netdev - [PATCH net-next v2 3/5] mpls: Differentiate implicit-null and unlabeled neighbours

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Date:	Fri, 20 Mar 2015 15:42:48 +0000
From:	Robert Shearman <rshearma@...cade.com>
To:	<davem@...emloft.net>
CC:	<netdev@...r.kernel.org>, Robert Shearman <rshearma@...cade.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH net-next v2 3/5] mpls: Differentiate implicit-null and unlabeled neighbours

The control plane can advertise labels for neighbours that don't have
an outgoing label. RFC 3032 s3.22 states that either the remaining
labels should be popped (if the control plane can determine that it's
safe to do so, which in light of MPLS-VPN, RFC 4364, is never the case
now) or that the packet should be discarded.

Therefore, if the peer is unlabeled and the last label wasn't popped
then drop the packet. The peer being unlabeled is signalled by an
empty label stack. However, implicit-null still needs to be supported
(i.e. penultimate hop popping) where the incoming label is popped and
no labels are put on and the packet can still go out labeled with the
unpopped part of the stack. This is achieved by the control plane
specifying a label stack consisting of the single special
implicit-null value.

Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
Signed-off-by: Robert Shearman <rshearma@...cade.com>
---
 net/mpls/af_mpls.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/net/mpls/af_mpls.c b/net/mpls/af_mpls.c
index bf3459a..e3586a7 100644
--- a/net/mpls/af_mpls.c
+++ b/net/mpls/af_mpls.c
@@ -28,7 +28,8 @@ struct mpls_route { /* next hop label forwarding entry */
 	struct rcu_head		rt_rcu;
 	u32			rt_label[MAX_NEW_LABELS];
 	u8			rt_protocol; /* routing protocol that set this entry */
-	u8			rt_labels;
+	u8                      rt_unlabeled : 1;
+	u8			rt_labels : 7;
 	u8			rt_via_alen;
 	u8			rt_via_table;
 	u8			rt_via[0];
@@ -201,6 +202,11 @@ static int mpls_forward(struct sk_buff *skb, struct net_device *dev,
 	if (unlikely(!new_header_size && dec.bos)) {
 		if (!mpls_egress(rt, skb, dec))
 			goto drop;
+	} else if (rt->rt_unlabeled) {
+		/* Labeled traffic destined to unlabeled peer should
+		 * be discarded
+		 */
+		goto drop;
 	} else {
 		bool bos;
 		int i;
@@ -385,9 +391,16 @@ static int mpls_route_add(struct mpls_route_config *cfg)
 	if (!rt)
 		goto errout;
 
-	rt->rt_labels = cfg->rc_output_labels;
-	for (i = 0; i < rt->rt_labels; i++)
-		rt->rt_label[i] = cfg->rc_output_label[i];
+	if (cfg->rc_output_labels == 1 &&
+	    cfg->rc_output_label[0] == LABEL_IMPLICIT_NULL) {
+		rt->rt_labels = 0;
+	} else {
+		rt->rt_labels = cfg->rc_output_labels;
+		for (i = 0; i < rt->rt_labels; i++)
+			rt->rt_label[i] = cfg->rc_output_label[i];
+		if (!rt->rt_labels)
+			rt->rt_unlabeled = true;
+	}
 	rt->rt_protocol = cfg->rc_protocol;
 	RCU_INIT_POINTER(rt->rt_dev, dev);
 	rt->rt_via_table = cfg->rc_via_table;
-- 
2.1.4

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