From: Duoming Zhou <duoming@zju.edu.cn>
Date: Tue, 2 May 2023 00:37:02 +0000 (-0700)
Subject: Input: cyttsp4_core - change del_timer_sync() to timer_shutdown_sync()
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=dbe836576f12743a7d2d170ad4ad4fd324c4d47a;p=linux.git

Input: cyttsp4_core - change del_timer_sync() to timer_shutdown_sync()

The watchdog_timer can schedule tx_timeout_task and watchdog_work
can also arm watchdog_timer. The process is shown below:

----------- timer schedules work ------------
cyttsp4_watchdog_timer() //timer handler
  schedule_work(&cd->watchdog_work)

----------- work arms timer ------------
cyttsp4_watchdog_work() //workqueue callback function
  cyttsp4_start_wd_timer()
    mod_timer(&cd->watchdog_timer, ...)

Although del_timer_sync() and cancel_work_sync() are called in
cyttsp4_remove(), the timer and workqueue could still be rearmed.
As a result, the possible use after free bugs could happen. The
process is shown below:

  (cleanup routine)           |  (timer and workqueue routine)
cyttsp4_remove()              | cyttsp4_watchdog_timer() //timer
  cyttsp4_stop_wd_timer()     |   schedule_work()
    del_timer_sync()          |
                              | cyttsp4_watchdog_work() //worker
                              |   cyttsp4_start_wd_timer()
                              |     mod_timer()
    cancel_work_sync()        |
                              | cyttsp4_watchdog_timer() //timer
                              |   schedule_work()
    del_timer_sync()          |
  kfree(cd) //FREE            |
                              | cyttsp4_watchdog_work() // reschedule!
                              |   cd-> //USE

This patch changes del_timer_sync() to timer_shutdown_sync(),
which could prevent rearming of the timer from the workqueue.

Fixes: 17fb1563d69b ("Input: cyttsp4 - add core driver for Cypress TMA4XX touchscreen devices")
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Link: https://lore.kernel.org/r/20230421082919.8471-1-duoming@zju.edu.cn
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
---

diff --git a/drivers/input/touchscreen/cyttsp4_core.c b/drivers/input/touchscreen/cyttsp4_core.c
index 0cd6f626adec5..7cb26929dc732 100644
--- a/drivers/input/touchscreen/cyttsp4_core.c
+++ b/drivers/input/touchscreen/cyttsp4_core.c
@@ -1263,9 +1263,8 @@ static void cyttsp4_stop_wd_timer(struct cyttsp4 *cd)
 	 * Ensure we wait until the watchdog timer
 	 * running on a different CPU finishes
 	 */
-	del_timer_sync(&cd->watchdog_timer);
+	timer_shutdown_sync(&cd->watchdog_timer);
 	cancel_work_sync(&cd->watchdog_work);
-	del_timer_sync(&cd->watchdog_timer);
 }
 
 static void cyttsp4_watchdog_timer(struct timer_list *t)