net/ipv4/xfrm4_output.c

   1 /*
   2  * xfrm4_output.c - Common IPsec encapsulation code for IPv4.
   3  * Copyright (c) 2004 Herbert Xu <herbert@gondor.apana.org.au>
   4  *
   5  * This program is free software; you can redistribute it and/or
   6  * modify it under the terms of the GNU General Public License
   7  * as published by the Free Software Foundation; either version
   8  * 2 of the License, or (at your option) any later version.
   9  */
  10
  11 #include <linux/skbuff.h>
  12 #include <linux/spinlock.h>
  13 #include <net/inet_ecn.h>
  14 #include <net/ip.h>
  15 #include <net/xfrm.h>
  16 #include <net/icmp.h>
  17
  18 /* Add encapsulation header.
  19  *
  20  * In transport mode, the IP header will be moved forward to make space
  21  * for the encapsulation header.
  22  *
  23  * In tunnel mode, the top IP header will be constructed per RFC 2401.
  24  * The following fields in it shall be filled in by x->type->output:
  25  *      tot_len
  26  *      check
  27  *
  28  * On exit, skb->h will be set to the start of the payload to be processed
  29  * by x->type->output and skb->nh will be set to the top IP header.
  30  */
  31 static void xfrm4_encap(struct sk_buff *skb)
  32 {
  33         struct dst_entry *dst = skb->dst;
  34         struct xfrm_state *x = dst->xfrm;
  35         struct iphdr *iph, *top_iph;
  36
  37         iph = skb->nh.iph;
  38         skb->h.ipiph = iph;
  39
  40         skb->nh.raw = skb_push(skb, x->props.header_len);
  41         top_iph = skb->nh.iph;
  42
  43         if (!x->props.mode) {
  44                 skb->h.raw += iph->ihl*4;
  45                 memmove(top_iph, iph, iph->ihl*4);
  46                 return;
  47         }
  48
  49         top_iph->ihl = 5;
  50         top_iph->version = 4;
  51
  52         /* DS disclosed */
  53         top_iph->tos = INET_ECN_encapsulate(iph->tos, iph->tos);
  54         if (x->props.flags & XFRM_STATE_NOECN)
  55                 IP_ECN_clear(top_iph);
  56
  57         top_iph->frag_off = iph->frag_off & htons(IP_DF);
  58         if (!top_iph->frag_off)
  59                 __ip_select_ident(top_iph, dst, 0);
  60
  61         top_iph->ttl = dst_metric(dst->child, RTAX_HOPLIMIT);
  62
  63         top_iph->saddr = x->props.saddr.a4;
  64         top_iph->daddr = x->id.daddr.a4;
  65         top_iph->protocol = IPPROTO_IPIP;
  66
  67         memset(&(IPCB(skb)->opt), 0, sizeof(struct ip_options));
  68 }
  69
  70 static int xfrm4_tunnel_check_size(struct sk_buff *skb)
  71 {
  72         int mtu, ret = 0;
  73         struct dst_entry *dst;
  74         struct iphdr *iph = skb->nh.iph;
  75
  76         if (IPCB(skb)->flags & IPSKB_XFRM_TUNNEL_SIZE)
  77                 goto out;
  78
  79         IPCB(skb)->flags |= IPSKB_XFRM_TUNNEL_SIZE;
  80
  81         if (!(iph->frag_off & htons(IP_DF)) || skb->local_df)
  82                 goto out;
  83
  84         dst = skb->dst;
  85         mtu = dst_mtu(dst);
  86         if (skb->len > mtu) {
  87                 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, htonl(mtu));
  88                 ret = -EMSGSIZE;
  89         }
  90 out:
  91         return ret;
  92 }
  93
  94 int xfrm4_output(struct sk_buff *skb)
  95 {
  96         struct dst_entry *dst = skb->dst;
  97         struct xfrm_state *x = dst->xfrm;
  98         int err;
  99
 100         if (skb->ip_summed == CHECKSUM_HW) {
 101                 err = skb_checksum_help(skb, 0);
 102                 if (err)
 103                         goto error_nolock;
 104         }
 105
 106         if (x->props.mode) {
 107                 err = xfrm4_tunnel_check_size(skb);
 108                 if (err)
 109                         goto error_nolock;
 110         }
 111
 112         spin_lock_bh(&x->lock);
 113         err = xfrm_state_check(x, skb);
 114         if (err)
 115                 goto error;
 116
 117         xfrm4_encap(skb);
 118
 119         err = x->type->output(x, skb);
 120         if (err)
 121                 goto error;
 122
 123         x->curlft.bytes += skb->len;
 124         x->curlft.packets++;
 125
 126         spin_unlock_bh(&x->lock);
 127
 128         if (!(skb->dst = dst_pop(dst))) {
 129                 err = -EHOSTUNREACH;
 130                 goto error_nolock;
 131         }
 132         err = NET_XMIT_BYPASS;
 133
 134 out_exit:
 135         return err;
 136 error:
 137         spin_unlock_bh(&x->lock);
 138 error_nolock:
 139         kfree_skb(skb);
 140         goto out_exit;
 141 }