[PATCH 0/2] gpio: regression fixes

[PATCH 0/2] gpio: regression fixes

[Johan Hovold]

Here's a fix for a regression in 5.12 due to the new stub-driver hack,
and a fix for potential list corruption due to missing locking which has
been there since the introduction of the character-device interface in
4.6.

Johan


Johan Hovold (2):
  gpio: fix NULL-deref-on-deregistration regression
  gpio: fix gpio-device list corruption

 drivers/gpio/gpiolib.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

-- 
2.26.2

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

[Johan Hovold]

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@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reported-by: syzbot+d27b4c8adbbff70fbfde@syzkaller.appspotmail.com
Signed-off-by: Johan Hovold <johan@kernel.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);
 
 	list_del(&gdev->list);
 	ida_free(&gpio_ida, gdev->id);
-- 
2.26.2

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

[Saravana Kannan]

On Fri, Feb 26, 2021 at 6:55 AM Johan Hovold <johan@kernel.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@google.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Reported-by: syzbot+d27b4c8adbbff70fbfde@syzkaller.appspotmail.com
> Signed-off-by: Johan Hovold <johan@kernel.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.

-Saravana

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

[Johan Hovold]

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@kernel.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@google.com>
> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Reported-by: syzbot+d27b4c8adbbff70fbfde@syzkaller.appspotmail.com
> > Signed-off-by: Johan Hovold <johan@kernel.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

[PATCH 2/2] gpio: fix gpio-device list corruption

[Johan Hovold]

Make sure to hold the gpio_lock when removing the gpio device from the
gpio_devices list (when dropping the last reference) to avoid corrupting
the list when there are concurrent accesses.

Fixes: ff2b13592299 ("gpio: make the gpiochip a real device")
Cc: stable@vger.kernel.org      # 4.6
Signed-off-by: Johan Hovold <johan@kernel.org>
---
 drivers/gpio/gpiolib.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index e1016bc8cf14..42bdc55a15f9 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -475,8 +475,12 @@ EXPORT_SYMBOL_GPL(gpiochip_line_is_valid);
 static void gpiodevice_release(struct device *dev)
 {
 	struct gpio_device *gdev = container_of(dev, struct gpio_device, dev);
+	unsigned long flags;
 
+	spin_lock_irqsave(&gpio_lock, flags);
 	list_del(&gdev->list);
+	spin_unlock_irqrestore(&gpio_lock, flags);
+
 	ida_free(&gpio_ida, gdev->id);
 	kfree_const(gdev->label);
 	kfree(gdev->descs);
-- 
2.26.2

Re: [PATCH 2/2] gpio: fix gpio-device list corruption

[Saravana Kannan]

On Fri, Feb 26, 2021 at 6:55 AM Johan Hovold <johan@kernel.org> wrote:
>
> Make sure to hold the gpio_lock when removing the gpio device from the
> gpio_devices list (when dropping the last reference) to avoid corrupting
> the list when there are concurrent accesses.
>
> Fixes: ff2b13592299 ("gpio: make the gpiochip a real device")
> Cc: stable@vger.kernel.org      # 4.6
> Signed-off-by: Johan Hovold <johan@kernel.org>
> ---
>  drivers/gpio/gpiolib.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index e1016bc8cf14..42bdc55a15f9 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -475,8 +475,12 @@ EXPORT_SYMBOL_GPL(gpiochip_line_is_valid);
>  static void gpiodevice_release(struct device *dev)
>  {
>         struct gpio_device *gdev = container_of(dev, struct gpio_device, dev);
> +       unsigned long flags;
>
> +       spin_lock_irqsave(&gpio_lock, flags);
>         list_del(&gdev->list);
> +       spin_unlock_irqrestore(&gpio_lock, flags);
> +

Reviewed-by: Saravana Kannan <saravanak@google.com>

-Saravana

>         ida_free(&gpio_ida, gdev->id);
>         kfree_const(gdev->label);
>         kfree(gdev->descs);
> --
> 2.26.2
>