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

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

[Denis Efremov (Oracle)]

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)
-- 
2.42.0

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

[Greg KH]

On Fri, Sep 08, 2023 at 05:41:35AM +0400, Denis Efremov (Oracle) wrote:
> 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

"CVE" is not a valid Fixes tag :(

> 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.

What is the commit id in Linus's tree for this?

thanks,

greg k-h

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

[Denis Efremov (Oracle)]

On 9/8/23 10:15, Greg KH wrote:
> On Fri, Sep 08, 2023 at 05:41:35AM +0400, Denis Efremov (Oracle) wrote:
>> 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
> 
> "CVE" is not a valid Fixes tag :(
> 
>> 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.
> 

Please, don't take this patch. It breaks the build. Sorry, I forgot to check it this time.
I'll resend a correct backport with the upstream commit info.

Best Regards,
Denis