[PATCH RFC v2] usb: gadget: uvc: check endpoint enabled state in uvcg_video_enable()

A NULL pointer dereference can occur in uvc_video_prep_requests() if
userspace issues a VIDIOC_STREAMON ioctl before the USB host has fully
configured the streaming endpoint.

When userspace calls VIDIOC_STREAMON, the driver handles it in
uvc_v4l2_streamon(), which in turn calls uvcg_video_enable(). Currently,
uvcg_video_enable() only checks if the endpoint pointer is allocated
(video->ep == NULL), but it fails to check if the endpoint is actually
enabled (video->ep->enabled).

The endpoint descriptor (video->ep->desc) is only assigned when the USB
host explicitly selects the streaming alternate setting via a SET_INTERFACE
control request. If userspace prematurely calls VIDIOC_STREAMON before the
host has selected the streaming alternate setting, video->ep->desc will
still be NULL.

Because uvcg_video_enable() does not verify the endpoint's enabled state,
it proceeds to call uvc_video_alloc_requests() and then
uvc_video_prep_requests(). Inside uvc_video_prep_requests(), the code
unconditionally dereferences video->ep->desc, resulting in a KASAN
null-ptr-deref / general protection fault:

Oops: general protection fault, probably for non-canonical address
0xdffffc0000000000: 0000 [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
RIP: 0010:usb_endpoint_xfer_isoc include/uapi/linux/usb/ch9.h:571 [inline]
RIP: 0010:uvc_video_prep_requests
drivers/usb/gadget/function/uvc_video.c:508 [inline]
RIP: 0010:uvc_video_alloc_requests
drivers/usb/gadget/function/uvc_video.c:559 [inline]
RIP: 0010:uvcg_video_enable+0x142/0xe70
drivers/usb/gadget/function/uvc_video.c:784
Call Trace:
 <TASK>
 uvc_v4l2_streamon+0x7e/0x110 drivers/usb/gadget/function/uvc_v4l2.c:531
 __video_do_ioctl+0x8af/0xc70 drivers/media/v4l2-core/v4l2-ioctl.c:3133
 video_usercopy+0x860/0x1430 drivers/media/v4l2-core/v4l2-ioctl.c:3475
 v4l2_ioctl+0x18d/0x1e0 drivers/media/v4l2-core/v4l2-dev.c:366
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583

To fix this, update uvcg_video_enable() to also verify that the endpoint is
enabled (!video->ep->enabled). This ensures that if userspace prematurely
calls VIDIOC_STREAMON, the driver will safely reject the request with
-ENODEV instead of crashing the kernel.

Fixes: 48dbe731171e ("usb: gadget: uvc: set req_size and n_requests based on the frame interval")
Assisted-by: Gemini:gemini-3.5-flash Gemini:gemini-3.1-pro-preview syzbot
Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=44835f0858f11e3e923c
Link: https://syzkaller.appspot.com/ai_job?id=e3902952-fe28-4ca4-a910-c485a9927925
To: "Greg Kroah-Hartman" <[email protected]>
To: <[email protected]>
To: "Michael Grzeschik" <[email protected]>
Cc: "Frank Li" <[email protected]>
Cc: "Jimmy Hu" <[email protected]>
Cc: "Hans Verkuil" <[email protected]>
Cc: "Kees Cook" <[email protected]>
Cc: "Laurent Pinchart" <[email protected]>
Cc: <[email protected]>
Cc: "Muhammad Bilal" <[email protected]>
Cc: "Junzhong Pan" <[email protected]>
Cc: "Xu Yang" <[email protected]>

---
v2:
- Check that uvc->state is UVC_STATE_CONNECTED in uvc_v4l2_streamon() before allowing streaming.
- Update uvc->state to UVC_STATE_STREAMING before calling uvcg_video_enable(), and revert it on failure.
- Check video->ep->desc in addition to video->ep->enabled in uvcg_video_enable().
- Add safety checks for video->ep, video->ep->enabled, and video->ep->desc in uvc_video_alloc_requests().

v1:
https://lore.kernel.org/all/[email protected]/T/
---
diff --git a/drivers/usb/gadget/function/uvc_v4l2.c b/drivers/usb/gadget/function/uvc_v4l2.c
index dfa0521a2..a80663c9a 100644
--- a/drivers/usb/gadget/function/uvc_v4l2.c
+++ b/drivers/usb/gadget/function/uvc_v4l2.c
@@ -527,17 +527,24 @@ uvc_v4l2_streamon(struct file *file, void *fh, enum v4l2_buf_type type)
 	if (type != video->queue.queue.type)
 		return -EINVAL;
 
+	if (uvc->state != UVC_STATE_CONNECTED)
+		return -ENODEV;
+
+	uvc->state = UVC_STATE_STREAMING;
+
 	/* Enable UVC video. */
 	ret = uvcg_video_enable(video);
-	if (ret < 0)
+	if (ret < 0) {
+		if (uvc->state == UVC_STATE_STREAMING)
+			uvc->state = UVC_STATE_CONNECTED;
 		return ret;
+	}
 
 	/*
 	 * Complete the alternate setting selection setup phase now that
 	 * userspace is ready to provide video frames.
 	 */
 	uvc_function_setup_continue(uvc, 0);
-	uvc->state = UVC_STATE_STREAMING;
 
 	return 0;
 }
diff --git a/drivers/usb/gadget/function/uvc_video.c b/drivers/usb/gadget/function/uvc_video.c
index 2f9700b3f..bd67a9d80 100644
--- a/drivers/usb/gadget/function/uvc_video.c
+++ b/drivers/usb/gadget/function/uvc_video.c
@@ -551,6 +551,9 @@ uvc_video_alloc_requests(struct uvc_video *video)
 	unsigned int i;
 	int ret = -ENOMEM;
 
+	if (video->ep == NULL || !video->ep->enabled || !video->ep->desc)
+		return -ENODEV;
+
 	/*
 	 * calculate in uvc_video_prep_requests
 	 * - video->uvc_num_requests
@@ -764,7 +767,7 @@ int uvcg_video_enable(struct uvc_video *video)
 {
 	int ret;
 
-	if (video->ep == NULL) {
+	if (video->ep == NULL || !video->ep->enabled || !video->ep->desc) {
 		uvcg_info(&video->uvc->func,
 			  "Video enable failed, device is uninitialized.\n");
 		return -ENODEV;


base-commit: db2ddb87143519e20a95aa36c60b36107b736a58
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