Re: KASAN: use-after-free Read in service_outstanding_interrupt

[Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>]

Hello, Oliver.

I guess that this is caused by not checking WDM_DISCONNECTING/WDM_RESETTING
before usb_submit_urb(), and below diff seems to avoid use-after-free for
the C reproducer syzbot has found.

Since service_outstanding_interrupt() is called from service_interrupt_work()
without holding desc->rlock, it is possible that kill_urbs() is called by
wdm_disconnect() when service_outstanding_interrupt() is preempted between
spin_unlock_irq(&desc->iuspin) and usb_submit_urb(), isn't it?
Therefore, we also need to make sure that kill_urbs(desc) is called after
cancel_work_sync(&desc->service_outs_intr) which waits for
service_interrupt_work() to return completed, don't we?

diff --git a/drivers/usb/class/cdc-wdm.c b/drivers/usb/class/cdc-wdm.c
index 02d0cfd23bb2..508b1c3f8b73 100644
--- a/drivers/usb/class/cdc-wdm.c
+++ b/drivers/usb/class/cdc-wdm.c
@@ -465,13 +465,23 @@ static int service_outstanding_interrupt(struct wdm_device *desc)
 	if (!desc->resp_count || !--desc->resp_count)
 		goto out;
 
+	if (test_bit(WDM_DISCONNECTING, &desc->flags)) {
+		rv = -ENODEV;
+		goto out;
+	}
+	if (test_bit(WDM_RESETTING, &desc->flags)) {
+		rv = -EIO;
+		goto out;
+	}
+
 	set_bit(WDM_RESPONDING, &desc->flags);
 	spin_unlock_irq(&desc->iuspin);
 	rv = usb_submit_urb(desc->response, GFP_KERNEL);
 	spin_lock_irq(&desc->iuspin);
 	if (rv) {
-		dev_err(&desc->intf->dev,
-			"usb_submit_urb failed with result %d\n", rv);
+		if (!test_bit(WDM_DISCONNECTING, &desc->flags))
+			dev_err(&desc->intf->dev,
+				"usb_submit_urb failed with result %d\n", rv);
 
 		/* make sure the next notification trigger a submit */
 		clear_bit(WDM_RESPONDING, &desc->flags);
@@ -1027,9 +1037,9 @@ static void wdm_disconnect(struct usb_interface *intf)
 	wake_up_all(&desc->wait);
 	mutex_lock(&desc->rlock);
 	mutex_lock(&desc->wlock);
-	kill_urbs(desc);
 	cancel_work_sync(&desc->rxwork);
 	cancel_work_sync(&desc->service_outs_intr);
+	kill_urbs(desc);
 	mutex_unlock(&desc->wlock);
 	mutex_unlock(&desc->rlock);