diff options
Diffstat (limited to 'net/ipv4/ip_forward.c')
| -rw-r--r-- | net/ipv4/ip_forward.c | 182 |
1 files changed, 182 insertions, 0 deletions
diff --git a/net/ipv4/ip_forward.c b/net/ipv4/ip_forward.c new file mode 100644 index 000000000..e18931a6d --- /dev/null +++ b/net/ipv4/ip_forward.c @@ -0,0 +1,182 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * 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_exceeds_mtu(const struct sk_buff *skb, unsigned int mtu) +{ + if (skb->len <= mtu) + return false; + + if (unlikely((ip_hdr(skb)->frag_off & htons(IP_DF)) == 0)) + return false; + + /* original fragment exceeds mtu and DF is set */ + if (unlikely(IPCB(skb)->frag_max_size > mtu)) + return true; + + if (skb->ignore_df) + return false; + + if (skb_is_gso(skb) && skb_gso_validate_network_len(skb, mtu)) + return false; + + return true; +} + + +static int ip_forward_finish(struct net *net, struct sock *sk, struct sk_buff *skb) +{ + struct ip_options *opt = &(IPCB(skb)->opt); + + __IP_INC_STATS(net, IPSTATS_MIB_OUTFORWDATAGRAMS); + __IP_ADD_STATS(net, IPSTATS_MIB_OUTOCTETS, skb->len); + +#ifdef CONFIG_NET_SWITCHDEV + if (skb->offload_l3_fwd_mark) { + consume_skb(skb); + return 0; + } +#endif + + if (unlikely(opt->optlen)) + ip_forward_options(skb); + + skb_clear_tstamp(skb); + return dst_output(net, sk, skb); +} + +int ip_forward(struct sk_buff *skb) +{ + u32 mtu; + struct iphdr *iph; /* Our header */ + struct rtable *rt; /* Route we use */ + struct ip_options *opt = &(IPCB(skb)->opt); + struct net *net; + SKB_DR(reason); + + /* that should never happen */ + if (skb->pkt_type != PACKET_HOST) + goto drop; + + if (unlikely(skb->sk)) + goto drop; + + if (skb_warn_if_lro(skb)) + goto drop; + + if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb)) { + SKB_DR_SET(reason, XFRM_POLICY); + goto drop; + } + + if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb)) + return NET_RX_SUCCESS; + + skb_forward_csum(skb); + net = dev_net(skb->dev); + + /* + * 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)) { + SKB_DR_SET(reason, XFRM_POLICY); + goto drop; + } + + rt = skb_rtable(skb); + + if (opt->is_strictroute && rt->rt_uses_gateway) + goto sr_failed; + + IPCB(skb)->flags |= IPSKB_FORWARDED; + mtu = ip_dst_mtu_maybe_forward(&rt->dst, true); + if (ip_exceeds_mtu(skb, mtu)) { + IP_INC_STATS(net, IPSTATS_MIB_FRAGFAILS); + icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, + htonl(mtu)); + SKB_DR_SET(reason, PKT_TOO_BIG); + 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); + + if (READ_ONCE(net->ipv4.sysctl_ip_fwd_update_priority)) + skb->priority = rt_tos2priority(iph->tos); + + return NF_HOOK(NFPROTO_IPV4, NF_INET_FORWARD, + net, NULL, 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(net, IPSTATS_MIB_INHDRERRORS); + icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0); + SKB_DR_SET(reason, IP_INHDR); +drop: + kfree_skb_reason(skb, reason); + return NET_RX_DROP; +} |