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 <[email protected]>
> Signed-off-by: Miroslav Benes <[email protected]>
> ---
> 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.
Best Regards,
Petr
PS: I am sorry that I hand waved the proposed solution when
we spoke about it yeasterday. I should have looked into
the code.
