/* * 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. * * 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/types.h> #include <linux/mm.h> #include <linux/skbuff.h> #include <linux/ip.h> #include <linux/icmp.h> #include <linux/netdevice.h> #include <linux/slab.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> #include <net/xfrm.h> static int ip_forward_finish(struct sk_buff *skb) { struct ip_options * opt = &(IPCB(skb)->opt); IP_INC_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_OUTFORWDATAGRAMS); if (unlikely(opt->optlen)) ip_forward_options(skb); return dst_output(skb); } int ip_forward(struct sk_buff *skb) { struct iphdr *iph; /* Our header */ struct rtable *rt; /* Route we use */ struct ip_options * opt = &(IPCB(skb)->opt); if (skb_warn_if_lro(skb)) goto drop; if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb)) goto drop; if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb)) return NET_RX_SUCCESS; if (skb->pkt_type != PACKET_HOST) goto drop; skb_forward_csum(skb); /* * 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. */ if (ip_hdr(skb)->ttl <= 1) goto too_many_hops; if (!xfrm4_route_forward(skb)) goto drop; rt = skb_rtable(skb); if (opt->is_strictroute && rt->rt_dst != rt->rt_gateway) goto sr_failed; if (unlikely(skb->len > dst_mtu(&rt->dst) && !skb_is_gso(skb) && (ip_hdr(skb)->frag_off & htons(IP_DF))) && !skb->local_df) { IP_INC_STATS(dev_net(rt->dst.dev), IPSTATS_MIB_FRAGFAILS); icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, htonl(dst_mtu(&rt->dst))); goto drop; } /* We are about to mangle packet. Copy it! */ if (skb_cow(skb, LL_RESERVED_SPACE(rt->dst.dev)+rt->dst.header_len)) goto drop; iph = ip_hdr(skb); /* Decrease ttl after skb cow done */ ip_decrease_ttl(iph); /* * We now generate an ICMP HOST REDIRECT giving the route * we calculated. */ if (rt->rt_flags&RTCF_DOREDIRECT && !opt->srr && !skb_sec_path(skb)) ip_rt_send_redirect(skb); skb->priority = rt_tos2priority(iph->tos); return NF_HOOK(NFPROTO_IPV4, NF_INET_FORWARD, skb, skb->dev, rt->dst.dev, ip_forward_finish); 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... */ IP_INC_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_INHDRERRORS); icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0); drop: kfree_skb(skb); return NET_RX_DROP; }