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/compiler.h>
  12 #include <linux/skbuff.h>
  13 #include <linux/spinlock.h>
  14 #include <linux/netfilter_ipv4.h>
  15 #include <net/inet_ecn.h>
  16 #include <net/ip.h>
  17 #include <net/xfrm.h>
  18 #include <net/icmp.h>
  19
  20 /* Add encapsulation header.
  21  *
  22  * In transport mode, the IP header will be moved forward to make space
  23  * for the encapsulation header.
  24  *
  25  * In tunnel mode, the top IP header will be constructed per RFC 2401.
  26  * The following fields in it shall be filled in by x->type->output:
  27  *      tot_len
  28  *      check
  29  *
  30  * On exit, skb->h will be set to the start of the payload to be processed
  31  * by x->type->output and skb->nh will be set to the top IP header.
  32  */
  33 static void xfrm4_encap(struct sk_buff *skb)
  34 {
  35         struct dst_entry *dst = skb->dst;
  36         struct xfrm_state *x = dst->xfrm;
  37         struct iphdr *iph, *top_iph;
  38         int flags;
  39
  40         iph = skb->nh.iph;
  41         skb->h.ipiph = iph;
  42
  43         skb->nh.raw = skb_push(skb, x->props.header_len);
  44         top_iph = skb->nh.iph;
  45
  46         if (!x->props.mode) {
  47                 skb->h.raw += iph->ihl*4;
  48                 memmove(top_iph, iph, iph->ihl*4);
  49                 return;
  50         }
  51
  52         top_iph->ihl = 5;
  53         top_iph->version = 4;
  54
  55         /* DS disclosed */
  56         top_iph->tos = INET_ECN_encapsulate(iph->tos, iph->tos);
  57
  58         flags = x->props.flags;
  59         if (flags & XFRM_STATE_NOECN)
  60                 IP_ECN_clear(top_iph);
  61
  62         top_iph->frag_off = (flags & XFRM_STATE_NOPMTUDISC) ?
  63                 0 : (iph->frag_off & htons(IP_DF));
  64         if (!top_iph->frag_off)
  65                 __ip_select_ident(top_iph, dst->child, 0);
  66
  67         top_iph->ttl = dst_metric(dst->child, RTAX_HOPLIMIT);
  68
  69         top_iph->saddr = x->props.saddr.a4;
  70         top_iph->daddr = x->id.daddr.a4;
  71         top_iph->protocol = IPPROTO_IPIP;
  72
  73         memset(&(IPCB(skb)->opt), 0, sizeof(struct ip_options));
  74 }
  75
  76 static int xfrm4_tunnel_check_size(struct sk_buff *skb)
  77 {
  78         int mtu, ret = 0;
  79         struct dst_entry *dst;
  80         struct iphdr *iph = skb->nh.iph;
  81
  82         if (IPCB(skb)->flags & IPSKB_XFRM_TUNNEL_SIZE)
  83                 goto out;
  84
  85         IPCB(skb)->flags |= IPSKB_XFRM_TUNNEL_SIZE;
  86
  87         if (!(iph->frag_off & htons(IP_DF)) || skb->local_df)
  88                 goto out;
  89
  90         dst = skb->dst;
  91         mtu = dst_mtu(dst);
  92         if (skb->len > mtu) {
  93                 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, htonl(mtu));
  94                 ret = -EMSGSIZE;
  95         }
  96 out:
  97         return ret;
  98 }
  99
 100 static int xfrm4_output_one(struct sk_buff *skb)
 101 {
 102         struct dst_entry *dst = skb->dst;
 103         struct xfrm_state *x = dst->xfrm;
 104         int err;
 105
 106         if (skb->ip_summed == CHECKSUM_HW) {
 107                 err = skb_checksum_help(skb, 0);
 108                 if (err)
 109                         goto error_nolock;
 110         }
 111
 112         if (x->props.mode) {
 113                 err = xfrm4_tunnel_check_size(skb);
 114                 if (err)
 115                         goto error_nolock;
 116         }
 117
 118         do {
 119                 spin_lock_bh(&x->lock);
 120                 err = xfrm_state_check(x, skb);
 121                 if (err)
 122                         goto error;
 123
 124                 xfrm4_encap(skb);
 125
 126                 err = x->type->output(x, skb);
 127                 if (err)
 128                         goto error;
 129
 130                 x->curlft.bytes += skb->len;
 131                 x->curlft.packets++;
 132
 133                 spin_unlock_bh(&x->lock);
 134
 135                 if (!(skb->dst = dst_pop(dst))) {
 136                         err = -EHOSTUNREACH;
 137                         goto error_nolock;
 138                 }
 139                 dst = skb->dst;
 140                 x = dst->xfrm;
 141         } while (x && !x->props.mode);
 142
 143         IPCB(skb)->flags |= IPSKB_XFRM_TRANSFORMED;
 144         err = 0;
 145
 146 out_exit:
 147         return err;
 148 error:
 149         spin_unlock_bh(&x->lock);
 150 error_nolock:
 151         kfree_skb(skb);
 152         goto out_exit;
 153 }
 154
 155 static int xfrm4_output_finish(struct sk_buff *skb)
 156 {
 157         int err;
 158
 159 #ifdef CONFIG_NETFILTER
 160         if (!skb->dst->xfrm) {
 161                 IPCB(skb)->flags |= IPSKB_REROUTED;
 162                 return dst_output(skb);
 163         }
 164 #endif
 165         while (likely((err = xfrm4_output_one(skb)) == 0)) {
 166                 nf_reset(skb);
 167
 168                 err = nf_hook(PF_INET, NF_IP_LOCAL_OUT, &skb, NULL,
 169                               skb->dst->dev, dst_output);
 170                 if (unlikely(err != 1))
 171                         break;
 172
 173                 if (!skb->dst->xfrm)
 174                         return dst_output(skb);
 175
 176                 err = nf_hook(PF_INET, NF_IP_POST_ROUTING, &skb, NULL,
 177                               skb->dst->dev, xfrm4_output_finish);
 178                 if (unlikely(err != 1))
 179                         break;
 180         }
 181
 182         return err;
 183 }
 184
 185 int xfrm4_output(struct sk_buff *skb)
 186 {
 187         return NF_HOOK_COND(PF_INET, NF_IP_POST_ROUTING, skb, NULL, skb->dst->dev,
 188                             xfrm4_output_finish,
 189                             !(IPCB(skb)->flags & IPSKB_REROUTED));
 190 }