On Sun, 27 Oct 2024, Jacek Anaszewski wrote:
> Hi Mukesh,
>
> On 10/25/24 19:11, Mukesh Ojha wrote:
> > There is NULL pointer issue observed if from Process A where hid device
> > being added which results in adding a led_cdev addition and later a
> > another call to access of led_cdev attribute from Process B can result
> > in NULL pointer issue.
> >
> > Use mutex led_cdev->led_access to protect access to led->cdev and its
> > attribute inside brightness_show() and max_brightness_show() and also
> > update the comment for mutex that it should be used to protect the led
> > class device fields.
[...]
> > Signed-off-by: Mukesh Ojha <quic_mojha@xxxxxxxxxxx>
> > ---
> > Changes in v2:
> > - Updated the comment for led_access mutex lock.
> > - Also added mutex protection for max_brightness_show().
> >
> > drivers/leds/led-class.c | 14 +++++++++++---
> > include/linux/leds.h | 2 +-
> > 2 files changed, 12 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
> > index 06b97fd49ad9..f69f4e928d61 100644
> > --- a/drivers/leds/led-class.c
> > +++ b/drivers/leds/led-class.c
> > @@ -29,11 +29,14 @@ static ssize_t brightness_show(struct device *dev,
> > struct device_attribute *attr, char *buf)
> > {
> > struct led_classdev *led_cdev = dev_get_drvdata(dev);
> > + unsigned int brightness;
> > - /* no lock needed for this */
> > + mutex_lock(&led_cdev->led_access);
> > led_update_brightness(led_cdev);
> > + brightness = led_cdev->brightness;
> > + mutex_unlock(&led_cdev->led_access);
> > - return sprintf(buf, "%u\n", led_cdev->brightness);
> > + return sprintf(buf, "%u\n", brightness);
> > }
> > static ssize_t brightness_store(struct device *dev,
> > @@ -70,8 +73,13 @@ static ssize_t max_brightness_show(struct device *dev,
> > struct device_attribute *attr, char *buf)
> > {
> > struct led_classdev *led_cdev = dev_get_drvdata(dev);
> > + unsigned int max_brightness;
> > +
> > + mutex_lock(&led_cdev->led_access);
> > + max_brightness = led_cdev->max_brightness;
> > + mutex_unlock(&led_cdev->led_access);
> > - return sprintf(buf, "%u\n", led_cdev->max_brightness);
> > + return sprintf(buf, "%u\n", max_brightness);
> > }
> > static DEVICE_ATTR_RO(max_brightness);
> > diff --git a/include/linux/leds.h b/include/linux/leds.h
> > index e5968c3ed4ae..3524634fcc47 100644
> > --- a/include/linux/leds.h
> > +++ b/include/linux/leds.h
> > @@ -238,7 +238,7 @@ struct led_classdev {
> > struct kernfs_node *brightness_hw_changed_kn;
> > #endif
> > - /* Ensures consistent access to the LED Flash Class device */
> > + /* Ensures consistent access to the LED Class device */
>
> Nit: It was improper in the original comment as well:
>
> s/Class/class/
Some things can't be unseen. Please submit v3.
--
Lee Jones [李琼斯]
