[PATCH v3] usb: gadget: audio: Free requests only after callback

[PATCH v3] usb: gadget: audio: Free requests only after callback

[Jack Pham]

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@gmail.com>
Reviewed-and-tested-by: Peter Chen <peter.chen@nxp.com>
Signed-off-by: Jack Pham <jackp@codeaurora.org>
---
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;
 		}
 	}
-- 
2.24.0

Re: [PATCH v3] usb: gadget: audio: Free requests only after callback

[Ferry Toth]

Hi

Op 29-10-2020 om 18:59 schreef Jack Pham:
> 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@gmail.com>
> Reviewed-and-tested-by: Peter Chen<peter.chen@nxp.com>
> Signed-off-by: Jack Pham<jackp@codeaurora.org>
> ---
> 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;
>   		}
>   	}

I retested this version on edison. It resolves also another issue where 
dwc3 (in gadget mode) was periodically resetting.

Thanks!

Re: [PATCH v3] usb: gadget: audio: Free requests only after callback

[Jerome Brunet]

On Thu 29 Oct 2020 at 18:59, Jack Pham <jackp@codeaurora.org> 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@gmail.com>
> Reviewed-and-tested-by: Peter Chen <peter.chen@nxp.com>

Tested-by: Jerome Brunet <jbrunet@baylibre.com>

> Signed-off-by: Jack Pham <jackp@codeaurora.org>
> ---
> 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;
>  		}
>  	}