usb: gadget: u_audio: fix race condition on endpoint stop

If the endpoint completion callback is call right after the ep_enabled flag
is cleared and before usb_ep_dequeue() is call, we could do a double free
on the request and the associated buffer.

Fix this by clearing ep_enabled after all the endpoint requests have been
dequeued.

Fixes: 7de8681 ("usb: gadget: u_audio: Free requests only after callback")
Cc: stable <stable@vger.kernel.org>
Reported-by: Thinh Nguyen <Thinh.Nguyen@synopsys.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://lore.kernel.org/r/20210827092927.366482-1-jbrunet@baylibre.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/function/u_audio.c

@@ -394,8 +394,6 @@ static inline void free_ep(struct uac_rtd_params *prm, struct usb_ep *ep)
 	if (!prm->ep_enabled)
 		return;
 
-	prm->ep_enabled = false;
-
 	audio_dev = uac->audio_dev;
 	params = &audio_dev->params;
 
@@ -413,6 +411,8 @@ static inline void free_ep(struct uac_rtd_params *prm, struct usb_ep *ep)
 		}
 	}
 
+	prm->ep_enabled = false;
+
 	if (usb_ep_disable(ep))
 		dev_err(uac->card->dev, "%s:%d Error!\n", __func__, __LINE__);
 }
@@ -424,8 +424,6 @@ static inline void free_ep_fback(struct uac_rtd_params *prm, struct usb_ep *ep)
 	if (!prm->fb_ep_enabled)
 		return;
 
-	prm->fb_ep_enabled = false;
-
 	if (prm->req_fback) {
 		if (usb_ep_dequeue(ep, prm->req_fback)) {
 			kfree(prm->req_fback->buf);
@@ -434,6 +432,8 @@ static inline void free_ep_fback(struct uac_rtd_params *prm, struct usb_ep *ep)
 		prm->req_fback = NULL;
 	}
 
+	prm->fb_ep_enabled = false;
+
 	if (usb_ep_disable(ep))
 		dev_err(uac->card->dev, "%s:%d Error!\n", __func__, __LINE__);
 }