power: supply: pm8916_bms_vm: 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: 098bce1 ("power: supply: Add pm8916 VM-BMS support")
Signed-off-by: Waqar Hameed <waqar.hameed@axis.com>
Reviewed-by: Nikita Travkin <nikita@trvn.ru>
Link: https://patch.msgid.link/2749c09ff81fcac87ae48147e216135450d8c067.1766268280.git.waqar.hameed@axis.com
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

Author: whame

drivers/power/supply/pm8916_bms_vm.c

@@ -167,15 +167,6 @@ static int pm8916_bms_vm_battery_probe(struct platform_device *pdev)
 	if (ret < 0)
 		return -EINVAL;
 
-	irq = platform_get_irq_byname(pdev, "fifo");
-	if (irq < 0)
-		return irq;
-
-	ret = devm_request_threaded_irq(dev, irq, NULL, pm8916_bms_vm_fifo_update_done_irq,
-					IRQF_ONESHOT, "pm8916_vm_bms", bat);
-	if (ret)
-		return ret;
-
 	ret = regmap_bulk_read(bat->regmap, bat->reg + PM8916_PERPH_TYPE, &tmp, 2);
 	if (ret)
 		goto comm_error;
@@ -220,6 +211,15 @@ static int pm8916_bms_vm_battery_probe(struct platform_device *pdev)
 	if (ret)
 		return dev_err_probe(dev, ret, "Unable to get battery info\n");
 
+	irq = platform_get_irq_byname(pdev, "fifo");
+	if (irq < 0)
+		return irq;
+
+	ret = devm_request_threaded_irq(dev, irq, NULL, pm8916_bms_vm_fifo_update_done_irq,
+					IRQF_ONESHOT, "pm8916_vm_bms", bat);
+	if (ret)
+		return ret;
+
 	platform_set_drvdata(pdev, bat);
 
 	return 0;