[PATCH v3 3/3] usb: gadget: uvc: Fix use-after-free for inflight usb_requests

[Avichal Rakesh <arakesh@google.com>]

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 is patch 2 of 2 in fixing the use-after-free issue. It adds a new
flag to uvc_request to mark it as 'abandoned'. When disabling the video
stream, instead of de-allocating all uvc_requests and usb_requests, the
gadget driver only de-allocates those usb_requests that are currently
owned by the gadget driver (as present in req_free). Other usb_requests
have their corresponding 'is_abandoned' flag tripped, and the
usb_requests complete handler takes care of freeing the usb_request and
its corresponding uvc_request.

This should ensure that uvc gadget driver never accidentally de-allocates
a usb_request that it doesn't own.

Link: https://lore.kernel.org/7cd81649-2795-45b6-8c10-b7df1055020d@google.com
Suggested-by: Michael Grzeschik <mgr@pengutronix.de>
Signed-off-by: Avichal Rakesh <arakesh@google.com>
---
v1 -> v2: Rebased to ToT, and fixed deadlock reported in
          https://lore.kernel.org/all/ZRv2UnKztgyqk2pt@pengutronix.de/
v2 -> v3: Fix email threading goof-up

 drivers/usb/gadget/function/uvc.h       |   1 +
 drivers/usb/gadget/function/uvc_video.c | 118 ++++++++++++++++++++----
 2 files changed, 102 insertions(+), 17 deletions(-)

diff --git a/drivers/usb/gadget/function/uvc.h b/drivers/usb/gadget/function/uvc.h
index 993694da0bbc..e69cfb7cced1 100644
--- a/drivers/usb/gadget/function/uvc.h
+++ b/drivers/usb/gadget/function/uvc.h
@@ -82,6 +82,7 @@ struct uvc_request {
 	u8 header[UVCG_REQUEST_HEADER_LEN];
 	struct uvc_buffer *last_buf;
 	struct list_head list;
+	bool is_abandoned;
 };

 struct uvc_video {
diff --git a/drivers/usb/gadget/function/uvc_video.c b/drivers/usb/gadget/function/uvc_video.c
index 3c4d286d81c0..69521886d599 100644
--- a/drivers/usb/gadget/function/uvc_video.c
+++ b/drivers/usb/gadget/function/uvc_video.c
@@ -271,7 +271,21 @@ uvc_video_complete(struct usb_ep *ep, struct usb_request *req)
 	struct uvc_video *video = ureq->video;
 	struct uvc_video_queue *queue = &video->queue;
 	struct uvc_device *uvc = video->uvc;
+	struct uvc_buffer *last_buf;
 	unsigned long flags;
+	bool is_abandoned;
+
+	spin_lock_irqsave(&video->req_lock, flags);
+	is_abandoned = ureq->is_abandoned;
+	last_buf = ureq->last_buf;
+	ureq->last_buf = NULL;
+	spin_unlock_irqrestore(&video->req_lock, flags);
+
+	if (is_abandoned) {
+		uvcg_dbg(&video->uvc->func, "Freeing abandoned usb_request\n");
+		uvc_video_free_request(ureq, ep);
+		return;
+	}

 	if (uvc->state == UVC_STATE_CONNECTED) {
 		usb_ep_free_request(video->ep, ureq->req);
@@ -300,15 +314,29 @@ uvc_video_complete(struct usb_ep *ep, struct usb_request *req)
 		uvcg_queue_cancel(queue, 0);
 	}

-	if (ureq->last_buf) {
-		uvcg_complete_buffer(&video->queue, ureq->last_buf);
-		ureq->last_buf = NULL;
+	if (last_buf) {
+		spin_lock_irqsave(&video->queue.irqlock, flags);
+		uvcg_complete_buffer(&video->queue, last_buf);
+		spin_unlock_irqrestore(&video->queue.irqlock, flags);
 	}

+	/*
+	 * request might have been abandoned while being processed.
+	 * do a last minute check before queueing the request back.
+	 */
 	spin_lock_irqsave(&video->req_lock, flags);
-	list_add_tail(&req->list, &video->req_free);
+	is_abandoned = ureq->is_abandoned;
+	if (!is_abandoned)
+		list_add_tail(&req->list, &video->req_free);
 	spin_unlock_irqrestore(&video->req_lock, flags);

+	if (is_abandoned) {
+		uvcg_dbg(&video->uvc->func,
+			 "usb_request abandoned mid-processing - freeing.\n");
+		uvc_video_free_request(ureq, ep);
+		return;
+	}
+
 	if (uvc->state == UVC_STATE_STREAMING)
 		queue_work(video->async_wq, &video->pump);
 }
@@ -372,7 +400,6 @@ uvc_video_alloc_requests(struct uvc_video *video)
 	}

 	video->req_size = req_size;
-
 	return 0;

 error:
@@ -504,13 +531,80 @@ static void uvcg_video_pump(struct work_struct *work)
 	return;
 }

+/*
+ * Disable video stream. This ensures that any inflight usb requests are marked
+ * for clean up and all video buffers are dropped before returning.
+ */
+static void uvcg_video_disable(struct uvc_video *video)
+{
+	struct uvc_buffer *buf, *tmp_buf;
+	struct uvc_request *ureq, *temp;
+	struct list_head buf_list; /* track in-flight video buffers */
+	struct usb_request *req;
+	unsigned long flags;
+
+	INIT_LIST_HEAD(&buf_list);
+
+	cancel_work_sync(&video->pump);
+	uvcg_queue_cancel(&video->queue, 0);
+
+	list_for_each_entry(ureq, &video->ureqs, list) {
+		if (ureq->req)
+			usb_ep_dequeue(video->ep, ureq->req);
+	}
+
+	/**
+	 * acquiring req_lock here should prevent any more complete
+	 * callbacks from processing until we've abandoned the
+	 * requests that are still in-flight and let the complete
+	 * callback handle cleanup
+	 */
+	spin_lock_irqsave(&video->req_lock, flags);
+	/* abandon all usb requests */
+	list_for_each_entry_safe(ureq, temp, &video->ureqs, list) {
+		ureq->is_abandoned = true;
+		if (ureq->last_buf) {
+			list_add(&ureq->last_buf->queue, &buf_list);
+			ureq->last_buf = NULL;
+		}
+		list_del_init(&ureq->list);
+	}
+	/*
+	 * re-add uvc_requests currently owned by the gadget to
+	 * video->ureqs to be deallocated. This effectively leaves
+	 * video->ureqs with the requests that we currently own.
+	 */
+	list_for_each_entry(req, &video->req_free, list) {
+		ureq = req->context;
+		list_add_tail(&ureq->list, &video->ureqs);
+	}
+	spin_unlock_irqrestore(&video->req_lock, flags);
+
+	/*
+	 * drop abandoned uvc_buffers, as the completion handler
+	 * no longer will
+	 */
+	if (!list_empty(&buf_list)) {
+		spin_lock_irqsave(&video->queue.irqlock, flags);
+		list_for_each_entry_safe(buf, tmp_buf,
+						&buf_list, queue) {
+			video->queue.flags |= UVC_QUEUE_DROP_INCOMPLETE;
+			uvcg_complete_buffer(&video->queue, buf);
+			list_del(&buf->queue);
+		}
+		spin_unlock_irqrestore(&video->queue.irqlock, flags);
+	}
+
+	uvc_video_free_requests(video);
+	uvcg_queue_enable(&video->queue, 0);
+}
+
 /*
  * Enable or disable the video stream.
  */
 int uvcg_video_enable(struct uvc_video *video, int enable)
 {
 	struct uvc_device *uvc = video->uvc;
-	struct uvc_request *ureq;
 	int ret;

 	if (video->ep == NULL) {
@@ -521,17 +615,7 @@ int uvcg_video_enable(struct uvc_video *video, int enable)

 	if (!enable) {
 		uvc->state = UVC_STATE_CONNECTED;
-
-		cancel_work_sync(&video->pump);
-		uvcg_queue_cancel(&video->queue, 0);
-
-		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);
+		uvcg_video_disable(video);
 		return 0;
 	}

--
2.42.0.609.gbb76f46606-goog