linux-kernel - Re: [syzbot] KASAN: use-after-free Read in em28xx_close

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Date:   Wed, 28 Jul 2021 16:39:13 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Hillf Danton <hdanton@...a.com>
Cc:     syzbot <syzbot+005037419ebdf14e1d87@...kaller.appspotmail.com>,
        igormtorrente@...il.com, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] KASAN: use-after-free Read in em28xx_close_extension

On Tue, Jul 27, 2021 at 05:14:55PM +0300, Dan Carpenter wrote:
> On Tue, Jul 27, 2021 at 06:01:51PM +0800, Hillf Danton wrote:
> > Along the probe path,
> > 
> > em28xx_usb_probe
> >   dev = kzalloc(sizeof(*dev), GFP_KERNEL);
> >   retval = em28xx_init_dev(dev, udev, intf, nr);
> >     em28xx_init_extension(dev);
> >       em28xx_ir_init(struct em28xx *dev)
> >         kref_get(&dev->ref);
> > 
> >   kref_init(&dev->ref);
> 
> Good detective work.
> 
> I've created a Smatch check to try find these.  It uses the fact that
> Smatch creates a bunch of fake assignments to set all the struct members
> of "dev" to zero.  Then it uses the modification hook to find the
> kref_init().  Those are sort of new uses for those hooks so that's quite
> fun.
> 
> I'll test it out overnight and see how it works.

My Smatch check didn't find any other bugs, but it only had 3 false
positives so I'll keep running it nightly on new code.

regards,
dan carpenter