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| 2 | |
| 3 | * INET An implementation of the TCP/IP protocol suite for the LINUX
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| 4 | * operating system. INET is implemented using the BSD Socket
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| 5 | * interface as the means of communication with the user level.
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| 6 | *
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| 7 | * The IP forwarding functionality.
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| 8 | *
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| 9 | * Authors: see ip.c
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| 10 | *
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| 11 | * Fixes:
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| 12 | * Many : Split from ip.c , see ip_input.c for
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| 13 | * history.
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| 14 | * Dave Gregorich : NULL ip_rt_put fix for multicast
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| 15 | * routing.
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| 16 | * Jos Vos : Add call_out_firewall before sending,
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| 17 | * use output device for accounting.
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| 18 | * Jos Vos : Call forward firewall after routing
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| 19 | * (always use output device).
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| 20 | * Mike McLagan : Routing by source
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| 21 |
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| 22 |
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| 23 | #include <linux/types.h>
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| 24 | #include <linux/mm.h>
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| 25 | #include <linux/skbuff.h>
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| 26 | #include <linux/ip.h>
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| 27 | #include <linux/icmp.h>
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| 28 | #include <linux/netdevice.h>
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| 29 | #include <linux/slab.h>
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| 30 | #include <net/sock.h>
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| 31 | #include <net/ip.h>
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| 32 | #include <net/tcp.h>
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| 33 | #include <net/udp.h>
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| 34 | #include <net/icmp.h>
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| 35 | #include <linux/tcp.h>
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| 36 | #include <linux/udp.h>
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| 37 | #include <linux/netfilter_ipv4.h>
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| 38 | #include <net/checksum.h>
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| 39 | #include <linux/route.h>
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| 40 | #include <net/route.h>
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| 41 | #include <net/xfrm.h>
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| 42 |
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| 43 | static bool ip_exceeds_mtu(const struct sk_buff *skb, unsigned int mtu)
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| 44 | {
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| 45 | if (skb->len <= mtu)
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| 46 | return false;
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| 47 |
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| 48 | if (unlikely((ip_hdr(skb)->frag_off & htons(IP_DF)) == 0))
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| 49 | return false;
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| 50 |
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| 51 |
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| 52 | if (unlikely(IPCB(skb)->frag_max_size > mtu))
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| 53 | return true;
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| 54 |
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| 55 | if (skb->ignore_df)
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| 56 | return false;
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| 57 |
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| 58 | if (skb_is_gso(skb) && skb_gso_validate_network_len(skb, mtu))
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| 59 | return false;
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| 60 |
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| 61 | return true;
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| 62 | }
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| 63 |
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| 64 |
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| 65 | static int ip_forward_finish(struct net *net, struct sock *sk, struct sk_buff *skb)
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| 66 | {
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| 67 | struct ip_options *opt = &(IPCB(skb)->opt);
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| 68 |
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| 69 | #ifdef CONFIG_NET_SWITCHDEV
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| 70 | if (skb->offload_l3_fwd_mark) {
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| 71 | consume_skb(skb);
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| 72 | return 0;
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| 73 | }
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| 74 | #endif
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| 75 |
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| 76 | if (unlikely(opt->optlen))
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| 77 | ip_forward_options(skb);
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| 78 |
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| 79 | skb_clear_tstamp(skb);
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| 80 | return dst_output(net, sk, skb);
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| 81 | }
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| 82 |
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| 83 | int ip_forward(struct sk_buff *skb)
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| 84 | {
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| 85 | u32 mtu;
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| 86 | struct iphdr *iph;
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| 87 | struct rtable *rt;
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| 88 | struct ip_options *opt = &(IPCB(skb)->opt);
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| 89 | struct net *net;
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| 90 | SKB_DR(reason);
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| 91 |
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| 92 |
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| 93 | if (skb->pkt_type != PACKET_HOST)
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| 94 | goto drop;
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| 95 |
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| 96 | if (unlikely(skb->sk))
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| 97 | goto drop;
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| 98 |
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| 99 | if (skb_warn_if_lro(skb))
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| 100 | goto drop;
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| 101 |
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| 102 | if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb)) {
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| 103 | SKB_DR_SET(reason, XFRM_POLICY);
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| 104 | goto drop;
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| 105 | }
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| 106 |
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| 107 | if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb))
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| 108 | return NET_RX_SUCCESS;
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| 109 |
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| 110 | skb_forward_csum(skb);
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| 111 | net = dev_net(skb->dev);
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| 112 |
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| 113 | |
| 114 | * According to the RFC, we must first decrease the TTL field. If
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| 115 | * that reaches zero, we must reply an ICMP control message telling
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| 116 | * that the packet's lifetime expired.
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| 117 |
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| 118 | if (ip_hdr(skb)->ttl <= 1)
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| 119 | goto too_many_hops;
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| 120 |
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| 121 | if (!xfrm4_route_forward(skb)) {
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| 122 | SKB_DR_SET(reason, XFRM_POLICY);
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| 123 | goto drop;
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| 124 | }
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| 125 |
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| 126 | rt = skb_rtable(skb);
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| 127 |
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| 128 | if (opt->is_strictroute && rt->rt_uses_gateway)
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| 129 | goto sr_failed;
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| 130 |
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| 131 | __IP_INC_STATS(net, IPSTATS_MIB_OUTFORWDATAGRAMS);
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| 132 |
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| 133 | IPCB(skb)->flags |= IPSKB_FORWARDED;
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| 134 | mtu = ip_dst_mtu_maybe_forward(&rt->dst, true);
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| 135 | if (ip_exceeds_mtu(skb, mtu)) {
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| 136 | IP_INC_STATS(net, IPSTATS_MIB_FRAGFAILS);
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| 137 | icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
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| 138 | htonl(mtu));
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| 139 | SKB_DR_SET(reason, PKT_TOO_BIG);
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| 140 | goto drop;
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| 141 | }
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| 142 |
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| 143 |
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| 144 | if (skb_cow(skb, LL_RESERVED_SPACE(rt->dst.dev)+rt->dst.header_len))
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| 145 | goto drop;
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| 146 | iph = ip_hdr(skb);
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| 147 |
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| 148 |
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| 149 | ip_decrease_ttl(iph);
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| 150 |
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| 151 | |
| 152 | * We now generate an ICMP HOST REDIRECT giving the route
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| 153 | * we calculated.
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| 154 |
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| 155 | if (IPCB(skb)->flags & IPSKB_DOREDIRECT && !opt->srr &&
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| 156 | !skb_sec_path(skb))
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| 157 | ip_rt_send_redirect(skb);
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| 158 |
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| 159 | if (READ_ONCE(net->ipv4.sysctl_ip_fwd_update_priority))
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| 160 | skb->priority = rt_tos2priority(iph->tos);
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| 161 |
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| 162 | return NF_HOOK(NFPROTO_IPV4, NF_INET_FORWARD,
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| 163 | net, NULL, skb, skb->dev, rt->dst.dev,
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| 164 | ip_forward_finish);
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| 165 |
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| 166 | sr_failed:
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| 167 | |
| 168 | * Strict routing permits no gatewaying
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| 169 |
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| 170 | icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0);
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| 171 | goto drop;
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| 172 |
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| 173 | too_many_hops:
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| 174 |
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| 175 | __IP_INC_STATS(net, IPSTATS_MIB_INHDRERRORS);
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| 176 | icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0);
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| 177 | SKB_DR_SET(reason, IP_INHDR);
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| 178 | drop:
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| 179 | kfree_skb_reason(skb, reason);
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| 180 | return NET_RX_DROP;
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| 181 | }
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