On Thu 29 Oct 2020 at 18:59, Jack Pham <jackp@xxxxxxxxxxxxxx> wrote:
> As per the kernel doc for usb_ep_dequeue(), it states that "this
> routine is asynchronous, that is, it may return before the completion
> routine runs". And indeed since v5.0 the dwc3 gadget driver updated
> its behavior to place dequeued requests on to a cancelled list to be
> given back later after the endpoint is stopped.
>
> The free_ep() was incorrectly assuming that a request was ready to
> be freed after calling dequeue which results in a use-after-free
> in dwc3 when it traverses its cancelled list. Fix this by moving
> the usb_ep_free_request() call to the callback itself in case the
> ep is disabled.
>
> Fixes: eb9fecb9e69b0 ("usb: gadget: f_uac2: split out audio core")
> Reported-and-tested-by: Ferry Toth <fntoth@xxxxxxxxx>
> Reviewed-and-tested-by: Peter Chen <peter.chen@xxxxxxx>
Tested-by: Jerome Brunet <jbrunet@xxxxxxxxxxxx>
> Signed-off-by: Jack Pham <jackp@xxxxxxxxxxxxxx>
> ---
> v3: Fixed incorrect 'req' parameter and added Peter's tag
>
> v2: call free_request() in case of ep_dequeue() failure
>
> drivers/usb/gadget/function/u_audio.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/u_audio.c b/drivers/usb/gadget/function/u_audio.c
> index e6d32c536781..6e69ccf02c95 100644
> --- a/drivers/usb/gadget/function/u_audio.c
> +++ b/drivers/usb/gadget/function/u_audio.c
> @@ -89,7 +89,12 @@ static void u_audio_iso_complete(struct usb_ep *ep, struct usb_request *req)
> struct snd_uac_chip *uac = prm->uac;
>
> /* i/f shutting down */
> - if (!prm->ep_enabled || req->status == -ESHUTDOWN)
> + if (!prm->ep_enabled) {
> + usb_ep_free_request(ep, req);
> + return;
> + }
> +
> + if (req->status == -ESHUTDOWN)
> return;
>
> /*
> @@ -336,8 +341,9 @@ static inline void free_ep(struct uac_rtd_params *prm, struct usb_ep *ep)
>
> for (i = 0; i < params->req_number; i++) {
> if (prm->ureq[i].req) {
> - usb_ep_dequeue(ep, prm->ureq[i].req);
> - usb_ep_free_request(ep, prm->ureq[i].req);
> + if (usb_ep_dequeue(ep, prm->ureq[i].req))
> + usb_ep_free_request(ep, prm->ureq[i].req);
> + /* else will be freed in u_audio_iso_complete() */
> prm->ureq[i].req = NULL;
> }
> }
