sysfs_notify is only possible on file attributes

If sysfs_notify is called on a binary attribute, bad things can
happen, so prevent it.

Note, no in-kernel usage of this is currently present, but in the
future, it's good to be safe.

Changes in V2:
- Also ignore sysfs_notify on dirs, links
- Use WARN_ON rather than silently failing
- Compiled and tested (huge apologies about first submission)
Signed-off-by: Nick Dyer <nick.dyer@itdev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/sysfs/file.c

@@ -449,10 +449,12 @@ void sysfs_notify_dirent(struct sysfs_dirent *sd)
 
 	spin_lock_irqsave(&sysfs_open_dirent_lock, flags);
 
-	od = sd->s_attr.open;
-	if (od) {
-		atomic_inc(&od->event);
-		wake_up_interruptible(&od->poll);
+	if (!WARN_ON(sysfs_type(sd) != SYSFS_KOBJ_ATTR)) {
+		od = sd->s_attr.open;
+		if (od) {
+			atomic_inc(&od->event);
+			wake_up_interruptible(&od->poll);
+		}
 	}
 
 	spin_unlock_irqrestore(&sysfs_open_dirent_lock, flags);