power: supply: sbs-battery: Fix use-after-free in power_supply_changed()

Using the `devm_` variant for requesting IRQ _before_ the `devm_`
variant for allocating/registering the `power_supply` handle, means that
the `power_supply` handle will be deallocated/unregistered _before_ the
interrupt handler (since `devm_` naturally deallocates in reverse
allocation order). This means that during removal, there is a race
condition where an interrupt can fire just _after_ the `power_supply`
handle has been freed, *but* just _before_ the corresponding
unregistration of the IRQ handler has run.

This will lead to the IRQ handler calling `power_supply_changed()` with
a freed `power_supply` handle. Which usually crashes the system or
otherwise silently corrupts the memory...

Note that there is a similar situation which can also happen during
`probe()`; the possibility of an interrupt firing _before_ registering
the `power_supply` handle. This would then lead to the nasty situation
of using the `power_supply` handle *uninitialized* in
`power_supply_changed()`.

Fix this racy use-after-free by making sure the IRQ is requested _after_
the registration of the `power_supply` handle. Keep the old behavior of
just printing a warning in case of any failures during the IRQ request
and finishing the probe successfully.

Fixes: d2cec82c2880 ("power: sbs-battery: Request threaded irq and fix dev callback cookie")
Signed-off-by: Waqar Hameed <[e-mail]>
Reviewed-by: Phil Reid <[e-mail]>
Link: https://patch.msgid.link/0ef8[e-mail]
Signed-off-by: Sebastian Reichel <[e-mail]>

drivers/power/supply/sbs-battery.c

···
 
 	i2c_set_clientdata(client, chip);
 
-	if (!chip->gpio_detect)
-		goto skip_gpio;
-
-	irq = gpiod_to_irq(chip->gpio_detect);
-	if (irq <= 0) {
-		dev_warn(&client->dev, "Failed to get gpio as irq: %d\n", irq);
-		goto skip_gpio;
-	}
-
-	rc = devm_request_threaded_irq(&client->dev, irq, NULL, sbs_irq,
-		IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING | IRQF_ONESHOT,
-		dev_name(&client->dev), chip);
-	if (rc) {
-		dev_warn(&client->dev, "Failed to request irq: %d\n", rc);
-		goto skip_gpio;
-	}
-
-skip_gpio:
 	/*
 	 * Before we register, we might need to make sure we can actually talk
 	 * to the battery.
···
 		return dev_err_probe(&client->dev, PTR_ERR(chip->power_supply),
 				     "Failed to register power supply\n");
 
+	if (!chip->gpio_detect)
+		goto out;
+
+	irq = gpiod_to_irq(chip->gpio_detect);
+	if (irq <= 0) {
+		dev_warn(&client->dev, "Failed to get gpio as irq: %d\n", irq);
+		goto out;
+	}
+
+	rc = devm_request_threaded_irq(&client->dev, irq, NULL, sbs_irq,
+		IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING | IRQF_ONESHOT,
+		dev_name(&client->dev), chip);
+	if (rc) {
+		dev_warn(&client->dev, "Failed to request irq: %d\n", rc);
+		goto out;
+	}
+
+out:
 	dev_info(&client->dev,
 		"%s: battery gas gauge device registered\n", client->name);