net/ipv4/xfrm4_mode_transport.c

   1 /*
   2  * xfrm4_mode_transport.c - Transport mode encapsulation for IPv4.
   3  *
   4  * Copyright (c) 2004-2006 Herbert Xu <herbert@gondor.apana.org.au>
   5  */
   6
   7 #include <linux/init.h>
   8 #include <linux/kernel.h>
   9 #include <linux/module.h>
  10 #include <linux/skbuff.h>
  11 #include <linux/stringify.h>
  12 #include <net/dst.h>
  13 #include <net/ip.h>
  14 #include <net/xfrm.h>
  15
  16 /* Add encapsulation header.
  17  *
  18  * The IP header will be moved forward to make space for the encapsulation
  19  * header.
  20  */
  21 static int xfrm4_transport_output(struct xfrm_state *x, struct sk_buff *skb)
  22 {
  23         struct iphdr *iph = ip_hdr(skb);
  24         int ihl = iph->ihl * 4;
  25
  26         skb_set_network_header(skb, -x->props.header_len);
  27         skb->mac_header = skb->network_header +
  28                           offsetof(struct iphdr, protocol);
  29         skb->transport_header = skb->network_header + ihl;
  30         __skb_pull(skb, ihl);
  31         memmove(skb_network_header(skb), iph, ihl);
  32         return 0;
  33 }
  34
  35 /* Remove encapsulation header.
  36  *
  37  * The IP header will be moved over the top of the encapsulation header.
  38  *
  39  * On entry, skb->h shall point to where the IP header should be and skb->nh
  40  * shall be set to where the IP header currently is.  skb->data shall point
  41  * to the start of the payload.
  42  */
  43 static int xfrm4_transport_input(struct xfrm_state *x, struct sk_buff *skb)
  44 {
  45         int ihl = skb->data - skb_transport_header(skb);
  46
  47         if (skb->transport_header != skb->network_header) {
  48                 memmove(skb_transport_header(skb),
  49                         skb_network_header(skb), ihl);
  50                 skb->network_header = skb->transport_header;
  51         }
  52         ip_hdr(skb)->tot_len = htons(skb->len + ihl);
  53         skb_reset_transport_header(skb);
  54         return 0;
  55 }
  56
  57 static struct xfrm_mode xfrm4_transport_mode = {
  58         .input = xfrm4_transport_input,
  59         .output = xfrm4_transport_output,
  60         .owner = THIS_MODULE,
  61         .encap = XFRM_MODE_TRANSPORT,
  62 };
  63
  64 static int __init xfrm4_transport_init(void)
  65 {
  66         return xfrm_register_mode(&xfrm4_transport_mode, AF_INET);
  67 }
  68
  69 static void __exit xfrm4_transport_exit(void)
  70 {
  71         int err;
  72
  73         err = xfrm_unregister_mode(&xfrm4_transport_mode, AF_INET);
  74         BUG_ON(err);
  75 }
  76
  77 module_init(xfrm4_transport_init);
  78 module_exit(xfrm4_transport_exit);
  79 MODULE_LICENSE("GPL");
  80 MODULE_ALIAS_XFRM_MODE(AF_INET, XFRM_MODE_TRANSPORT);