net/ipv4/ip_forward.c

   1 /*
   2  * INET         An implementation of the TCP/IP protocol suite for the LINUX
   3  *              operating system.  INET is implemented using the  BSD Socket
   4  *              interface as the means of communication with the user level.
   5  *
   6  *              The IP forwarding functionality.
   7  *
   8  * Version:     $Id: ip_forward.c,v 1.43 1999/03/21 05:22:37 davem Exp $
   9  *
  10  * Authors:     see ip.c
  11  *
  12  * Fixes:
  13  *              Many            :       Split from ip.c , see ip_input.c for
  14  *                                      history.
  15  *              Dave Gregorich  :       NULL ip_rt_put fix for multicast
  16  *                                      routing.
  17  *              Jos Vos         :       Add call_out_firewall before sending,
  18  *                                      use output device for accounting.
  19  *              Jos Vos         :       Call forward firewall after routing
  20  *                                      (always use output device).
  21  *              Mike McLagan    :       Routing by source
  22  */
  23
  24 #include <linux/config.h>
  25 #include <linux/types.h>
  26 #include <linux/mm.h>
  27 #include <linux/sched.h>
  28 #include <linux/skbuff.h>
  29 #include <linux/ip.h>
  30 #include <linux/icmp.h>
  31 #include <linux/netdevice.h>
  32 #include <net/sock.h>
  33 #include <net/ip.h>
  34 #include <net/tcp.h>
  35 #include <net/udp.h>
  36 #include <net/icmp.h>
  37 #include <linux/tcp.h>
  38 #include <linux/udp.h>
  39 #include <linux/firewall.h>
  40 #include <linux/ip_fw.h>
  41 #ifdef CONFIG_IP_MASQUERADE
  42 #include <net/ip_masq.h>
  43 #endif
  44 #include <net/checksum.h>
  45 #include <linux/route.h>
  46 #include <net/route.h>
  47
  48 #ifdef CONFIG_IP_TRANSPARENT_PROXY
  49 /*
  50  *      Check the packet against our socket administration to see
  51  *      if it is related to a connection on our system.
  52  *      Needed for transparent proxying.
  53  */
  54
  55 int ip_chksock(struct sk_buff *skb)
  56 {
  57         switch (skb->nh.iph->protocol) {
  58         case IPPROTO_ICMP:
  59                 return icmp_chkaddr(skb);
  60         case IPPROTO_TCP:
  61                 return tcp_chkaddr(skb);
  62         case IPPROTO_UDP:
  63                 return udp_chkaddr(skb);
  64         default:
  65                 return 0;
  66         }
  67 }
  68 #endif
  69
  70
  71 int ip_forward(struct sk_buff *skb)
  72 {
  73         struct device *dev2;    /* Output device */
  74         struct iphdr *iph;      /* Our header */
  75         struct rtable *rt;      /* Route we use */
  76         struct ip_options * opt = &(IPCB(skb)->opt);
  77         unsigned short mtu;
  78 #if defined(CONFIG_FIREWALL) || defined(CONFIG_IP_MASQUERADE)
  79         int fw_res = 0;
  80 #endif
  81
  82         if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb))
  83                 return 0;
  84
  85         if (skb->pkt_type != PACKET_HOST)
  86                 goto drop;
  87
  88         /*
  89          *      According to the RFC, we must first decrease the TTL field. If
  90          *      that reaches zero, we must reply an ICMP control message telling
  91          *      that the packet's lifetime expired.
  92          */
  93
  94         iph = skb->nh.iph;
  95         rt = (struct rtable*)skb->dst;
  96
  97 #ifdef CONFIG_CPU_IS_SLOW
  98         if (net_cpu_congestion > 1 && !(iph->tos&IPTOS_RELIABILITY) &&
  99             IPTOS_PREC(iph->tos) < IPTOS_PREC_INTERNETCONTROL) {
 100                 if (((xtime.tv_usec&0xF)<<net_cpu_congestion) > 0x1C)
 101                         goto drop;
 102         }
 103 #endif
 104
 105
 106 #ifdef CONFIG_IP_TRANSPARENT_PROXY
 107         if (ip_chksock(skb))
 108                 goto local_pkt;
 109 #endif
 110
 111         if (iph->ttl <= 1)
 112                 goto too_many_hops;
 113
 114         if (opt->is_strictroute && rt->rt_dst != rt->rt_gateway)
 115                 goto sr_failed;
 116
 117         /*
 118          *      Having picked a route we can now send the frame out
 119          *      after asking the firewall permission to do so.
 120          */
 121
 122         skb->priority = rt_tos2priority(iph->tos);
 123         dev2 = rt->u.dst.dev;
 124         mtu = rt->u.dst.pmtu;
 125
 126 #ifdef CONFIG_NET_SECURITY
 127         call_fw_firewall(PF_SECURITY, dev2, NULL, &mtu, NULL);
 128 #endif
 129
 130         /*
 131          *      We now generate an ICMP HOST REDIRECT giving the route
 132          *      we calculated.
 133          */
 134         if (rt->rt_flags&RTCF_DOREDIRECT && !opt->srr)
 135                 ip_rt_send_redirect(skb);
 136
 137         /* We are about to mangle packet. Copy it! */
 138         if ((skb = skb_cow(skb, dev2->hard_header_len)) == NULL)
 139                 return -1;
 140         iph = skb->nh.iph;
 141         opt = &(IPCB(skb)->opt);
 142
 143         /* Decrease ttl after skb cow done */
 144         ip_decrease_ttl(iph);
 145
 146         /*
 147          * We now may allocate a new buffer, and copy the datagram into it.
 148          * If the indicated interface is up and running, kick it.
 149          */
 150
 151         if (skb->len > mtu && (ntohs(iph->frag_off) & IP_DF))
 152                 goto frag_needed;
 153
 154 #ifdef CONFIG_IP_ROUTE_NAT
 155         if (rt->rt_flags & RTCF_NAT) {
 156                 if (ip_do_nat(skb)) {
 157                         kfree_skb(skb);
 158                         return -1;
 159                 }
 160         }
 161 #endif
 162
 163 #ifdef CONFIG_IP_MASQUERADE
 164         if(!(IPCB(skb)->flags&IPSKB_MASQUERADED)) {
 165                 /*
 166                  *      Check that any ICMP packets are not for a
 167                  *      masqueraded connection.  If so rewrite them
 168                  *      and skip the firewall checks
 169                  */
 170                 if (iph->protocol == IPPROTO_ICMP) {
 171                         __u32 maddr;
 172 #ifdef CONFIG_IP_MASQUERADE_ICMP
 173                         struct icmphdr *icmph = (struct icmphdr *)((char*)iph + (iph->ihl << 2));
 174                         if ((icmph->type==ICMP_DEST_UNREACH)||
 175                             (icmph->type==ICMP_SOURCE_QUENCH)||
 176                             (icmph->type==ICMP_TIME_EXCEEDED))
 177                         {
 178 #endif
 179                                 maddr = inet_select_addr(dev2, rt->rt_gateway, RT_SCOPE_UNIVERSE);
 180                                 fw_res = ip_fw_masq_icmp(&skb, maddr);
 181                                 if (fw_res < 0) {
 182                                         kfree_skb(skb);
 183                                         return -1;
 184                                 }
 185
 186                                 if (fw_res)
 187                                         /* ICMP matched - skip firewall */
 188                                         goto skip_call_fw_firewall;
 189 #ifdef CONFIG_IP_MASQUERADE_ICMP
 190                                }
 191 #endif
 192                 }
 193                 if (rt->rt_flags&RTCF_MASQ)
 194                         goto skip_call_fw_firewall;
 195 #endif /* CONFIG_IP_MASQUERADE */
 196
 197 #ifdef CONFIG_FIREWALL
 198                 fw_res=call_fw_firewall(PF_INET, dev2, iph, NULL, &skb);
 199                 switch (fw_res) {
 200                 case FW_ACCEPT:
 201                 case FW_MASQUERADE:
 202                         break;
 203                 case FW_REJECT:
 204                         icmp_send(skb, ICMP_DEST_UNREACH, ICMP_HOST_UNREACH, 0);
 205                         /* fall thru */
 206                 default:
 207                         kfree_skb(skb);
 208                         return -1;
 209                 }
 210 #endif
 211
 212 #ifdef CONFIG_IP_MASQUERADE
 213         }
 214
 215 skip_call_fw_firewall:
 216         /*
 217          * If this fragment needs masquerading, make it so...
 218          * (Don't masquerade de-masqueraded fragments)
 219          */
 220         if (!(IPCB(skb)->flags&IPSKB_MASQUERADED) &&
 221             (fw_res==FW_MASQUERADE || rt->rt_flags&RTCF_MASQ)) {
 222                 u32 maddr;
 223
 224 #ifdef CONFIG_IP_ROUTE_NAT
 225                 maddr = (rt->rt_flags&RTCF_MASQ) ? rt->rt_src_map : 0;
 226
 227                 if (maddr == 0)
 228 #endif
 229                         maddr = inet_select_addr(dev2, rt->rt_gateway, RT_SCOPE_UNIVERSE);
 230
 231                         if (ip_fw_masquerade(&skb, maddr) < 0) {
 232                                 kfree_skb(skb);
 233                                 return -1;
 234                         } else {
 235                                 /*
 236                                  *      Masquerader may have changed skb
 237                                  */
 238                                 iph = skb->nh.iph;
 239                                 opt = &(IPCB(skb)->opt);
 240                         }
 241         }
 242 #endif
 243
 244
 245 #ifdef CONFIG_FIREWALL
 246         if ((fw_res = call_out_firewall(PF_INET, dev2, iph, NULL,&skb)) < FW_ACCEPT) {
 247                 /* FW_ACCEPT and FW_MASQUERADE are treated equal:
 248                    masquerading is only supported via forward rules */
 249                 if (fw_res == FW_REJECT)
 250                         icmp_send(skb, ICMP_DEST_UNREACH, ICMP_HOST_UNREACH, 0);
 251                 kfree_skb(skb);
 252                 return -1;
 253         }
 254 #endif
 255
 256         ip_statistics.IpForwDatagrams++;
 257
 258         if (opt->optlen == 0) {
 259 #ifdef CONFIG_NET_FASTROUTE
 260                 if (rt->rt_flags&RTCF_FAST && !netdev_fastroute_obstacles) {
 261                         unsigned h = ((*(u8*)&rt->key.dst)^(*(u8*)&rt->key.src))&NETDEV_FASTROUTE_HMASK;
 262                         /* Time to switch to functional programming :-) */
 263                         dst_release_irqwait(xchg(&skb->dev->fastpath[h], dst_clone(&rt->u.dst)));
 264                 }
 265 #endif
 266                 ip_send(skb);
 267                 return 0;
 268         }
 269
 270         ip_forward_options(skb);
 271         ip_send(skb);
 272         return 0;
 273
 274 #ifdef CONFIG_IP_TRANSPARENT_PROXY
 275 local_pkt:
 276         return ip_local_deliver(skb);
 277 #endif
 278
 279 frag_needed:
 280         ip_statistics.IpFragFails++;
 281         icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, htonl(mtu));
 282         goto drop;
 283
 284 sr_failed:
 285         /*
 286          *      Strict routing permits no gatewaying
 287          */
 288          icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0);
 289          goto drop;
 290
 291 too_many_hops:
 292         /* Tell the sender its packet died... */
 293         icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0);
 294 drop:
 295         kfree_skb(skb);
 296         return -1;
 297 }