/* Copyright (c) 2016 Facebook
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 */
#define KBUILD_MODNAME "foo"
#include <uapi/linux/bpf.h>
#include <uapi/linux/if_ether.h>
#include <uapi/linux/if_packet.h>
#include <uapi/linux/ip.h>
#include <uapi/linux/ipv6.h>
#include <uapi/linux/in.h>
#include <uapi/linux/tcp.h>
#include <uapi/linux/filter.h>
#include <uapi/linux/pkt_cls.h>
#include <net/ipv6.h>
#include <bpf/bpf_helpers.h>

#define _htonl __builtin_bswap32

#define PIN_GLOBAL_NS           2
struct bpf_elf_map {
        __u32 type;
        __u32 size_key;
        __u32 size_value;
        __u32 max_elem;
        __u32 flags;
        __u32 id;
        __u32 pinning;
};

/* copy of 'struct ethhdr' without __packed */
struct eth_hdr {
        unsigned char   h_dest[ETH_ALEN];
        unsigned char   h_source[ETH_ALEN];
        unsigned short  h_proto;
};

struct bpf_elf_map SEC("maps") tun_iface = {
        .type = BPF_MAP_TYPE_ARRAY,
        .size_key = sizeof(int),
        .size_value = sizeof(int),
        .pinning = PIN_GLOBAL_NS,
        .max_elem = 1,
};

static __always_inline bool is_vip_addr(__be16 eth_proto, __be32 daddr)
{
        if (eth_proto == htons(ETH_P_IP))
                return (_htonl(0xffffff00) & daddr) == _htonl(0x0a0a0100);
        else if (eth_proto == htons(ETH_P_IPV6))
                return (daddr == _htonl(0x2401face));

        return false;
}

SEC("l2_to_iptun_ingress_forward")
int _l2_to_iptun_ingress_forward(struct __sk_buff *skb)
{
        void *data = (void *)(long)skb->data;
        struct eth_hdr *eth = data;
        void *data_end = (void *)(long)skb->data_end;
        int key = 0, *ifindex;

        if (data + sizeof(*eth) > data_end)
                return TC_ACT_OK;

        ifindex = bpf_map_lookup_elem(&tun_iface, &key);
        if (!ifindex)
                return TC_ACT_OK;

        if (eth->h_proto == htons(ETH_P_IP)) {
                char fmt4[] = "ingress forward to ifindex:%d daddr4:%x\n";
                struct iphdr *iph = data + sizeof(*eth);

                if (data + sizeof(*eth) + sizeof(*iph) > data_end)
                        return TC_ACT_OK;

                if (iph->protocol != IPPROTO_IPIP)
                        return TC_ACT_OK;

                bpf_trace_printk(fmt4, sizeof(fmt4), *ifindex,
                                 _htonl(iph->daddr));
                return bpf_redirect(*ifindex, BPF_F_INGRESS);
        } else if (eth->h_proto == htons(ETH_P_IPV6)) {
                char fmt6[] = "ingress forward to ifindex:%d daddr6:%x::%x\n";
                struct ipv6hdr *ip6h = data + sizeof(*eth);

                if (data + sizeof(*eth) + sizeof(*ip6h) > data_end)
                        return TC_ACT_OK;

                if (ip6h->nexthdr != IPPROTO_IPIP &&
                    ip6h->nexthdr != IPPROTO_IPV6)
                        return TC_ACT_OK;

                bpf_trace_printk(fmt6, sizeof(fmt6), *ifindex,
                                 _htonl(ip6h->daddr.s6_addr32[0]),
                                 _htonl(ip6h->daddr.s6_addr32[3]));
                return bpf_redirect(*ifindex, BPF_F_INGRESS);
        }

        return TC_ACT_OK;
}

SEC("l2_to_iptun_ingress_redirect")
int _l2_to_iptun_ingress_redirect(struct __sk_buff *skb)
{
        struct bpf_tunnel_key tkey = {};
        void *data = (void *)(long)skb->data;
        struct eth_hdr *eth = data;
        void *data_end = (void *)(long)skb->data_end;
        int key = 0, *ifindex;

        if (data + sizeof(*eth) > data_end)
                return TC_ACT_OK;

        ifindex = bpf_map_lookup_elem(&tun_iface, &key);
        if (!ifindex)
                return TC_ACT_OK;

        if (eth->h_proto == htons(ETH_P_IP)) {
                char fmt4[] = "e/ingress redirect daddr4:%x to ifindex:%d\n";
                struct iphdr *iph = data + sizeof(*eth);
                __be32 daddr = iph->daddr;

                if (data + sizeof(*eth) + sizeof(*iph) > data_end)
                        return TC_ACT_OK;

                if (!is_vip_addr(eth->h_proto, daddr))
                        return TC_ACT_OK;

                bpf_trace_printk(fmt4, sizeof(fmt4), _htonl(daddr), *ifindex);
        } else {
                return TC_ACT_OK;
        }

        tkey.tunnel_id = 10000;
        tkey.tunnel_ttl = 64;
        tkey.remote_ipv4 = 0x0a020166; /* 10.2.1.102 */
        bpf_skb_set_tunnel_key(skb, &tkey, sizeof(tkey), 0);
        return bpf_redirect(*ifindex, 0);
}

SEC("l2_to_ip6tun_ingress_redirect")
int _l2_to_ip6tun_ingress_redirect(struct __sk_buff *skb)
{
        struct bpf_tunnel_key tkey = {};
        void *data = (void *)(long)skb->data;
        struct eth_hdr *eth = data;
        void *data_end = (void *)(long)skb->data_end;
        int key = 0, *ifindex;

        if (data + sizeof(*eth) > data_end)
                return TC_ACT_OK;

        ifindex = bpf_map_lookup_elem(&tun_iface, &key);
        if (!ifindex)
                return TC_ACT_OK;

        if (eth->h_proto == htons(ETH_P_IP)) {
                char fmt4[] = "e/ingress redirect daddr4:%x to ifindex:%d\n";
                struct iphdr *iph = data + sizeof(*eth);

                if (data + sizeof(*eth) + sizeof(*iph) > data_end)
                        return TC_ACT_OK;

                if (!is_vip_addr(eth->h_proto, iph->daddr))
                        return TC_ACT_OK;

                bpf_trace_printk(fmt4, sizeof(fmt4), _htonl(iph->daddr),
                                 *ifindex);
        } else if (eth->h_proto == htons(ETH_P_IPV6)) {
                char fmt6[] = "e/ingress redirect daddr6:%x to ifindex:%d\n";
                struct ipv6hdr *ip6h = data + sizeof(*eth);

                if (data + sizeof(*eth) + sizeof(*ip6h) > data_end)
                        return TC_ACT_OK;

                if (!is_vip_addr(eth->h_proto, ip6h->daddr.s6_addr32[0]))
                        return TC_ACT_OK;

                bpf_trace_printk(fmt6, sizeof(fmt6),
                                 _htonl(ip6h->daddr.s6_addr32[0]), *ifindex);
        } else {
                return TC_ACT_OK;
        }

        tkey.tunnel_id = 10000;
        tkey.tunnel_ttl = 64;
        /* 2401:db02:0:0:0:0:0:66 */
        tkey.remote_ipv6[0] = _htonl(0x2401db02);
        tkey.remote_ipv6[1] = 0;
        tkey.remote_ipv6[2] = 0;
        tkey.remote_ipv6[3] = _htonl(0x00000066);
        bpf_skb_set_tunnel_key(skb, &tkey, sizeof(tkey), BPF_F_TUNINFO_IPV6);
        return bpf_redirect(*ifindex, 0);
}

SEC("drop_non_tun_vip")
int _drop_non_tun_vip(struct __sk_buff *skb)
{
        void *data = (void *)(long)skb->data;
        struct eth_hdr *eth = data;
        void *data_end = (void *)(long)skb->data_end;

        if (data + sizeof(*eth) > data_end)
                return TC_ACT_OK;

        if (eth->h_proto == htons(ETH_P_IP)) {
                struct iphdr *iph = data + sizeof(*eth);

                if (data + sizeof(*eth) + sizeof(*iph) > data_end)
                        return TC_ACT_OK;

                if (is_vip_addr(eth->h_proto, iph->daddr))
                        return TC_ACT_SHOT;
        } else if (eth->h_proto == htons(ETH_P_IPV6)) {
                struct ipv6hdr *ip6h = data + sizeof(*eth);

                if (data + sizeof(*eth) + sizeof(*ip6h) > data_end)
                        return TC_ACT_OK;

                if (is_vip_addr(eth->h_proto, ip6h->daddr.s6_addr32[0]))
                        return TC_ACT_SHOT;
        }

        return TC_ACT_OK;
}

char _license[] SEC("license") = "GPL";