[PATCH 1/2] media: uvcvideo: Fix NULL deref on events for uninitialized controls

[Wei Jie Law]

A null-ptr-deref exists in v6.12.105 and upstream. KASAN crash log:

  KASAN: null-ptr-deref in range [0x0000000000000080-0x0000000000000087]
  Workqueue: events uvc_ctrl_status_event_work
  RIP: 0010:uvc_ctrl_status_event+0x105/0x280
   uvc_ctrl_status_event_work+0x82/0x240
   process_one_work+0x66f/0x10b0

XU controls are initialized lazily, on the first UVCIOC_CTRL_MAP or
UVCIOC_CTRL_QUERY.  Until then ctrl->info is all zeroes, so
info.mappings is not a valid list head, list_empty() returns false, and
uvc_ctrl_status_event() walks it from a NULL next pointer.

Fixes: e5225c820c05 ("media: uvcvideo: Send a control event when a Control Change interrupt arrives")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Wei Jie Law <98lawweijie@xxxxxxxxx>
Assisted-by: Claude:claude-opus-5
---
 drivers/media/usb/uvc/uvc_ctrl.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
index 3ca108b83f1d..21802f9b1b61 100644
--- a/drivers/media/usb/uvc/uvc_ctrl.c
+++ b/drivers/media/usb/uvc/uvc_ctrl.c
@@ -2209,7 +2209,12 @@ bool uvc_ctrl_status_event_async(struct urb *urb, struct uvc_video_chain *chain,
 	struct uvc_device *dev = chain->dev;
 	struct uvc_ctrl_work *w = &dev->async_ctrl;
 
-	if (list_empty(&ctrl->info.mappings))
+	/*
+	 * An uninitialized control has a zeroed info struct, so its
+	 * mappings list head is not a list: list_empty() returns false
+	 * and the walk dereferences NULL.
+	 */
+	if (!ctrl->initialized || list_empty(&ctrl->info.mappings))
 		return false;
 
 	w->data = data;
-- 
2.43.0