| /* |
| * 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 bool ip_may_fragment(const struct sk_buff *skb) |
| { |
| return unlikely((ip_hdr(skb)->frag_off & htons(IP_DF)) == 0) || |
| !skb->local_df; |
| } |
| |
| static bool ip_exceeds_mtu(const struct sk_buff *skb, unsigned int mtu) |
| { |
| if (skb->len <= mtu || skb->local_df) |
| return false; |
| |
| if (skb_is_gso(skb) && skb_gso_network_seglen(skb) <= mtu) |
| return false; |
| |
| return true; |
| } |
| |
| static bool ip_gso_exceeds_dst_mtu(const struct sk_buff *skb) |
| { |
| unsigned int mtu; |
| |
| if (skb->local_df || !skb_is_gso(skb)) |
| return false; |
| |
| mtu = dst_mtu(skb_dst(skb)); |
| |
| /* if seglen > mtu, do software segmentation for IP fragmentation on |
| * output. DF bit cannot be set since ip_forward would have sent |
| * icmp error. |
| */ |
| return skb_gso_network_seglen(skb) > mtu; |
| } |
| |
| /* called if GSO skb needs to be fragmented on forward */ |
| static int ip_forward_finish_gso(struct sk_buff *skb) |
| { |
| struct sk_buff *segs; |
| int ret = 0; |
| |
| segs = skb_gso_segment(skb, 0); |
| if (IS_ERR(segs)) { |
| kfree_skb(skb); |
| return -ENOMEM; |
| } |
| |
| consume_skb(skb); |
| |
| do { |
| struct sk_buff *nskb = segs->next; |
| int err; |
| |
| segs->next = NULL; |
| err = dst_output(segs); |
| |
| if (err && ret == 0) |
| ret = err; |
| segs = nskb; |
| } while (segs); |
| |
| return ret; |
| } |
| |
| 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); |
| |
| if (ip_gso_exceeds_dst_mtu(skb)) |
| return ip_forward_finish_gso(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 && opt->nexthop != rt->rt_gateway) |
| goto sr_failed; |
| |
| if (!ip_may_fragment(skb) && ip_exceeds_mtu(skb, dst_mtu(&rt->dst))) { |
| 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 (IPCB(skb)->flags & IPSKB_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; |
| } |