[PATCH] genirq: fix reference leaks on irq affinity notifiers

[Edward Cree <ecree@solarflare.com>]

The handling of notify->work did not properly maintain notify->kref in two
 cases:
1) where the work was already scheduled, another irq_set_affinity_locked()
   would get the ref and (no-op-ly) schedule the work.  Thus when
   irq_affinity_notify() ran, it would drop the original ref but not the
   additional one.
2) when cancelling the (old) work in irq_set_affinity_notifier(), if there
   was outstanding work a ref had been got for it but was never put.
Fix both by checking the return values of the work handling functions
 (schedule_work() for (1) and cancel_work_sync() for (2)) and put the
 extra ref if the return value indicates preexisting work.

Fixes: cd7eab44e994 ("genirq: Add IRQ affinity notifiers")
Fixes: 59c39840f5ab ("genirq: Prevent use-after-free and work list corruption")
Signed-off-by: Edward Cree <ecree@solarflare.com>
---
 kernel/irq/manage.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 7eee98c38f25..b3aa1db895e6 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -323,7 +323,10 @@ int irq_set_affinity_locked(struct irq_data *data, const struct cpumask *mask,
 
 	if (desc->affinity_notify) {
 		kref_get(&desc->affinity_notify->kref);
-		schedule_work(&desc->affinity_notify->work);
+		if (!schedule_work(&desc->affinity_notify->work))
+			/* Work was already scheduled, drop our extra ref */
+			kref_put(&desc->affinity_notify->kref,
+				 desc->affinity_notify->release);
 	}
 	irqd_set(data, IRQD_AFFINITY_SET);
 
@@ -423,7 +426,9 @@ irq_set_affinity_notifier(unsigned int irq, struct irq_affinity_notify *notify)
 	raw_spin_unlock_irqrestore(&desc->lock, flags);
 
 	if (old_notify) {
-		cancel_work_sync(&old_notify->work);
+		if (cancel_work_sync(&old_notify->work))
+			/* Pending work had a ref, put that one too */
+			kref_put(&old_notify->kref, old_notify->release);
 		kref_put(&old_notify->kref, old_notify->release);
 	}