leds: lp5523: fix out-of-bounds bug in lp5523_selftest()

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.
Reported-by: Arne Staessen <a.staessen@televic.com>
Signed-off-by: Maarten Zanders <maarten.zanders@mind.be>
Signed-off-by: Pavel Machek <pavel@ucw.cz>

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)