[PATCH v3] hrtimer: check hrtimer with a NULL function

[Phil Chang]

To prevent improper usage of hrtimers and avoid potential kernel crashes,
this commit introduces a validation check for hrtimers with a valid function callback,
discard the hrtimers that have a NULL callback.

The `run_hrtimer` executes callbacks for every hrtimer,
and these callbacks must not be NULL. A NULL callback can lead to a kernel crash.
This update ensures that all hrtimers have properly initialized callbacks
before execution.

Signed-off-by: Phil Chang <phil.chang@xxxxxxxxxxxx>
---
 kernel/time/hrtimer.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 492c14aac642..b8ee320208d4 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1285,6 +1285,8 @@ void hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,
 	struct hrtimer_clock_base *base;
 	unsigned long flags;
 
+	if (WARN_ON_ONCE(!timer->function))
+		return;
 	/*
 	 * Check whether the HRTIMER_MODE_SOFT bit and hrtimer.is_soft
 	 * match on CONFIG_PREEMPT_RT = n. With PREEMPT_RT check the hard
-- 
2.18.0