[PATCH 2/2] ser_gigaset: use container_of() instead of detour

[Paul Bolle]

The purpose of gigaset_device_release() is to kfree() the struct
ser_cardstate that contains our struct device. This is done via a bit of
a detour. First we make our struct device's driver_data point to the
container of our struct ser_cardstate (which is a struct cardstate). In
gigaset_device_release() we then retrieve that driver_data again. And
after that we finally kfree() the struct ser_cardstate that was saved in
the struct cardstate.

All of this can be achieved much easier by using container_of() to get
from our struct device to its container, struct ser_cardstate. Do so.

Note that the detour via driver_data broke down in commit 25cad69f21f5
("base/platform: Fix platform drivers with no probe callback"). That
commit reconnected our platform_device and our platform_driver again.
And one of the consequences of that fix was that
__device_release_driver() no longer is a NOP for our struct device but
actually does stuff again. One of the things it does, is setting our
driver_data to NULL. That, in turn, makes it impossible for
gigaset_device_release() to get to our struct cardstate. Which has the
net effect of leaking a struct ser_cardstate at every call of this
driver's tty close() operation. So using container_of() has the
additional benefit of actually working.

Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Not-yet-signed-off-by: Paul Bolle <pebolle@xxxxxxxxxx>
---
 drivers/isdn/gigaset/ser-gigaset.c | 9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/drivers/isdn/gigaset/ser-gigaset.c b/drivers/isdn/gigaset/ser-gigaset.c
index ae69ab89c5c0..6d40800f362c 100644
--- a/drivers/isdn/gigaset/ser-gigaset.c
+++ b/drivers/isdn/gigaset/ser-gigaset.c
@@ -373,13 +373,7 @@ static void gigaset_freecshw(struct cardstate *cs)
 
 static void gigaset_device_release(struct device *dev)
 {
-	struct cardstate *cs = dev_get_drvdata(dev);
-
-	if (!cs)
-		return;
-	dev_set_drvdata(dev, NULL);
-	kfree(cs->hw.ser);
-	cs->hw.ser = NULL;
+	kfree(container_of(dev, struct ser_cardstate, dev.dev));
 }
 
 /*
@@ -408,7 +402,6 @@ static int gigaset_initcshw(struct cardstate *cs)
 		cs->hw.ser = NULL;
 		return rc;
 	}
-	dev_set_drvdata(&cs->hw.ser->dev.dev, cs);
 
 	tasklet_init(&cs->write_tasklet,
 		     gigaset_modem_fill, (unsigned long) cs);
-- 
2.4.3