed.
> >
> > Acquire klp_mutex to prevent it. Do the same in klp_send_signals() just
> > to be sure. There is no real downside to that.
> >
> > Reported-by: Jason Baron <jbaron@xxxxxxxxxx>
> > Signed-off-by: Miroslav Benes <mbenes@xxxxxxx>
> > ---
> > kernel/livepatch/transition.c | 8 ++++++++
> > 1 file changed, 8 insertions(+)
> >
> > diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
> > index be5bfa533ee8..3f932ff607cd 100644
> > --- a/kernel/livepatch/transition.c
> > +++ b/kernel/livepatch/transition.c
> > @@ -625,6 +625,8 @@ void klp_send_signals(void)
> >
> > pr_notice("signaling remaining tasks\n");
> >
> > + mutex_lock(&klp_mutex);
> > +
> > read_lock(&tasklist_lock);
> > for_each_process_thread(g, task) {
> > if (!klp_patch_pending(task))
> > @@ -653,6 +655,8 @@ void klp_send_signals(void)
> > }
> > }
> > read_unlock(&tasklist_lock);
> > +
> > + mutex_unlock(&klp_mutex);
>
> It would be cleaner if the lock guarded also the check:
>
> if (patch != klp_transition_patch)
> return -EINVAL;
>
> in signal_store(). Then we could remove also the comment
> above this check.
>
> Same is true also for the force part stuff.
And I even left obsolete comments in sysfs callbacks. Sigh. v2 is
inevitable...
Miroslav
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