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: NNick Dyer <nick.dyer@itdev.co.uk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/sysfs/file.c

@@ -449,11 +449,13 @@ void sysfs_notify_dirent(struct sysfs_dirent *sd)
 
 	spin_lock_irqsave(&sysfs_open_dirent_lock, flags);
 
+	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);
 }