+/* If it's a keepalive packet, then just eat it.
+ * If it's an encapsulated packet, then pass it to the
+ * IPsec xfrm input.
+ * Returns 0 if skb passed to xfrm or was dropped.
+ * Returns >0 if skb should be passed to UDP.
+ * Returns <0 if skb should be resubmitted (-ret is protocol)
+ */
+int xfrm4_udp_encap_rcv(struct sock *sk, struct sk_buff *skb)
+{
+ struct udp_sock *up = udp_sk(sk);
+ struct udphdr *uh;
+ struct iphdr *iph;
+ int iphlen, len;
+ int ret;
+
+ __u8 *udpdata;
+ __be32 *udpdata32;
+ __u16 encap_type = up->encap_type;
+
+ /* if this is not encapsulated socket, then just return now */
+ if (!encap_type)
+ return 1;
+
+ /* If this is a paged skb, make sure we pull up
+ * whatever data we need to look at. */
+ len = skb->len - sizeof(struct udphdr);
+ if (!pskb_may_pull(skb, sizeof(struct udphdr) + min(len, 8)))
+ return 1;
+
+ /* Now we can get the pointers */
+ uh = udp_hdr(skb);
+ udpdata = (__u8 *)uh + sizeof(struct udphdr);
+ udpdata32 = (__be32 *)udpdata;
+
+ switch (encap_type) {
+ default:
+ case UDP_ENCAP_ESPINUDP:
+ /* Check if this is a keepalive packet. If so, eat it. */
+ if (len == 1 && udpdata[0] == 0xff) {