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Date:   Wed, 18 Oct 2023 15:03:00 +0200
From:   Michael Grzeschik <mgr@pengutronix.de>
To:     Avichal Rakesh <arakesh@google.com>
Cc:     dan.scally@ideasonboard.com, laurent.pinchart@ideasonboard.com,
        etalvala@google.com, gregkh@linuxfoundation.org,
        jchowdhary@google.com, linux-kernel@vger.kernel.org,
        linux-usb@vger.kernel.org
Subject: Re: [PATCH v4 2/3] usb: gadget: uvc: Allocate uvc_requests one at a
 time
Message-ID: <ZS/XhFNvnevol9MP@pengutronix.de>
References: <20230930184821.310143-1-arakesh@google.com>
 <20231012002451.254737-1-arakesh@google.com>
 <20231012002451.254737-2-arakesh@google.com>
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A short second review.

On Wed, Oct 11, 2023 at 05:24:50PM -0700, 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: 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
>
> drivers/usb/gadget/function/uvc.h       |  3 +-
> drivers/usb/gadget/function/uvc_video.c | 87 ++++++++++++++-----------
> 2 files changed, 50 insertions(+), 40 deletions(-)
>
>diff --git a/drivers/usb/gadget/function/uvc.h b/drivers/usb/gadget/functi=
on/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..b62b3de79153 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 =3D NULL;
>+	}
>+
>+	kfree(ureq->req_buffer);
>+	ureq->req_buffer =3D 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_reques=
t *req)
> {
> 	int ret;
>@@ -293,27 +311,12 @@ uvc_video_complete(struct usb_ep *ep, struct usb_req=
uest *req)
> static int
> uvc_video_free_requests(struct uvc_video *video)
> {
>-	unsigned int i;
>+	struct uvc_request *ureq, *temp;
>
>-	if (video->ureq) {
>-		for (i =3D 0; i < video->uvc_num_requests; ++i) {
>-			sg_free_table(&video->ureq[i].sgt);
>-
>-			if (video->ureq[i].req) {
>-				usb_ep_free_request(video->ep, video->ureq[i].req);
>-				video->ureq[i].req =3D NULL;
>-			}
>-
>-			if (video->ureq[i].req_buffer) {
>-				kfree(video->ureq[i].req_buffer);
>-				video->ureq[i].req_buffer =3D NULL;
>-			}
>-		}
>-
>-		kfree(video->ureq);
>-		video->ureq =3D 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 =3D 0;
> 	return 0;
>@@ -322,6 +325,7 @@ 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 =3D -ENOMEM;
>@@ -332,29 +336,32 @@ uvc_video_alloc_requests(struct uvc_video *video)
> 		 * max_t(unsigned int, video->ep->maxburst, 1)
> 		 * (video->ep->mult);
>
>-	video->ureq =3D kcalloc(video->uvc_num_requests, sizeof(struct uvc_reque=
st), GFP_KERNEL);
>-	if (video->ureq =3D=3D NULL)
>-		return -ENOMEM;
>+	INIT_LIST_HEAD(&video->ureqs);
>+	for (i =3D 0; i < video->uvc_num_requests; i++) {
>+		ureq =3D kzalloc(sizeof(struct uvc_request), GFP_KERNEL);
>+		if (ureq =3D=3D NULL)
>+			goto error;
Please add an empty line here.
>+		INIT_LIST_HEAD(&ureq->list);

Please add an empty line here.

>+		list_add_tail(&ureq->list, &video->ureqs);
>
>-	for (i =3D 0; i < video->uvc_num_requests; ++i) {
>-		video->ureq[i].req_buffer =3D kmalloc(req_size, GFP_KERNEL);
>-		if (video->ureq[i].req_buffer =3D=3D NULL)
>+		ureq->req_buffer =3D kmalloc(req_size, GFP_KERNEL);
>+		if (ureq->req_buffer =3D=3D NULL)
You could also use if (!ureq->req_buffer)

> 			goto error;
>
>-		video->ureq[i].req =3D usb_ep_alloc_request(video->ep, GFP_KERNEL);
>-		if (video->ureq[i].req =3D=3D NULL)
>+		ureq->req =3D usb_ep_alloc_request(video->ep, GFP_KERNEL);
>+		if (ureq->req =3D=3D NULL)
> 			goto error;
>
>-		video->ureq[i].req->buf =3D video->ureq[i].req_buffer;
>-		video->ureq[i].req->length =3D 0;
>-		video->ureq[i].req->complete =3D uvc_video_complete;
>-		video->ureq[i].req->context =3D &video->ureq[i];
>-		video->ureq[i].video =3D video;
>-		video->ureq[i].last_buf =3D NULL;
>+		ureq->req->buf =3D ureq->req_buffer;
>+		ureq->req->length =3D 0;
>+		ureq->req->complete =3D uvc_video_complete;
>+		ureq->req->context =3D ureq;
>+		ureq->video =3D video;
>+		ureq->last_buf =3D 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 +496,8 @@ 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 =3D=3D NULL) {
> 		uvcg_info(&video->uvc->func,
>@@ -502,9 +509,10 @@ int uvcg_video_enable(struct uvc_video *video, int en=
able)
> 		cancel_work_sync(&video->pump);
> 		uvcg_queue_cancel(&video->queue, 0);
>
>-		for (i =3D 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 +544,7 @@ int uvcg_video_enable(struct uvc_video *video, int ena=
ble)
>  */
> 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);
>--
>2.42.0.609.gbb76f46606-goog
>
>

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