UBUNTU: SAUCE: apparmor: fix label leak when new label is unused

When a new label is created, it is created with a proxy in a circular
ref count that is broken by replacement. However if the label is not
used it will never be replaced and the circular ref count will never
be broken resulting in a leak.

BugLink: http://bugs.launchpad.net/bugs/1660834Signed-off-by: John Johansen <john.johansen@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Tim Gardner <tim.gardner@canonical.com>
Acked-by: Brad Figg <brad.figg@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

security/apparmor/label.c

@@ -308,6 +308,8 @@ int aa_vec_unique(struct aa_profile **vec, int n, int flags)
 
 static void label_destroy(struct aa_label *label)
 {
+	struct aa_label *tmp;
+
 	AA_BUG(!label);
 
 	if (label_is_stale(label))
@@ -329,6 +331,11 @@ static void label_destroy(struct aa_label *label)
 		rcu_assign_pointer(label->proxy->label, NULL);
 
 	aa_free_sid(label->sid);
+
+	tmp = rcu_dereference_protected(label->proxy->label, true);
+	if (tmp == label)
+		rcu_assign_pointer(label->proxy->label, NULL);
+
 	aa_put_proxy(label->proxy);
 	label->proxy = (struct aa_proxy *) PROXY_POISON + 1;
 }
@@ -380,6 +387,15 @@ void aa_label_kref(struct kref *kref)
 	call_rcu(&label->rcu, label_free_rcu);
 }
 
+static void label_free_or_put_new(struct aa_label *label, struct aa_label *new)
+{
+	if (label != new)
+		/* need to free directly to break circular ref with proxy */
+		aa_label_free(new);
+	else
+		aa_put_label(new);
+}
+
 bool aa_label_init(struct aa_label *label, int size)
 {
 	AA_BUG(!label);
@@ -842,7 +858,7 @@ static struct aa_label *vec_create_and_insert_label(struct aa_profile **vec,
 	write_lock_irqsave(&ls->lock, flags);
 	label = __label_insert(ls, new, false);
 	write_unlock_irqrestore(&ls->lock, flags);
-	aa_put_label(new);
+	label_free_or_put_new(label, new);
 
 	return label;
 }
@@ -1241,7 +1257,7 @@ struct aa_label *aa_label_merge(struct aa_label *a, struct aa_label *b,
 			goto out;
 
 		label = label_merge_insert(new, a, b);
-		aa_put_label(new);
+		label_free_or_put_new(label, new);
 	out:
 		aa_put_label(a);
 		aa_put_label(b);
@@ -2042,8 +2058,7 @@ static struct aa_label *__label_update(struct aa_label *label)
 	/* ensure label is removed, and redirected correctly */
 	__label_remove(label, tmp);
 	write_unlock_irqrestore(&ls->lock, flags);
-
-	aa_put_label(new);
+	label_free_or_put_new(tmp, new);
 
 	return tmp;
 }