linux-kernel - Re: [PATCH] leds: lp5523: fix out-of-bounds bug in lp5523

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Message-ID: <20221028153457.GA14936@duo.ucw.cz>
Date:   Fri, 28 Oct 2022 17:34:57 +0200
From:   Pavel Machek <pavel@....cz>
To:     Maarten Zanders <maarten.zanders@...d.be>
Cc:     Arne Staessen <a.staessen@...evic.com>, linux-leds@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] leds: lp5523: fix out-of-bounds bug in lp5523_selftest()

Hi!

> When not all LED channels of the led chip are configured, the
> sysfs selftest functionality gives erroneous results and tries to
> test all channels of the chip.
> There is a potential for LED overcurrent conditions since the
> test current will be set to values from out-of-bound regions.
> 
> It is wrong to use pdata->led_config[i].led_current to skip absent
> channels as led_config[] only contains the configured LED channels.
> 
> Instead of iterating over all the physical channels of the device,
> loop over the available LED configurations and use led->chan_nr to
> access the correct i2c registers. Keep the zero-check for the LED
> current as existing users might depend on this to disable a channel.

Thanks, applied, I'll push eventually.

I wonder, should we do these kind of actions on attribute _read_? I'd
preffer some kind of write action to trigger this.

Best regards,
								Pavel

> Reported-by: Arne Staessen <a.staessen@...evic.com>
> Signed-off-by: Maarten Zanders <maarten.zanders@...d.be>
> ---
>  drivers/leds/leds-lp5523.c | 27 +++++++++++++++------------
>  1 file changed, 15 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/leds/leds-lp5523.c b/drivers/leds/leds-lp5523.c
> index 369d40b0b65b..e08e3de1428d 100644
> --- a/drivers/leds/leds-lp5523.c
> +++ b/drivers/leds/leds-lp5523.c
> @@ -581,8 +581,8 @@ static ssize_t lp5523_selftest(struct device *dev,
>  	struct lp55xx_led *led = i2c_get_clientdata(to_i2c_client(dev));
>  	struct lp55xx_chip *chip = led->chip;
>  	struct lp55xx_platform_data *pdata = chip->pdata;
> -	int i, ret, pos = 0;
> -	u8 status, adc, vdd;
> +	int ret, pos = 0;
> +	u8 status, adc, vdd, i;
>  
>  	mutex_lock(&chip->lock);
>  
> @@ -612,20 +612,21 @@ static ssize_t lp5523_selftest(struct device *dev,
>  
>  	vdd--;	/* There may be some fluctuation in measurement */
>  
> -	for (i = 0; i < LP5523_MAX_LEDS; i++) {
> -		/* Skip non-existing channels */
> +	for (i = 0; i < pdata->num_channels; i++) {
> +		/* Skip disabled channels */
>  		if (pdata->led_config[i].led_current == 0)
>  			continue;
>  
>  		/* Set default current */
> -		lp55xx_write(chip, LP5523_REG_LED_CURRENT_BASE + i,
> +		lp55xx_write(chip, LP5523_REG_LED_CURRENT_BASE + led->chan_nr,
>  			pdata->led_config[i].led_current);
>  
> -		lp55xx_write(chip, LP5523_REG_LED_PWM_BASE + i, 0xff);
> +		lp55xx_write(chip, LP5523_REG_LED_PWM_BASE + led->chan_nr,
> +			     0xff);
>  		/* let current stabilize 2 - 4ms before measurements start */
>  		usleep_range(2000, 4000);
>  		lp55xx_write(chip, LP5523_REG_LED_TEST_CTRL,
> -			     LP5523_EN_LEDTEST | i);
> +			     LP5523_EN_LEDTEST | led->chan_nr);
>  		/* ADC conversion time is 2.7 ms typically */
>  		usleep_range(3000, 6000);
>  		ret = lp55xx_read(chip, LP5523_REG_STATUS, &status);
> @@ -633,20 +634,22 @@ static ssize_t lp5523_selftest(struct device *dev,
>  			goto fail;
>  
>  		if (!(status & LP5523_LEDTEST_DONE))
> -			usleep_range(3000, 6000);/* Was not ready. Wait. */
> +			usleep_range(3000, 6000); /* Was not ready. Wait. */
>  
>  		ret = lp55xx_read(chip, LP5523_REG_LED_TEST_ADC, &adc);
>  		if (ret < 0)
>  			goto fail;
>  
>  		if (adc >= vdd || adc < LP5523_ADC_SHORTCIRC_LIM)
> -			pos += sprintf(buf + pos, "LED %d FAIL\n", i);
> +			pos += sprintf(buf + pos, "LED %d FAIL\n",
> +				       led->chan_nr);
>  
> -		lp55xx_write(chip, LP5523_REG_LED_PWM_BASE + i, 0x00);
> +		lp55xx_write(chip, LP5523_REG_LED_PWM_BASE + led->chan_nr,
> +			     0x00);
>  
>  		/* Restore current */
> -		lp55xx_write(chip, LP5523_REG_LED_CURRENT_BASE + i,
> -			led->led_current);
> +		lp55xx_write(chip, LP5523_REG_LED_CURRENT_BASE + led->chan_nr,
> +			     led->led_current);
>  		led++;
>  	}
>  	if (pos == 0)
> -- 
> 2.37.3

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