audit: eliminate unnecessary extra layer of watch parent references

The audit watch parent count was imbalanced, adding an unnecessary layer of
watch parent references.  Decrement the additional parent reference when a
watch is reused, already having a reference to the parent.

audit_find_parent() gets a reference to the parent, if the parent is
already known.  This additional parental reference is not needed if the
watch is subsequently found by audit_add_to_parent(), and consumed if
the watch does not already exist, so we need to put the parent if the
watch is found, and do nothing if this new watch is added to the parent.

If the parent wasn't already known, it is created with a refcount of 1
and added to the audit_watch_group, then incremented by one to be
subsequently consumed by the newly created watch in
audit_add_to_parent().

The rule points to the watch, not to the parent, so the rule's refcount
gets bumped, not the parent's.

See LKML, 2015-07-16

Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Paul Moore <pmoore@redhat.com>

kernel/audit_watch.c

@@ -391,11 +391,12 @@ static void audit_add_to_parent(struct audit_krule *krule,
 
 		audit_get_watch(w);
 		krule->watch = watch = w;
+
+		audit_put_parent(parent);
 		break;
 	}
 
 	if (!watch_found) {
-		audit_get_parent(parent);
 		watch->parent = parent;
 
 		audit_get_watch(watch);
@@ -436,9 +437,6 @@ int audit_add_watch(struct audit_krule *krule, struct list_head **list)
 
 	audit_add_to_parent(krule, parent);
 
-	/* match get in audit_find_parent or audit_init_parent */
-	audit_put_parent(parent);
-
 	h = audit_hash_ino((u32)watch->ino);
 	*list = &audit_inode_hash[h];
 error: