[PATCH v2 1/2] usb: gadget: uvc: Fix use are free during STREAMOFF

[Avichal Rakesh <arakesh@google.com>]

There is a path that may lead to freed memory being referenced,
causing kernel panics.

The kernel panic has the following stack trace:

Workqueue: uvcgadget uvcg_video_pump.c51fb85fece46625450f86adbf92c56c.cfi_jt
pstate: 60c00085 (nZCv daIf +PAN +UAO -TCO BTYPE=--)
pc : __list_del_entry_valid+0xc0/0xd4
lr : __list_del_entry_valid+0xc0/0xd4
Call trace:
  __list_del_entry_valid+0xc0/0xd4
  uvc_video_free_request+0x60/0x98
  uvcg_video_pump+0x1cc/0x204
  process_one_work+0x21c/0x4b8
  worker_thread+0x29c/0x574
  kthread+0x158/0x1b0
  ret_from_fork+0x10/0x30

The root cause is that uvcg_video_usb_req_queue frees the uvc_request
if is_enabled is false and returns an error status. video_pump also
frees the associated request if uvcg_video_usb_req_queue returns an
error status, leading to double free and accessing garbage memory.

To fix the issue, this patch removes freeing logic from
uvcg_video_usb_req_queue, and lets the callers to the function handle
queueing errors as they see fit.

Fixes: 6acba0345b68 ("usb:gadget:uvc Do not use worker thread to pump isoc usb requests")
Tested-by: Avichal Rakesh <arakesh@google.com>
Signed-off-by: Avichal Rakesh <arakesh@google.com>
---
v1 -> v2: Address review comment; add "Fixes" tag; fix goofy line wrap

 drivers/usb/gadget/function/uvc_video.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/gadget/function/uvc_video.c b/drivers/usb/gadget/function/uvc_video.c
index 98ba524c27f5..7f18dc471be3 100644
--- a/drivers/usb/gadget/function/uvc_video.c
+++ b/drivers/usb/gadget/function/uvc_video.c
@@ -276,10 +276,9 @@ static int uvcg_video_usb_req_queue(struct uvc_video *video,
 	bool is_bulk = video->max_payload_size;
 	struct list_head *list = NULL;

-	if (!video->is_enabled) {
-		uvc_video_free_request(req->context, video->ep);
+	if (!video->is_enabled)
 		return -ENODEV;
-	}
+
 	if (queue_to_ep) {
 		struct uvc_request *ureq = req->context;
 		/*
@@ -464,8 +463,15 @@ uvc_video_complete(struct usb_ep *ep, struct usb_request *req)
 		 * and this thread for isoc endpoints.
 		 */
 		ret = uvcg_video_usb_req_queue(video, to_queue, !is_bulk);
-		if (ret < 0)
+		if (ret < 0) {
+			/*
+			 * Endpoint error, but the stream is still enabled.
+			 * Put request back in req_free for it to be cleaned
+			 * up later.
+			 */
 			uvcg_queue_cancel(queue, 0);
+			list_add_tail(&to_queue->list, &video->req_free);
+		}
 	} else {
 		uvc_video_free_request(ureq, ep);
 	}
--
2.43.0.472.g3155946c3a-goog