[PATCH v4 1/6] timer: kasan: record timer stack

[Walter Wu]

When analyze use-after-free or double-free issue, recording the timer
stacks is helpful to preserve usage history which potentially gives
a hint about the affected code.

Record the most recent two timer init calls in KASAN which are printed
on failure in the KASAN report.

For timers it has turned out to be useful to record the stack trace
of the timer init call. Because if the UAF root cause is in timer init,
then user can see KASAN report to get where it is registered and find
out the root cause. It don't need to enable DEBUG_OBJECTS_TIMERS,
but they have a chance to find out the root cause.

Signed-off-by: Walter Wu <walter-zh.wu@xxxxxxxxxxxx>
Suggested-by: Marco Elver <elver@xxxxxxxxxx>
Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Marco Elver <elver@xxxxxxxxxx>
Reviewed-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Stephen Boyd <sboyd@xxxxxxxxxx>
---

v2:
- Thanks for Marco and Thomas suggestion.
- Remove unnecessary code and fix commit log
- reuse kasan_record_aux_stack() and aux_stack
  to record timer and workqueue stack.

---
 kernel/time/timer.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index a16764b0116e..1ed8f8aca7f5 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -796,6 +796,9 @@ static void do_init_timer(struct timer_list *timer,
 	timer->function = func;
 	timer->flags = flags | raw_smp_processor_id();
 	lockdep_init_map(&timer->lockdep_map, name, key, 0);
+
+	/* record the timer stack in order to print it in KASAN report */
+	kasan_record_aux_stack(timer);
 }
 
 /**
-- 
2.18.0