[PATCH v2 1/1] Bluetooth: fix race condition in hidp_session_thread

[Min Li]

There is a potential race condition in hidp_session_thread that may
lead to use-after-free. For instance, the timer is active while
hidp_del_timer is called in hidp_session_thread(). After hidp_session_put,
then 'session' will be freed, causing kernel panic when hidp_idle_timeout
is running.

The solution is to use del_timer_sync instead of del_timer.

Here is the call trace:

? hidp_session_probe+0x780/0x780
call_timer_fn+0x2d/0x1e0
__run_timers.part.0+0x569/0x940
hidp_session_probe+0x780/0x780
call_timer_fn+0x1e0/0x1e0
ktime_get+0x5c/0xf0
lapic_next_deadline+0x2c/0x40
clockevents_program_event+0x205/0x320
run_timer_softirq+0xa9/0x1b0
__do_softirq+0x1b9/0x641
__irq_exit_rcu+0xdc/0x190
irq_exit_rcu+0xe/0x20
sysvec_apic_timer_interrupt+0xa1/0xc0

v2:
  - Fixed code style issues

Signed-off-by: Min Li <lm0963hack@xxxxxxxxx>
---
 net/bluetooth/hidp/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/bluetooth/hidp/core.c b/net/bluetooth/hidp/core.c
index bed1a7b9205c..707f229f896a 100644
--- a/net/bluetooth/hidp/core.c
+++ b/net/bluetooth/hidp/core.c
@@ -433,7 +433,7 @@ static void hidp_set_timer(struct hidp_session *session)
 static void hidp_del_timer(struct hidp_session *session)
 {
 	if (session->idle_to > 0)
-		del_timer(&session->timer);
+		del_timer_sync(&session->timer);
 }
 
 static void hidp_process_report(struct hidp_session *session, int type,
-- 
2.25.1