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

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Message-ID: <20260111153156.GA4474@pendragon.ideasonboard.com>
Date: Sun, 11 Jan 2026 17:31:56 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Edward Adam Davis <eadavis@...com>
Cc: syzbot+16062f26c6480975e5ed@...kaller.appspotmail.com,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	mchehab@...nel.org, sakari.ailus@...ux.intel.com,
	syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH 1/2] media: em28xx-video: add the unregister of video/VBI
 entity

On Sun, Jan 11, 2026 at 01:29:10PM +0800, 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].

You have no idea what this means, do you ?

> 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@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=16062f26c6480975e5ed
> Tested-by: syzbot+16062f26c6480975e5ed@...kaller.appspotmail.com
> Signed-off-by: Edward Adam Davis <eadavis@...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);
>  #endif
>  }
>  

-- 
Regards,

Laurent Pinchart