167 lines
3.9 KiB
C
167 lines
3.9 KiB
C
/*
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* INET An implementation of the TCP/IP protocol suite for the LINUX
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* operating system. INET is implemented using the BSD Socket
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* interface as the means of communication with the user level.
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*
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* The IP forwarding functionality.
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*
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* Authors: see ip.c
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*
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* Fixes:
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* Many : Split from ip.c , see ip_input.c for
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* history.
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* Dave Gregorich : NULL ip_rt_put fix for multicast
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* routing.
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* Jos Vos : Add call_out_firewall before sending,
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* use output device for accounting.
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* Jos Vos : Call forward firewall after routing
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* (always use output device).
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* Mike McLagan : Routing by source
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*/
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#include <linux/types.h>
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#include <linux/mm.h>
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#include <linux/skbuff.h>
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#include <linux/ip.h>
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#include <linux/icmp.h>
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#include <linux/netdevice.h>
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#include <linux/slab.h>
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#include <net/sock.h>
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#include <net/ip.h>
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#include <net/tcp.h>
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#include <net/udp.h>
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#include <net/icmp.h>
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#include <linux/tcp.h>
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#include <linux/udp.h>
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#include <linux/netfilter_ipv4.h>
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#include <net/checksum.h>
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#include <linux/route.h>
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#include <net/route.h>
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#include <net/xfrm.h>
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static bool ip_exceeds_mtu(const struct sk_buff *skb, unsigned int mtu)
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{
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if (skb->len <= mtu)
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return false;
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if (unlikely((ip_hdr(skb)->frag_off & htons(IP_DF)) == 0))
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return false;
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/* original fragment exceeds mtu and DF is set */
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if (unlikely(IPCB(skb)->frag_max_size > mtu))
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return true;
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if (skb->ignore_df)
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return false;
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if (skb_is_gso(skb) && skb_gso_network_seglen(skb) <= mtu)
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return false;
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return true;
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}
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static int ip_forward_finish(struct net *net, struct sock *sk, struct sk_buff *skb)
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{
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struct ip_options *opt = &(IPCB(skb)->opt);
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IP_INC_STATS_BH(net, IPSTATS_MIB_OUTFORWDATAGRAMS);
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IP_ADD_STATS_BH(net, IPSTATS_MIB_OUTOCTETS, skb->len);
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if (unlikely(opt->optlen))
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ip_forward_options(skb);
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skb_sender_cpu_clear(skb);
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return dst_output(net, sk, skb);
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}
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int ip_forward(struct sk_buff *skb)
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{
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u32 mtu;
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struct iphdr *iph; /* Our header */
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struct rtable *rt; /* Route we use */
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struct ip_options *opt = &(IPCB(skb)->opt);
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struct net *net;
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/* that should never happen */
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if (skb->pkt_type != PACKET_HOST)
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goto drop;
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if (unlikely(skb->sk))
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goto drop;
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if (skb_warn_if_lro(skb))
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goto drop;
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if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb))
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goto drop;
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if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb))
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return NET_RX_SUCCESS;
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skb_forward_csum(skb);
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net = dev_net(skb->dev);
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/*
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* According to the RFC, we must first decrease the TTL field. If
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* that reaches zero, we must reply an ICMP control message telling
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* that the packet's lifetime expired.
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*/
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if (ip_hdr(skb)->ttl <= 1)
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goto too_many_hops;
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if (!xfrm4_route_forward(skb))
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goto drop;
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rt = skb_rtable(skb);
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if (opt->is_strictroute && rt->rt_uses_gateway)
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goto sr_failed;
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IPCB(skb)->flags |= IPSKB_FORWARDED;
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mtu = ip_dst_mtu_maybe_forward(&rt->dst, true);
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if (ip_exceeds_mtu(skb, mtu)) {
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IP_INC_STATS(net, IPSTATS_MIB_FRAGFAILS);
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icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
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htonl(mtu));
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goto drop;
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}
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/* We are about to mangle packet. Copy it! */
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if (skb_cow(skb, LL_RESERVED_SPACE(rt->dst.dev)+rt->dst.header_len))
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goto drop;
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iph = ip_hdr(skb);
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/* Decrease ttl after skb cow done */
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ip_decrease_ttl(iph);
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/*
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* We now generate an ICMP HOST REDIRECT giving the route
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* we calculated.
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*/
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if (IPCB(skb)->flags & IPSKB_DOREDIRECT && !opt->srr &&
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!skb_sec_path(skb))
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ip_rt_send_redirect(skb);
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skb->priority = rt_tos2priority(iph->tos);
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return NF_HOOK(NFPROTO_IPV4, NF_INET_FORWARD,
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net, NULL, skb, skb->dev, rt->dst.dev,
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ip_forward_finish);
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sr_failed:
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/*
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* Strict routing permits no gatewaying
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*/
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icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0);
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goto drop;
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too_many_hops:
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/* Tell the sender its packet died... */
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IP_INC_STATS_BH(net, IPSTATS_MIB_INHDRERRORS);
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icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0);
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drop:
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kfree_skb(skb);
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return NET_RX_DROP;
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}
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