timerqueue: Use rb_entry_safe() in timerqueue_getnext()

[ Upstream commit 2f117484329b233455ee278f2d9b0a4356835060 ]

When `timerqueue_getnext()` is called on an empty timer queue, it will
use `rb_entry()` on a NULL pointer, which is invalid. Fix that by using
`rb_entry_safe()` which handles NULL pointers.

This has not caused any issues so far because the offset of the `rb_node`
member in `timerqueue_node` is 0, so `rb_entry()` is essentially a no-op.

Fixes: 511885d7061e ("lib/timerqueue: Rely on rbtree semantics for next timer")
Signed-off-by: Barnabás Pőcze <pobrn@protonmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20221114195421.342929-1-pobrn@protonmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/include/linux/timerqueue.h b/include/linux/timerqueue.h
index 9388408..adc80e2 100644 (file)
--- a/include/linux/timerqueue.h
+++ b/include/linux/timerqueue.h
@@ -35,7 +35,7 @@ struct timerqueue_node *timerqueue_getnext(struct timerqueue_head *head)
 {
        struct rb_node *leftmost = rb_first_cached(&head->rb_root);
 
-       return rb_entry(leftmost, struct timerqueue_node, node);
+       return rb_entry_safe(leftmost, struct timerqueue_node, node);
 }
 
 static inline void timerqueue_init(struct timerqueue_node *node)