2 * INET An implementation of the TCP/IP protocol suite for the LINUX
3 * operating system. INET is implemented using the BSD Socket
4 * interface as the means of communication with the user level.
6 * The IP forwarding functionality.
11 * Many : Split from ip.c , see ip_input.c for
13 * Dave Gregorich : NULL ip_rt_put fix for multicast
15 * Jos Vos : Add call_out_firewall before sending,
16 * use output device for accounting.
17 * Jos Vos : Call forward firewall after routing
18 * (always use output device).
19 * Mike McLagan : Routing by source
22 #include <linux/types.h>
24 #include <linux/skbuff.h>
26 #include <linux/icmp.h>
27 #include <linux/netdevice.h>
28 #include <linux/slab.h>
34 #include <linux/tcp.h>
35 #include <linux/udp.h>
36 #include <linux/netfilter_ipv4.h>
37 #include <net/checksum.h>
38 #include <linux/route.h>
39 #include <net/route.h>
42 static bool ip_may_fragment(const struct sk_buff *skb)
44 return unlikely((ip_hdr(skb)->frag_off & htons(IP_DF)) == 0) ||
48 static bool ip_exceeds_mtu(const struct sk_buff *skb, unsigned int mtu)
50 if (skb->len <= mtu || skb->local_df)
53 if (skb_is_gso(skb) && skb_gso_network_seglen(skb) <= mtu)
59 static bool ip_gso_exceeds_dst_mtu(const struct sk_buff *skb)
63 if (skb->local_df || !skb_is_gso(skb))
66 mtu = dst_mtu(skb_dst(skb));
68 /* if seglen > mtu, do software segmentation for IP fragmentation on
69 * output. DF bit cannot be set since ip_forward would have sent
72 return skb_gso_network_seglen(skb) > mtu;
75 /* called if GSO skb needs to be fragmented on forward */
76 static int ip_forward_finish_gso(struct sk_buff *skb)
81 segs = skb_gso_segment(skb, 0);
90 struct sk_buff *nskb = segs->next;
94 err = dst_output(segs);
104 static int ip_forward_finish(struct sk_buff *skb)
106 struct ip_options * opt = &(IPCB(skb)->opt);
108 IP_INC_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_OUTFORWDATAGRAMS);
110 if (unlikely(opt->optlen))
111 ip_forward_options(skb);
113 if (ip_gso_exceeds_dst_mtu(skb))
114 return ip_forward_finish_gso(skb);
116 return dst_output(skb);
119 int ip_forward(struct sk_buff *skb)
121 struct iphdr *iph; /* Our header */
122 struct rtable *rt; /* Route we use */
123 struct ip_options * opt = &(IPCB(skb)->opt);
125 if (skb_warn_if_lro(skb))
128 if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb))
131 if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb))
132 return NET_RX_SUCCESS;
134 if (skb->pkt_type != PACKET_HOST)
137 skb_forward_csum(skb);
140 * According to the RFC, we must first decrease the TTL field. If
141 * that reaches zero, we must reply an ICMP control message telling
142 * that the packet's lifetime expired.
144 if (ip_hdr(skb)->ttl <= 1)
147 if (!xfrm4_route_forward(skb))
150 rt = skb_rtable(skb);
152 if (opt->is_strictroute && opt->nexthop != rt->rt_gateway)
155 if (!ip_may_fragment(skb) && ip_exceeds_mtu(skb, dst_mtu(&rt->dst))) {
156 IP_INC_STATS(dev_net(rt->dst.dev), IPSTATS_MIB_FRAGFAILS);
157 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
158 htonl(dst_mtu(&rt->dst)));
162 /* We are about to mangle packet. Copy it! */
163 if (skb_cow(skb, LL_RESERVED_SPACE(rt->dst.dev)+rt->dst.header_len))
167 /* Decrease ttl after skb cow done */
168 ip_decrease_ttl(iph);
171 * We now generate an ICMP HOST REDIRECT giving the route
174 if (rt->rt_flags&RTCF_DOREDIRECT && !opt->srr && !skb_sec_path(skb))
175 ip_rt_send_redirect(skb);
177 skb->priority = rt_tos2priority(iph->tos);
179 return NF_HOOK(NFPROTO_IPV4, NF_INET_FORWARD, skb, skb->dev,
180 rt->dst.dev, ip_forward_finish);
184 * Strict routing permits no gatewaying
186 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0);
190 /* Tell the sender its packet died... */
191 IP_INC_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_INHDRERRORS);
192 icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0);