Re: [PATCH 1/2] media: em28xx-video: add the unregister of video/VBI entity

Hans Verkuil
2026-03-16T14:03:27Z

On 11/01/2026 06:29, Edward Adam Davis wrote:
> When creating a media graph, a failure occurred due to the lack of
> a corresponding decoder. During the subsequent media device release
> process, the video and VBI devices were not properly unregistered,
> leading to a use-after-free vulnerability reported by syzbot [1].
>
> The fix involves adding the necessary unregister operations.
>
> [1]
> BUG: KASAN: slab-use-after-free in media_device_unregister+0x141/0x430 drivers/media/mc/mc-device.c:804
> Read of size 8 at addr ffff88807c114210 by task kworker/1:9/6093
> Call Trace:
> media_device_unregister+0x141/0x430 drivers/media/mc/mc-device.c:804
> em28xx_unregister_media_device drivers/media/usb/em28xx/em28xx-cards.c:3511 [inline]
> em28xx_release_resources+0xac/0x240 drivers/media/usb/em28xx/em28xx-cards.c:3532
> em28xx_usb_disconnect+0x19f/0x2f0 drivers/media/usb/em28xx/em28xx-cards.c:4201
> usb_unbind_interface+0x26e/0x910 drivers/usb/core/driver.c:458
>
> Allocated by task 5932:
> em28xx_v4l2_init+0x10b/0x2e70 drivers/media/usb/em28xx/em28xx-video.c:2532
> em28xx_init_extension+0x120/0x1c0 drivers/media/usb/em28xx/em28xx-core.c:1117
>
> Freed by task 5932:
> em28xx_free_v4l2 drivers/media/usb/em28xx/em28xx-video.c:2118 [inline]
> kref_put include/linux/kref.h:65 [inline]
> em28xx_v4l2_init+0x1683/0x2e70 drivers/media/usb/em28xx/em28xx-video.c:2901
>
> Reported-by: syzbot+16062f26c6480975e5ed@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=16062f26c6480975e5ed
> Tested-by: syzbot+16062f26c6480975e5ed@syzkaller.appspotmail.com
> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
> ---
> drivers/media/usb/em28xx/em28xx-video.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/media/usb/em28xx/em28xx-video.c b/drivers/media/usb/em28xx/em28xx-video.c
> index 2dfa3242a7ab..45b68ebf2e9c 100644
> --- a/drivers/media/usb/em28xx/em28xx-video.c
> +++ b/drivers/media/usb/em28xx/em28xx-video.c
> @@ -882,9 +882,12 @@ static void em28xx_v4l2_media_release(struct em28xx *dev)
>
> for (i = 0; i < MAX_EM28XX_INPUT; i++) {
> if (!INPUT(i)->type)
> - return;
> + break;
> media_device_unregister_entity(&dev->input_ent[i]);
> }
> + media_device_unregister_entity(&dev->v4l2->vdev.entity);
> + if (em28xx_vbi_supported(dev))
> + media_device_unregister_entity(&dev->v4l2->vbi_dev.entity);

This is definitely wrong: these are registered and unregistered in v4l2-dev.c,
so it makes no sense to unregister them here.

This is a very complicated driver, and fixing life-time issues is very hard.

Regards,

Hans

> #endif
> }
>