power: supply: cpcap-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.

Fixes: 874b2adbed12 ("power: supply: cpcap-battery: Add a battery driver")
Signed-off-by: Waqar Hameed <waqar.hameed@axis.com>
Link: https://patch.msgid.link/81db58d610c9a51a68184f856cd431a934cccee2.1766268280.git.waqar.hameed@axis.com
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

diff --git a/drivers/power/supply/cpcap-battery.c b/drivers/power/supply/cpcap-battery.c
index 8106d1edcbc26a738874d16e6bf3ce0547a38143..507fdc1c866d56b32b7d7c5df64ca221a31bbc84 100644 (file)
--- a/drivers/power/supply/cpcap-battery.c
+++ b/drivers/power/supply/cpcap-battery.c
@@ -1122,10 +1122,6 @@ static int cpcap_battery_probe(struct platform_device *pdev)
 
        platform_set_drvdata(pdev, ddata);
 
-       error = cpcap_battery_init_interrupts(pdev, ddata);
-       if (error)
-               return error;
-
        error = cpcap_battery_init_iio(ddata);
        if (error)
                return error;
@@ -1142,6 +1138,10 @@ static int cpcap_battery_probe(struct platform_device *pdev)
                return error;
        }
 
+       error = cpcap_battery_init_interrupts(pdev, ddata);
+       if (error)
+               return error;
+
        atomic_set(&ddata->active, 1);
 
        error = cpcap_battery_calibrate(ddata);