linux-kernel - [PATCH v2] timerqueue: use rb_entry_safe() in timerqueue

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Date:   Mon, 14 Nov 2022 19:54:23 +0000
From:   Barnabás Pőcze <pobrn@...tonmail.com>
To:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        John Stultz <jstultz@...gle.com>
Subject: [PATCH v2] timerqueue: use rb_entry_safe() in timerqueue_getnext()

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@...tonmail.com>
---
changes in v2:
 - reword commit message

---
 include/linux/timerqueue.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/timerqueue.h b/include/linux/timerqueue.h
index 93884086f392..adc80e29168e 100644
--- 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)
--
2.38.1