xfrm: extend MIGRATE with UDP encapsulation port

Add UDP encapsulation port to XFRM_MSG_MIGRATE using an optional
netlink attribute XFRMA_ENCAP.

The devices that support IKE MOBIKE extension (RFC-4555 Section 3.8)
could go to sleep for a few minutes and wake up. When it wake up the
NAT mapping could have expired, the device send a MOBIKE UPDATE_SA
message to migrate the IPsec SA. The change could be a change UDP
encapsulation port, IP address, or both.

Reported-by: Paul Wouters <pwouters@redhat.com>
Signed-off-by: Antony Antony <antony@phenome.org>
Reviewed-by: Richard Guy Briggs <rgb@tricolour.ca>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index 38614df..fb98892 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -2243,6 +2243,7 @@ static int xfrm_do_migrate(struct sk_buff *skb, struct nlmsghdr *nlh,
 	int err;
 	int n = 0;
 	struct net *net = sock_net(skb->sk);
+	struct xfrm_encap_tmpl  *encap = NULL;
 
 	if (attrs[XFRMA_MIGRATE] == NULL)
 		return -EINVAL;
@@ -2260,9 +2261,18 @@ static int xfrm_do_migrate(struct sk_buff *skb, struct nlmsghdr *nlh,
 	if (!n)
 		return 0;
 
-	xfrm_migrate(&pi->sel, pi->dir, type, m, n, kmp, net);
+	if (attrs[XFRMA_ENCAP]) {
+		encap = kmemdup(nla_data(attrs[XFRMA_ENCAP]),
+				sizeof(*encap), GFP_KERNEL);
+		if (!encap)
+			return 0;
+	}
 
-	return 0;
+	err = xfrm_migrate(&pi->sel, pi->dir, type, m, n, kmp, net, encap);
+
+	kfree(encap);
+
+	return err;
 }
 #else
 static int xfrm_do_migrate(struct sk_buff *skb, struct nlmsghdr *nlh,