[IPSEC] xfrm: Abstract out encapsulation modes

This patch adds the structure xfrm_mode.  It is meant to represent
the operations carried out by transport/tunnel modes.

By doing this we allow additional encapsulation modes to be added
without clogging up the xfrm_input/xfrm_output paths.

Candidate modes include 4-to-6 tunnel mode, 6-to-4 tunnel mode, and
BEET modes.

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

1 files changed, 125 insertions, 0 deletions

diff --git a/net/ipv4/xfrm4_mode_tunnel.c b/net/ipv4/xfrm4_mode_tunnel.c
new file mode 100644
index 00000000000..f8d880beb12
--- /dev/null
+++ b/net/ipv4/xfrm4_mode_tunnel.c
@@ -0,0 +1,125 @@
+/*
+ * xfrm4_mode_tunnel.c - Tunnel mode encapsulation for IPv4.
+ *
+ * Copyright (c) 2004-2006 Herbert Xu <herbert@gondor.apana.org.au>
+ */
+
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/stringify.h>
+#include <net/dst.h>
+#include <net/inet_ecn.h>
+#include <net/ip.h>
+#include <net/xfrm.h>
+
+static inline void ipip_ecn_decapsulate(struct sk_buff *skb)
+{
+	struct iphdr *outer_iph = skb->nh.iph;
+	struct iphdr *inner_iph = skb->h.ipiph;
+
+	if (INET_ECN_is_ce(outer_iph->tos))
+		IP_ECN_set_ce(inner_iph);
+}
+
+/* Add encapsulation header.
+ *
+ * The top IP header will be constructed per RFC 2401.  The following fields
+ * in it shall be filled in by x->type->output:
+ *      tot_len
+ *      check
+ *
+ * On exit, skb->h will be set to the start of the payload to be processed
+ * by x->type->output and skb->nh will be set to the top IP header.
+ */
+static int xfrm4_tunnel_output(struct sk_buff *skb)
+{
+	struct dst_entry *dst = skb->dst;
+	struct xfrm_state *x = dst->xfrm;
+	struct iphdr *iph, *top_iph;
+	int flags;
+
+	iph = skb->nh.iph;
+	skb->h.ipiph = iph;
+
+	skb->nh.raw = skb_push(skb, x->props.header_len);
+	top_iph = skb->nh.iph;
+
+	top_iph->ihl = 5;
+	top_iph->version = 4;
+
+	/* DS disclosed */
+	top_iph->tos = INET_ECN_encapsulate(iph->tos, iph->tos);
+
+	flags = x->props.flags;
+	if (flags & XFRM_STATE_NOECN)
+		IP_ECN_clear(top_iph);
+
+	top_iph->frag_off = (flags & XFRM_STATE_NOPMTUDISC) ?
+		0 : (iph->frag_off & htons(IP_DF));
+	if (!top_iph->frag_off)
+		__ip_select_ident(top_iph, dst->child, 0);
+
+	top_iph->ttl = dst_metric(dst->child, RTAX_HOPLIMIT);
+
+	top_iph->saddr = x->props.saddr.a4;
+	top_iph->daddr = x->id.daddr.a4;
+	top_iph->protocol = IPPROTO_IPIP;
+
+	memset(&(IPCB(skb)->opt), 0, sizeof(struct ip_options));
+	return 0;
+}
+
+static int xfrm4_tunnel_input(struct xfrm_state *x, struct sk_buff *skb)
+{
+	struct iphdr *iph = skb->nh.iph;
+	int err = -EINVAL;
+
+	if (iph->protocol != IPPROTO_IPIP)
+		goto out;
+	if (!pskb_may_pull(skb, sizeof(struct iphdr)))
+		goto out;
+
+	if (skb_cloned(skb) &&
+	    (err = pskb_expand_head(skb, 0, 0, GFP_ATOMIC)))
+		goto out;
+
+	if (x->props.flags & XFRM_STATE_DECAP_DSCP)
+		ipv4_copy_dscp(iph, skb->h.ipiph);
+	if (!(x->props.flags & XFRM_STATE_NOECN))
+		ipip_ecn_decapsulate(skb);
+	skb->mac.raw = memmove(skb->data - skb->mac_len,
+			       skb->mac.raw, skb->mac_len);
+	skb->nh.raw = skb->data;
+	memset(&(IPCB(skb)->opt), 0, sizeof(struct ip_options));
+	err = 0;
+
+out:
+	return err;
+}
+
+static struct xfrm_mode xfrm4_tunnel_mode = {
+	.input = xfrm4_tunnel_input,
+	.output = xfrm4_tunnel_output,
+	.owner = THIS_MODULE,
+	.encap = XFRM_MODE_TUNNEL,
+};
+
+static int __init xfrm4_tunnel_init(void)
+{
+	return xfrm_register_mode(&xfrm4_tunnel_mode, AF_INET);
+}
+
+static void __exit xfrm4_tunnel_exit(void)
+{
+	int err;
+
+	err = xfrm_unregister_mode(&xfrm4_tunnel_mode, AF_INET);
+	BUG_ON(err);
+}
+
+module_init(xfrm4_tunnel_init);
+module_exit(xfrm4_tunnel_exit);
+MODULE_LICENSE("GPL");
+MODULE_ALIAS_XFRM_MODE(AF_INET, XFRM_MODE_TUNNEL);