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         int flags;
  37
  38         iph = skb->nh.iph;
  39         skb->h.ipiph = iph;
  40
  41         skb->nh.raw = skb_push(skb, x->props.header_len);
  42         top_iph = skb->nh.iph;
  43
  44         if (!x->props.mode) {
  45                 skb->h.raw += iph->ihl*4;
  46                 memmove(top_iph, iph, iph->ihl*4);
  47                 return;
  48         }
  49
  50         top_iph->ihl = 5;
  51         top_iph->version = 4;
  52
  53         /* DS disclosed */
  54         top_iph->tos = INET_ECN_encapsulate(iph->tos, iph->tos);
  55
  56         flags = x->props.flags;
  57         if (flags & XFRM_STATE_NOECN)
  58                 IP_ECN_clear(top_iph);
  59
  60         top_iph->frag_off = (flags & XFRM_STATE_NOPMTUDISC) ?
  61                 0 : (iph->frag_off & htons(IP_DF));
  62         if (!top_iph->frag_off)
  63                 __ip_select_ident(top_iph, dst, 0);
  64
  65         top_iph->ttl = dst_metric(dst->child, RTAX_HOPLIMIT);
  66
  67         top_iph->saddr = x->props.saddr.a4;
  68         top_iph->daddr = x->id.daddr.a4;
  69         top_iph->protocol = IPPROTO_IPIP;
  70
  71         memset(&(IPCB(skb)->opt), 0, sizeof(struct ip_options));
  72 }
  73
  74 static int xfrm4_tunnel_check_size(struct sk_buff *skb)
  75 {
  76         int mtu, ret = 0;
  77         struct dst_entry *dst;
  78         struct iphdr *iph = skb->nh.iph;
  79
  80         if (IPCB(skb)->flags & IPSKB_XFRM_TUNNEL_SIZE)
  81                 goto out;
  82
  83         IPCB(skb)->flags |= IPSKB_XFRM_TUNNEL_SIZE;
  84
  85         if (!(iph->frag_off & htons(IP_DF)) || skb->local_df)
  86                 goto out;
  87
  88         dst = skb->dst;
  89         mtu = dst_mtu(dst);
  90         if (skb->len > mtu) {
  91                 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, htonl(mtu));
  92                 ret = -EMSGSIZE;
  93         }
  94 out:
  95         return ret;
  96 }
  97
  98 int xfrm4_output(struct sk_buff *skb)
  99 {
 100         struct dst_entry *dst = skb->dst;
 101         struct xfrm_state *x = dst->xfrm;
 102         int err;
 103
 104         if (skb->ip_summed == CHECKSUM_HW) {
 105                 err = skb_checksum_help(skb, 0);
 106                 if (err)
 107                         goto error_nolock;
 108         }
 109
 110         if (x->props.mode) {
 111                 err = xfrm4_tunnel_check_size(skb);
 112                 if (err)
 113                         goto error_nolock;
 114         }
 115
 116         spin_lock_bh(&x->lock);
 117         err = xfrm_state_check(x, skb);
 118         if (err)
 119                 goto error;
 120
 121         xfrm4_encap(skb);
 122
 123         err = x->type->output(x, skb);
 124         if (err)
 125                 goto error;
 126
 127         x->curlft.bytes += skb->len;
 128         x->curlft.packets++;
 129
 130         spin_unlock_bh(&x->lock);
 131
 132         if (!(skb->dst = dst_pop(dst))) {
 133                 err = -EHOSTUNREACH;
 134                 goto error_nolock;
 135         }
 136         err = NET_XMIT_BYPASS;
 137
 138 out_exit:
 139         return err;
 140 error:
 141         spin_unlock_bh(&x->lock);
 142 error_nolock:
 143         kfree_skb(skb);
 144         goto out_exit;
 145 }