2023-04-21 08:42:53

by Duoming Zhou

Subject: [PATCH] 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 <[email protected]>
---
drivers/input/touchscreen/cyttsp4_core.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/input/touchscreen/cyttsp4_core.c b/drivers/input/touchscreen/cyttsp4_core.c
index 0cd6f626ade..7cb26929dc7 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)
--
2.17.1

2023-05-02 00:42:03

by Dmitry Torokhov

Subject: Re: [PATCH] Input: cyttsp4_core - change del_timer_sync() to timer_shutdown_sync()

On Fri, Apr 21, 2023 at 04:29:19PM +0800, Duoming Zhou wrote:
> 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 <[email protected]>

Applied, thank you.

--
Dmitry