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  * On exit, skb->h will be set to the start of the payload to be processed
  22  * by x->type->output and skb->nh will be set to the top IP header.
  23  */
  24 static int xfrm4_transport_output(struct sk_buff *skb)
  25 {
  26         struct xfrm_state *x;
  27         struct iphdr *iph;
  28         int ihl;
  29
  30         iph = skb->nh.iph;
  31         skb->h.ipiph = iph;
  32
  33         ihl = iph->ihl * 4;
  34         skb->h.raw += ihl;
  35
  36         x = skb->dst->xfrm;
  37         skb->nh.raw = memmove(skb_push(skb, x->props.header_len), iph, ihl);
  38         return 0;
  39 }
  40
  41 /* Remove encapsulation header.
  42  *
  43  * The IP header will be moved over the top of the encapsulation header.
  44  *
  45  * On entry, skb->h shall point to where the IP header should be and skb->nh
  46  * shall be set to where the IP header currently is.  skb->data shall point
  47  * to the start of the payload.
  48  */
  49 static int xfrm4_transport_input(struct xfrm_state *x, struct sk_buff *skb)
  50 {
  51         int ihl = skb->data - skb->h.raw;
  52
  53         if (skb->h.raw != skb->nh.raw)
  54                 skb->nh.raw = memmove(skb->h.raw, skb->nh.raw, ihl);
  55         skb->nh.iph->tot_len = htons(skb->len + ihl);
  56         skb->h.raw = skb->data;
  57         return 0;
  58 }
  59
  60 static struct xfrm_mode xfrm4_transport_mode = {
  61         .input = xfrm4_transport_input,
  62         .output = xfrm4_transport_output,
  63         .owner = THIS_MODULE,
  64         .encap = XFRM_MODE_TRANSPORT,
  65 };
  66
  67 static int __init xfrm4_transport_init(void)
  68 {
  69         return xfrm_register_mode(&xfrm4_transport_mode, AF_INET);
  70 }
  71
  72 static void __exit xfrm4_transport_exit(void)
  73 {
  74         int err;
  75
  76         err = xfrm_unregister_mode(&xfrm4_transport_mode, AF_INET);
  77         BUG_ON(err);
  78 }
  79
  80 module_init(xfrm4_transport_init);
  81 module_exit(xfrm4_transport_exit);
  82 MODULE_LICENSE("GPL");
  83 MODULE_ALIAS_XFRM_MODE(AF_INET, XFRM_MODE_TRANSPORT);