Char/Misc patch for 5.5-rc6

Here is a single fix, for the chrdev core, for 5.5-rc6
 
 There's been a long-standing race condition triggered by syzbot, and
 occasionally real people, in the chrdev open() path.  Will finally took
 the time to track it down and fix it for real before the holidays.
 
 Here's that one patch, it's been in linux-next for a while with no
 reported issues and it does fix the reported problem.
 
 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Merge tag 'char-misc-5.5-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc

Pull char/misc fix from Greg KH:
 "Here is a single fix, for the chrdev core, for 5.5-rc6

  There's been a long-standing race condition triggered by syzbot, and
  occasionally real people, in the chrdev open() path. Will finally took
  the time to track it down and fix it for real before the holidays.

  Here's that one patch, it's been in linux-next for a while with no
  reported issues and it does fix the reported problem"

* tag 'char-misc-5.5-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc:
  chardev: Avoid potential use-after-free in 'chrdev_open()'

fs/char_dev.c

@@ -352,7 +352,7 @@ static struct kobject *cdev_get(struct cdev *p)
 
 	if (owner && !try_module_get(owner))
 		return NULL;
-	kobj = kobject_get(&p->kobj);
+	kobj = kobject_get_unless_zero(&p->kobj);
 	if (!kobj)
 		module_put(owner);
 	return kobj;