[PATCH] usb: atm: cxacru: fix use-after-free in cxacru_poll_status

[Nguyen Quang Le Kien]

In cxacru_unbind(), cancel_delayed_work_sync() was conditionally skipped
when poll_state was CXPOLL_STOPPED. However, a work item previously
scheduled when poll_state was CXPOLL_POLLING may still be pending in the
workqueue at the time poll_state transitions to CXPOLL_STOPPED. Skipping
cancel_delayed_work_sync() in this case allows the work to fire after
cxacru_data is freed, causing a use-after-free when cxacru_poll_status()
attempts to acquire instance->poll_state_serialize.

Fix this by always calling cancel_delayed_work_sync() regardless of
poll_state, ensuring no pending or in-flight work can access the freed
instance.

Reported-by: syzbot+24eb38c789655fc43663@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=24eb38c789655fc43663
Signed-off-by: Nguyen Quang Le Kien <khiemtranzo532001@xxxxxxxxx>
---
 drivers/usb/atm/cxacru.c | 10 +---------
 1 file changed, 1 insertion(+), 9 deletions(-)

diff --git a/drivers/usb/atm/cxacru.c b/drivers/usb/atm/cxacru.c
index f1900c567..fd644ae52 100644
--- a/drivers/usb/atm/cxacru.c
+++ b/drivers/usb/atm/cxacru.c
@@ -1231,8 +1231,6 @@ static void cxacru_unbind(struct usbatm_data *usbatm_instance,
 		struct usb_interface *intf)
 {
 	struct cxacru_data *instance = usbatm_instance->driver_data;
-	int is_polling = 1;
-
 	usb_dbg(usbatm_instance, "cxacru_unbind entered\n");
 
 	if (!instance) {
@@ -1243,17 +1241,11 @@ static void cxacru_unbind(struct usbatm_data *usbatm_instance,
 	mutex_lock(&instance->poll_state_serialize);
 	BUG_ON(instance->poll_state == CXPOLL_SHUTDOWN);
 
-	/* ensure that status polling continues unless
-	 * it has already stopped */
-	if (instance->poll_state == CXPOLL_STOPPED)
-		is_polling = 0;
-
 	/* stop polling from being stopped or started */
 	instance->poll_state = CXPOLL_SHUTDOWN;
 	mutex_unlock(&instance->poll_state_serialize);
 
-	if (is_polling)
-		cancel_delayed_work_sync(&instance->poll_work);
+	cancel_delayed_work_sync(&instance->poll_work);
 
 	usb_kill_urb(instance->snd_urb);
 	usb_kill_urb(instance->rcv_urb);
-- 
2.34.1