linux-kernel - Re: [PATCH 1/2] gpio: fix NULL-deref-on-deregistration regression

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Message-ID: <YDypfjoBpHsd+dCo@hovoldconsulting.com>
Date:   Mon, 1 Mar 2021 09:44:46 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzbot+d27b4c8adbbff70fbfde@...kaller.appspotmail.com
Subject: Re: [PATCH 1/2] gpio: fix NULL-deref-on-deregistration regression

On Fri, Feb 26, 2021 at 01:54:12PM -0800, Saravana Kannan wrote:
> On Fri, Feb 26, 2021 at 6:55 AM Johan Hovold <johan@...nel.org> wrote:
> >
> > Fix a NULL-pointer deference when deregistering the gpio character
> > device that was introduced by the recent stub-driver hack. When the new
> > "driver" is unbound as part of deregistration, driver core clears the
> > driver-data pointer which is used to retrieve the struct gpio_device in
> > its release callback.
> >
> > Fix this by using container_of() in the release callback as should have
> > been done all along.
> >
> > Fixes: 4731210c09f5 ("gpiolib: Bind gpio_device to a driver to enable fw_devlink=on by default")
> > Cc: Saravana Kannan <saravanak@...gle.com>
> > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > Reported-by: syzbot+d27b4c8adbbff70fbfde@...kaller.appspotmail.com
> > Signed-off-by: Johan Hovold <johan@...nel.org>
> > ---
> >  drivers/gpio/gpiolib.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> > index adf55db080d8..e1016bc8cf14 100644
> > --- a/drivers/gpio/gpiolib.c
> > +++ b/drivers/gpio/gpiolib.c
> > @@ -474,7 +474,7 @@ EXPORT_SYMBOL_GPL(gpiochip_line_is_valid);
> >
> >  static void gpiodevice_release(struct device *dev)
> >  {
> > -       struct gpio_device *gdev = dev_get_drvdata(dev);
> > +       struct gpio_device *gdev = container_of(dev, struct gpio_device, dev);
> 
> Can you also delete the dev_set_drvdata() in
> gpiochip_add_data_with_key() if the drvdata is not used
> elsewhere anymore? I skimmed the code and it doesn't look like it, but
> I could be wrong.

Yeah, I considered it but didn't want to risk introducing any new
regressions just to clean up a redundant store.

But looking at it again today, I agree that it looks like it isn't used
anywhere else. I'll send a v2. Thanks.

Johan