Merge branch 'ser_gigaset-platform-device-dealloc'

Paul Bolle says:

====================
ser_gigaset: fix deallocation of platform device structure

Sascha Levin reported that the syzkaller fuzzer triggered a WARNING in
ser_gigaset (see https://lkml.kernel.org/g/56587467.8050102@oracle.com ). It
turned out that ser_gigaset has always deallocated its platform device
structure incorrectly. Tilman submitted the patch that fixes that (3/4) and a
related cleanup (4/4).

Tilman also submitted a minor cleanup of some NULL checks (1/4) that prompted
Alan to turn those checks into WARN_ONs (2/4). If no one hits these WARN_ONs in
the next couple of releases these WARN_ONs should be removed.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/isdn/gigaset/ser-gigaset.c

@@ -67,8 +67,7 @@ static int write_modem(struct cardstate *cs)
 	struct sk_buff *skb = bcs->tx_skb;
 	int sent = -EOPNOTSUPP;
 
-	if (!tty || !tty->driver || !skb)
-		return -EINVAL;
+	WARN_ON(!tty || !tty->ops || !skb);
 
 	if (!skb->len) {
 		dev_kfree_skb_any(skb);
@@ -109,8 +108,7 @@ static int send_cb(struct cardstate *cs)
 	unsigned long flags;
 	int sent = 0;
 
-	if (!tty || !tty->driver)
-		return -EFAULT;
+	WARN_ON(!tty || !tty->ops);
 
 	cb = cs->cmdbuf;
 	if (!cb)
@@ -370,19 +368,18 @@ static void gigaset_freecshw(struct cardstate *cs)
 	tasklet_kill(&cs->write_tasklet);
 	if (!cs->hw.ser)
 		return;
-	dev_set_drvdata(&cs->hw.ser->dev.dev, NULL);
 	platform_device_unregister(&cs->hw.ser->dev);
-	kfree(cs->hw.ser);
-	cs->hw.ser = NULL;
 }
 
 static void gigaset_device_release(struct device *dev)
 {
-	struct platform_device *pdev = to_platform_device(dev);
+	struct cardstate *cs = dev_get_drvdata(dev);
 
-	/* adapted from platform_device_release() in drivers/base/platform.c */
-	kfree(dev->platform_data);
-	kfree(pdev->resource);
+	if (!cs)
+		return;
+	dev_set_drvdata(dev, NULL);
+	kfree(cs->hw.ser);
+	cs->hw.ser = NULL;
 }
 
 /*
@@ -432,7 +429,9 @@ static int gigaset_set_modem_ctrl(struct cardstate *cs, unsigned old_state,
 	struct tty_struct *tty = cs->hw.ser->tty;
 	unsigned int set, clear;
 
-	if (!tty || !tty->driver || !tty->ops->tiocmset)
+	WARN_ON(!tty || !tty->ops);
+	/* tiocmset is an optional tty driver method */
+	if (!tty->ops->tiocmset)
 		return -EINVAL;
 	set = new_state & ~old_state;
 	clear = old_state & ~new_state;