net: mpls: Pull common label check into helper

BugLink: http://bugs.launchpad.net/bugs/1764367

commit b7b386f4 upstream.

mpls_route_add and mpls_route_del have the same checks on the label.
Move to a helper. Avoid duplicate extack messages in the next patch.
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

net/mpls/af_mpls.c

@@ -716,6 +716,19 @@ static int mpls_nh_build_multi(struct mpls_route_config *cfg,
 	return err;
 }
 
+static bool mpls_label_ok(struct net *net, unsigned int index)
+{
+	/* Reserved labels may not be set */
+	if (index < MPLS_LABEL_FIRST_UNRESERVED)
+		return false;
+
+	/* The full 20 bit range may not be supported. */
+	if (index >= net->mpls.platform_labels)
+		return false;
+
+	return true;
+}
+
 static int mpls_route_add(struct mpls_route_config *cfg)
 {
 	struct mpls_route __rcu **platform_label;
@@ -734,12 +747,7 @@ static int mpls_route_add(struct mpls_route_config *cfg)
 		index = find_free_label(net);
 	}
 
-	/* Reserved labels may not be set */
-	if (index < MPLS_LABEL_FIRST_UNRESERVED)
-		goto errout;
-
-	/* The full 20 bit range may not be supported. */
-	if (index >= net->mpls.platform_labels)
+	if (!mpls_label_ok(net, index))
 		goto errout;
 
 	/* Append makes no sense with mpls */
@@ -800,12 +808,7 @@ static int mpls_route_del(struct mpls_route_config *cfg)
 
 	index = cfg->rc_label;
 
-	/* Reserved labels may not be removed */
-	if (index < MPLS_LABEL_FIRST_UNRESERVED)
-		goto errout;
-
-	/* The full 20 bit range may not be supported */
-	if (index >= net->mpls.platform_labels)
+	if (!mpls_label_ok(net, index))
 		goto errout;
 
 	mpls_route_update(net, index, NULL, &cfg->rc_nlinfo);
@@ -1164,10 +1167,9 @@ static int rtm_to_route_config(struct sk_buff *skb,  struct nlmsghdr *nlh,
 					   &cfg->rc_label))
 				goto errout;
 
-			/* Reserved labels may not be set */
-			if (cfg->rc_label < MPLS_LABEL_FIRST_UNRESERVED)
+			if (!mpls_label_ok(cfg->rc_nlinfo.nl_net,
+					   cfg->rc_label))
 				goto errout;
-
 			break;
 		}
 		case RTA_VIA: