From: Duoming Zhou duoming@zju.edu.cn

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.

Cc: stable@vger.kernel.org Fixes: CVE-2023-4134 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 Signed-off-by: Denis Efremov (Oracle) efremov@linux.com ---

I've only added Cc: stable and Fixes tag.

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 dccbcb942fe5..f999265896f4 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)