Re: [PATCH v9 2/4] usb: gadget: uvc: Allocate uvc_requests one at a time

[Dan Scally <dan.scally@ideasonboard.com>]

Hi Avichal

On 27/10/2023 21:19, Avichal Rakesh wrote:
> Currently, the uvc gadget driver allocates all uvc_requests as one array
> and deallocates them all when the video stream stops. This includes
> de-allocating all the usb_requests associated with those uvc_requests.
> This can lead to use-after-free issues if any of those de-allocated
> usb_requests were still owned by the usb controller.
>
> This patch is 1 of 2 patches addressing the use-after-free issue.
> Instead of bulk allocating all uvc_requests as an array, this patch
> allocates uvc_requests one at a time, which should allows for similar
> granularity when deallocating the uvc_requests. This patch has no
> functional changes other than allocating each uvc_request separately,
> and similarly freeing each of them separately.
>
> Link: https://lore.kernel.org/7cd81649-2795-45b6-8c10-b7df1055020d@google.com
> Suggested-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
> Reviewed-by: Daniel Scally <dan.scally@ideasonboard.com>


Sorry - I was unclear in my response to the first patch on v8. I meant my R-b to apply to the first 
patch only rather than to all of them. For this one I understand now the use of the conditional in 
uvc_video_free_request(), so that point is fine. I agree with Greg that the BUG_ON() shouldn't stand 
though.

> Reviewed-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
> Tested-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
> Signed-off-by: Avichal Rakesh <arakesh@google.com>
> ---
> v1 -> v2: Rebased to ToT
> v2 -> v3: Fix email threading goof-up
> v3 -> v4: Address review comments & re-rebase to ToT
> v4 -> v5: Address more review comments. Add Reviewed-by & Tested-by.
> v5 -> v6: No change
> v6 -> v7: No change
> v7 -> v8: No change. Getting back in review queue
> v8 -> v9: Address review comments.
>
>   drivers/usb/gadget/function/uvc.h       |  3 +-
>   drivers/usb/gadget/function/uvc_video.c | 89 ++++++++++++++-----------
>   2 files changed, 52 insertions(+), 40 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/uvc.h b/drivers/usb/gadget/function/uvc.h
> index 989bc6b4e93d..993694da0bbc 100644
> --- a/drivers/usb/gadget/function/uvc.h
> +++ b/drivers/usb/gadget/function/uvc.h
> @@ -81,6 +81,7 @@ struct uvc_request {
>   	struct sg_table sgt;
>   	u8 header[UVCG_REQUEST_HEADER_LEN];
>   	struct uvc_buffer *last_buf;
> +	struct list_head list;
>   };
>
>   struct uvc_video {
> @@ -102,7 +103,7 @@ struct uvc_video {
>
>   	/* Requests */
>   	unsigned int req_size;
> -	struct uvc_request *ureq;
> +	struct list_head ureqs; /* all uvc_requests allocated by uvc_video */
>   	struct list_head req_free;
>   	spinlock_t req_lock;
>
> diff --git a/drivers/usb/gadget/function/uvc_video.c b/drivers/usb/gadget/function/uvc_video.c
> index c334802ac0a4..f8f9209fee50 100644
> --- a/drivers/usb/gadget/function/uvc_video.c
> +++ b/drivers/usb/gadget/function/uvc_video.c
> @@ -227,6 +227,24 @@ uvc_video_encode_isoc(struct usb_request *req, struct uvc_video *video,
>    * Request handling
>    */
>
> +static void
> +uvc_video_free_request(struct uvc_request *ureq, struct usb_ep *ep)
> +{
> +	sg_free_table(&ureq->sgt);
> +	if (ureq->req && ep) {
> +		usb_ep_free_request(ep, ureq->req);
> +		ureq->req = NULL;
> +	}
> +
> +	kfree(ureq->req_buffer);
> +	ureq->req_buffer = NULL;
> +
> +	if (!list_empty(&ureq->list))
> +		list_del_init(&ureq->list);
> +
> +	kfree(ureq);
> +}
> +
>   static int uvcg_video_ep_queue(struct uvc_video *video, struct usb_request *req)
>   {
>   	int ret;
> @@ -293,27 +311,12 @@ uvc_video_complete(struct usb_ep *ep, struct usb_request *req)
>   static int
>   uvc_video_free_requests(struct uvc_video *video)
>   {
> -	unsigned int i;
> -
> -	if (video->ureq) {
> -		for (i = 0; i < video->uvc_num_requests; ++i) {
> -			sg_free_table(&video->ureq[i].sgt);
> +	struct uvc_request *ureq, *temp;
>
> -			if (video->ureq[i].req) {
> -				usb_ep_free_request(video->ep, video->ureq[i].req);
> -				video->ureq[i].req = NULL;
> -			}
> -
> -			if (video->ureq[i].req_buffer) {
> -				kfree(video->ureq[i].req_buffer);
> -				video->ureq[i].req_buffer = NULL;
> -			}
> -		}
> -
> -		kfree(video->ureq);
> -		video->ureq = NULL;
> -	}
> +	list_for_each_entry_safe(ureq, temp, &video->ureqs, list)
> +		uvc_video_free_request(ureq, video->ep);
>
> +	INIT_LIST_HEAD(&video->ureqs);
>   	INIT_LIST_HEAD(&video->req_free);
>   	video->req_size = 0;
>   	return 0;
> @@ -322,39 +325,45 @@ uvc_video_free_requests(struct uvc_video *video)
>   static int
>   uvc_video_alloc_requests(struct uvc_video *video)
>   {
> +	struct uvc_request *ureq;
>   	unsigned int req_size;
>   	unsigned int i;
>   	int ret = -ENOMEM;
>
>   	BUG_ON(video->req_size);
> +	BUG_ON(!list_empty(&video->ureqs));
>
>   	req_size = video->ep->maxpacket
>   		 * max_t(unsigned int, video->ep->maxburst, 1)
>   		 * (video->ep->mult);
>
> -	video->ureq = kcalloc(video->uvc_num_requests, sizeof(struct uvc_request), GFP_KERNEL);
> -	if (video->ureq == NULL)
> -		return -ENOMEM;
> +	for (i = 0; i < video->uvc_num_requests; i++) {
> +		ureq = kzalloc(sizeof(struct uvc_request), GFP_KERNEL);
> +		if (ureq == NULL)
> +			goto error;
> +
> +		INIT_LIST_HEAD(&ureq->list);
> +
> +		list_add_tail(&ureq->list, &video->ureqs);
>
> -	for (i = 0; i < video->uvc_num_requests; ++i) {
> -		video->ureq[i].req_buffer = kmalloc(req_size, GFP_KERNEL);
> -		if (video->ureq[i].req_buffer == NULL)
> +		ureq->req_buffer = kmalloc(req_size, GFP_KERNEL);
> +		if (ureq->req_buffer == NULL)
>   			goto error;
>
> -		video->ureq[i].req = usb_ep_alloc_request(video->ep, GFP_KERNEL);
> -		if (video->ureq[i].req == NULL)
> +		ureq->req = usb_ep_alloc_request(video->ep, GFP_KERNEL);
> +		if (ureq->req == NULL)
>   			goto error;
>
> -		video->ureq[i].req->buf = video->ureq[i].req_buffer;
> -		video->ureq[i].req->length = 0;
> -		video->ureq[i].req->complete = uvc_video_complete;
> -		video->ureq[i].req->context = &video->ureq[i];
> -		video->ureq[i].video = video;
> -		video->ureq[i].last_buf = NULL;
> +		ureq->req->buf = ureq->req_buffer;
> +		ureq->req->length = 0;
> +		ureq->req->complete = uvc_video_complete;
> +		ureq->req->context = ureq;
> +		ureq->video = video;
> +		ureq->last_buf = NULL;
>
> -		list_add_tail(&video->ureq[i].req->list, &video->req_free);
> +		list_add_tail(&ureq->req->list, &video->req_free);
>   		/* req_size/PAGE_SIZE + 1 for overruns and + 1 for header */
> -		sg_alloc_table(&video->ureq[i].sgt,
> +		sg_alloc_table(&ureq->sgt,
>   			       DIV_ROUND_UP(req_size - UVCG_REQUEST_HEADER_LEN,
>   					    PAGE_SIZE) + 2, GFP_KERNEL);
>   	}
> @@ -489,8 +498,8 @@ static void uvcg_video_pump(struct work_struct *work)
>    */
>   int uvcg_video_enable(struct uvc_video *video, int enable)
>   {
> -	unsigned int i;
>   	int ret;
> +	struct uvc_request *ureq;
>
>   	if (video->ep == NULL) {
>   		uvcg_info(&video->uvc->func,
> @@ -502,9 +511,10 @@ int uvcg_video_enable(struct uvc_video *video, int enable)
>   		cancel_work_sync(&video->pump);
>   		uvcg_queue_cancel(&video->queue, 0);
>
> -		for (i = 0; i < video->uvc_num_requests; ++i)
> -			if (video->ureq && video->ureq[i].req)
> -				usb_ep_dequeue(video->ep, video->ureq[i].req);
> +		list_for_each_entry(ureq, &video->ureqs, list) {
> +			if (ureq->req)
> +				usb_ep_dequeue(video->ep, ureq->req);
> +		}
>
>   		uvc_video_free_requests(video);
>   		uvcg_queue_enable(&video->queue, 0);
> @@ -536,6 +546,7 @@ int uvcg_video_enable(struct uvc_video *video, int enable)
>    */
>   int uvcg_video_init(struct uvc_video *video, struct uvc_device *uvc)
>   {
> +	INIT_LIST_HEAD(&video->ureqs);
>   	INIT_LIST_HEAD(&video->req_free);
>   	spin_lock_init(&video->req_lock);
>   	INIT_WORK(&video->pump, uvcg_video_pump);
> --
> 2.42.0.820.g83a721a137-goog