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/*

 * INET         An implementation of the TCP/IP protocol suite for the LINUX

 *              operating system.  INET is implemented using the  BSD Socket

 *              interface as the means of communication with the user level.

 *

 *              The IP forwarding functionality.

 *

 * Version:     $Id: ip_forward.c,v 1.1.1.1 2004-04-15 01:13:57 phoenix Exp $

 *

 * Authors:     see ip.c

 *

 * Fixes:

 *              Many            :       Split from ip.c , see ip_input.c for

 *                                      history.

 *              Dave Gregorich  :       NULL ip_rt_put fix for multicast

 *                                      routing.

 *              Jos Vos         :       Add call_out_firewall before sending,

 *                                      use output device for accounting.

 *              Jos Vos         :       Call forward firewall after routing

 *                                      (always use output device).

 *              Mike McLagan    :       Routing by source

 */

#include <linux/config.h>

#include <linux/types.h>

#include <linux/mm.h>

#include <linux/sched.h>

#include <linux/skbuff.h>

#include <linux/ip.h>

#include <linux/icmp.h>

#include <linux/netdevice.h>

#include <net/sock.h>

#include <net/ip.h>

#include <net/tcp.h>

#include <net/udp.h>

#include <net/icmp.h>

#include <linux/tcp.h>

#include <linux/udp.h>

#include <linux/netfilter_ipv4.h>

#include <net/checksum.h>

#include <linux/route.h>

#include <net/route.h>

static inline int ip_forward_finish(struct sk_buff *skb)

{

        struct ip_options * opt = &(IPCB(skb)->opt);

        IP_INC_STATS_BH(IpForwDatagrams);

        if (opt->optlen == 0) {

#ifdef CONFIG_NET_FASTROUTE

                struct rtable *rt = (struct rtable*)skb->dst;

                if (rt->rt_flags&RTCF_FAST && !netdev_fastroute_obstacles) {

                        struct dst_entry *old_dst;

                        unsigned h = ((*(u8*)&rt->key.dst)^(*(u8*)&rt->key.src))&NETDEV_FASTROUTE_HMASK;

                        write_lock_irq(&skb->dev->fastpath_lock);

                        old_dst = skb->dev->fastpath[h];

                        skb->dev->fastpath[h] = dst_clone(&rt->u.dst);

                        write_unlock_irq(&skb->dev->fastpath_lock);

                        dst_release(old_dst);

                }

#endif

                return (ip_send(skb));

        }

        ip_forward_options(skb);

        return (ip_send(skb));

}

int ip_forward(struct sk_buff *skb)

{

        struct net_device *dev2;        /* Output device */

        struct iphdr *iph;      /* Our header */

        struct rtable *rt;      /* Route we use */

        struct ip_options * opt = &(IPCB(skb)->opt);

        unsigned short mtu;

        if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb))

                return NET_RX_SUCCESS;

        if (skb->pkt_type != PACKET_HOST)

                goto drop;

        skb->ip_summed = CHECKSUM_NONE;

        /*

         *      According to the RFC, we must first decrease the TTL field. If

         *      that reaches zero, we must reply an ICMP control message telling

         *      that the packet's lifetime expired.

         */

        iph = skb->nh.iph;

        rt = (struct rtable*)skb->dst;

        if (iph->ttl <= 1)

                goto too_many_hops;

        if (opt->is_strictroute && rt->rt_dst != rt->rt_gateway)

                goto sr_failed;

        /*

         *      Having picked a route we can now send the frame out

         *      after asking the firewall permission to do so.

         */

        skb->priority = rt_tos2priority(iph->tos);

        dev2 = rt->u.dst.dev;

        mtu = rt->u.dst.pmtu;

        /*

         *      We now generate an ICMP HOST REDIRECT giving the route

         *      we calculated.

         */

        if (rt->rt_flags&RTCF_DOREDIRECT && !opt->srr)

                ip_rt_send_redirect(skb);

        /* We are about to mangle packet. Copy it! */

        if (skb_cow(skb, dev2->hard_header_len))

                goto drop;

        iph = skb->nh.iph;

        /* Decrease ttl after skb cow done */

        ip_decrease_ttl(iph);

        /*

         * We now may allocate a new buffer, and copy the datagram into it.

         * If the indicated interface is up and running, kick it.

         */

        if (skb->len > mtu && (ntohs(iph->frag_off) & IP_DF))

                goto frag_needed;

#ifdef CONFIG_IP_ROUTE_NAT

        if (rt->rt_flags & RTCF_NAT) {

                if (ip_do_nat(skb)) {

                        kfree_skb(skb);

                        return NET_RX_BAD;

                }

        }

#endif

        return NF_HOOK(PF_INET, NF_IP_FORWARD, skb, skb->dev, dev2,

                       ip_forward_finish);

frag_needed:

        IP_INC_STATS_BH(IpFragFails);

        icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, htonl(mtu));

        goto drop;

sr_failed:

        /*

         *      Strict routing permits no gatewaying

         */

         icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0);

         goto drop;

too_many_hops:

        /* Tell the sender its packet died... */

        icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0);

drop:

        kfree_skb(skb);

        return NET_RX_DROP;

}