In the Linux kernel, the following vulnerability has been resolved: backlight: led-bl: Add devlink to supplier LEDs LED Backlight is a consumer of one or multiple LED class devices, but devlink is currently unable to create correct sup…

Overview

In the Linux kernel, the following vulnerability has been resolved:

backlight: led-bl: Add devlink to supplier LEDs

LED Backlight is a consumer of one or multiple LED class devices, but devlink is currently unable to create correct supplier-producer links when the supplier is a class device. It creates instead a link where the supplier is the parent of the expected device.

One consequence is that removal order is not correctly enforced.

Issues happen for example with the following sections in a device tree overlay:

// An LED driver chip
pca9632@62 {
    compatible = "nxp,pca9632";
    reg = <0x62>;

// ...

    addon_led_pwm: led-pwm@3 {
        reg = <3>;
        label = "addon:led:pwm";
    };
};

backlight-addon {
    compatible = "led-backlight";
    leds = <&addon_led_pwm>;
    brightness-levels = <255>;
    default-brightness-level = <255>;
};

In this example, the devlink should be created between the backlight-addon (consumer) and the pca9632@62 (supplier). Instead it is created between the backlight-addon (consumer) and the parent of the pca9632@62, which is typically the I2C bus adapter.

On removal of the above overlay, the LED driver can be removed before the backlight device, resulting in:

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000010
...
Call trace:
 led_put+0xe0/0x140
 devm_led_release+0x6c/0x98

Another way to reproduce the bug without any device tree overlays is unbinding the LED class device (pca9632@62) before unbinding the consumer (backlight-addon):

echo 11-0062 >/sys/bus/i2c/drivers/leds-pca963x/unbind echo ...backlight-dock >/sys/bus/platform/drivers/led-backlight/unbind

Fix by adding a devlink between the consuming led-backlight device and the supplying LED device, as other drivers and subsystems do as well.

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.