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

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Date:   Thu, 29 Jul 2021 15:45:56 +0300
From:   Pavel Skripkin <paskripkin@...il.com>
To:     Hans Verkuil <hverkuil@...all.nl>
Cc:     mchehab@...nel.org, 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 Thu, 29 Jul 2021 11:45:19 +0200
Hans Verkuil <hverkuil@...all.nl> wrote:

> 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.
> 

Hi, Hans!

I don't understand why I need to store dev->dev_next in a temp
variable. I don't see code in em28xx_release_resources() or
em28xx_close_extension() that zeroes this pointer.



With regards,
Pavel Skripkin