/* * 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 1.48 2000/12/13 18:31:48 davem 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;}