power: supply: bq256xx: 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.

Fixes: 32e4978 ("power: supply: bq256xx: Introduce the BQ256XX charger driver")
Signed-off-by: Waqar Hameed <waqar.hameed@axis.com>
Link: https://patch.msgid.link/39da6da8cc060fa0382ca859f65071e791cb6119.1766268280.git.waqar.hameed@axis.com
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

Author: whame

drivers/power/supply/bq256xx_charger.c

@@ -1740,6 +1740,12 @@ static int bq256xx_probe(struct i2c_client *client)
 		usb_register_notifier(bq->usb3_phy, &bq->usb_nb);
 	}
 
+	ret = bq256xx_power_supply_init(bq, &psy_cfg, dev);
+	if (ret) {
+		dev_err(dev, "Failed to register power supply\n");
+		return ret;
+	}
+
 	if (client->irq) {
 		ret = devm_request_threaded_irq(dev, client->irq, NULL,
 						bq256xx_irq_handler_thread,
@@ -1752,12 +1758,6 @@ static int bq256xx_probe(struct i2c_client *client)
 		}
 	}
 
-	ret = bq256xx_power_supply_init(bq, &psy_cfg, dev);
-	if (ret) {
-		dev_err(dev, "Failed to register power supply\n");
-		return ret;
-	}
-
 	ret = bq256xx_hw_init(bq);
 	if (ret) {
 		dev_err(dev, "Cannot initialize the chip.\n");