linux-kernel - Re: [PATCH v2] media: em28xx: add missing em28xx_close

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Date:   Thu, 29 Jul 2021 11:45:19 +0200
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Pavel Skripkin <paskripkin@...il.com>, mchehab@...nel.org
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzbot+a6969ef522a36d3344c9@...kaller.appspotmail.com
Subject: Re: [PATCH v2] media: em28xx: add missing em28xx_close_extension

On 21/07/2021 21:43, Pavel Skripkin wrote:
> If em28xx dev has ->dev_next pointer, we need to delete dev_next list node
> from em28xx_extension_devlist on disconnect to avoid UAF bugs and
> corrupted list bugs, since driver frees this pointer on disconnect.
> 
> Fixes: 1a23f81b7dc3 ("V4L/DVB (9979): em28xx: move usb probe code to a proper place")
> Reported-and-tested-by: syzbot+a6969ef522a36d3344c9@...kaller.appspotmail.com
> Signed-off-by: Pavel Skripkin <paskripkin@...il.com>
> ---
> 
> Changes in v2:
> 	Previous patch was completely broken. I've done some debugging
> 	again and found true root case of the reported bug.
> 
> ---
>  drivers/media/usb/em28xx/em28xx-cards.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/usb/em28xx/em28xx-cards.c b/drivers/media/usb/em28xx/em28xx-cards.c
> index c1e0dccb7408..d56b040e1bd7 100644
> --- a/drivers/media/usb/em28xx/em28xx-cards.c
> +++ b/drivers/media/usb/em28xx/em28xx-cards.c
> @@ -4139,8 +4139,10 @@ static void em28xx_usb_disconnect(struct usb_interface *intf)
>  
>  	em28xx_close_extension(dev);
>  
> -	if (dev->dev_next)
> +	if (dev->dev_next) {
>  		em28xx_release_resources(dev->dev_next);
> +		em28xx_close_extension(dev->dev_next);

Wouldn't it be better to swap these two?

That order is also used for em28xx_close_extension(dev) and em28xx_release_resources(dev).

You do need to store dev->dev_next in a temp variable, though.

Regards,

	Hans

> +	}
>  	em28xx_release_resources(dev);
>  
>  	if (dev->dev_next) {
>