[IPSEC] proto: Move transport mode input path into xfrm_mode_transport

Now that we have xfrm_mode objects we can move the transport mode specific
input decapsulation code into xfrm_mode_transport.  This removes duplicate
code as well as unnecessary header movement in case of tunnel mode SAs
since we will discard the original IP header immediately.

This also fixes a minor bug for transport-mode ESP where the IP payload
length is set to the correct value minus the header length (with extension
headers for IPv6).

Of course the other neat thing is that we no longer have to allocate
temporary buffers to hold the IP headers for ESP and IPComp.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 14 insertions, 0 deletions

diff --git a/net/ipv4/xfrm4_mode_transport.c b/net/ipv4/xfrm4_mode_transport.c
index e46d9a4ccc55..a9e6b3dd19c9 100644
--- a/net/ipv4/xfrm4_mode_transport.c
+++ b/net/ipv4/xfrm4_mode_transport.c
@@ -38,8 +38,22 @@ static int xfrm4_transport_output(struct sk_buff *skb)
 	return 0;
 }
 
+/* Remove encapsulation header.
+ *
+ * The IP header will be moved over the top of the encapsulation header.
+ *
+ * On entry, skb->h shall point to where the IP header should be and skb->nh
+ * shall be set to where the IP header currently is.  skb->data shall point
+ * to the start of the payload.
+ */
 static int xfrm4_transport_input(struct xfrm_state *x, struct sk_buff *skb)
 {
+	int ihl = skb->data - skb->h.raw;
+
+	if (skb->h.raw != skb->nh.raw)
+		skb->nh.raw = memmove(skb->h.raw, skb->nh.raw, ihl);
+	skb->nh.iph->tot_len = htons(skb->len + ihl);
+	skb->h.raw = skb->data;
 	return 0;
 }