/* Copyright (c) 2017 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.
 */
#include <stddef.h>
#include <stdbool.h>
#include <string.h>
#include <linux/pkt_cls.h>
#include <linux/bpf.h>
#include <linux/in.h>
#include <linux/if_ether.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/icmp.h>
#include <linux/icmpv6.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <bpf/bpf_helpers.h>
#include "test_iptunnel_common.h"
#include <bpf/bpf_endian.h>

static inline __u32 rol32(__u32 word, unsigned int shift)
{
        return (word << shift) | (word >> ((-shift) & 31));
}

/* copy paste of jhash from kernel sources to make sure llvm
 * can compile it into valid sequence of bpf instructions
 */
#define __jhash_mix(a, b, c)                    \
{                                               \
        a -= c;  a ^= rol32(c, 4);  c += b;     \
        b -= a;  b ^= rol32(a, 6);  a += c;     \
        c -= b;  c ^= rol32(b, 8);  b += a;     \
        a -= c;  a ^= rol32(c, 16); c += b;     \
        b -= a;  b ^= rol32(a, 19); a += c;     \
        c -= b;  c ^= rol32(b, 4);  b += a;     \
}

#define __jhash_final(a, b, c)                  \
{                                               \
        c ^= b; c -= rol32(b, 14);              \
        a ^= c; a -= rol32(c, 11);              \
        b ^= a; b -= rol32(a, 25);              \
        c ^= b; c -= rol32(b, 16);              \
        a ^= c; a -= rol32(c, 4);               \
        b ^= a; b -= rol32(a, 14);              \
        c ^= b; c -= rol32(b, 24);              \
}

#define JHASH_INITVAL           0xdeadbeef

typedef unsigned int u32;

static inline u32 jhash(const void *key, u32 length, u32 initval)
{
        u32 a, b, c;
        const unsigned char *k = key;

        a = b = c = JHASH_INITVAL + length + initval;

        while (length > 12) {
                a += *(u32 *)(k);
                b += *(u32 *)(k + 4);
                c += *(u32 *)(k + 8);
                __jhash_mix(a, b, c);
                length -= 12;
                k += 12;
        }
        switch (length) {
        case 12: c += (u32)k[11]<<24;
        case 11: c += (u32)k[10]<<16;
        case 10: c += (u32)k[9]<<8;
        case 9:  c += k[8];
        case 8:  b += (u32)k[7]<<24;
        case 7:  b += (u32)k[6]<<16;
        case 6:  b += (u32)k[5]<<8;
        case 5:  b += k[4];
        case 4:  a += (u32)k[3]<<24;
        case 3:  a += (u32)k[2]<<16;
        case 2:  a += (u32)k[1]<<8;
        case 1:  a += k[0];
                 __jhash_final(a, b, c);
        case 0: /* Nothing left to add */
                break;
        }

        return c;
}

static inline u32 __jhash_nwords(u32 a, u32 b, u32 c, u32 initval)
{
        a += initval;
        b += initval;
        c += initval;
        __jhash_final(a, b, c);
        return c;
}

static inline u32 jhash_2words(u32 a, u32 b, u32 initval)
{
        return __jhash_nwords(a, b, 0, initval + JHASH_INITVAL + (2 << 2));
}

#define PCKT_FRAGMENTED 65343
#define IPV4_HDR_LEN_NO_OPT 20
#define IPV4_PLUS_ICMP_HDR 28
#define IPV6_PLUS_ICMP_HDR 48
#define RING_SIZE 2
#define MAX_VIPS 12
#define MAX_REALS 5
#define CTL_MAP_SIZE 16
#define CH_RINGS_SIZE (MAX_VIPS * RING_SIZE)
#define F_IPV6 (1 << 0)
#define F_HASH_NO_SRC_PORT (1 << 0)
#define F_ICMP (1 << 0)
#define F_SYN_SET (1 << 1)

struct packet_description {
        union {
                __be32 src;
                __be32 srcv6[4];
        };
        union {
                __be32 dst;
                __be32 dstv6[4];
        };
        union {
                __u32 ports;
                __u16 port16[2];
        };
        __u8 proto;
        __u8 flags;
};

struct ctl_value {
        union {
                __u64 value;
                __u32 ifindex;
                __u8 mac[6];
        };
};

struct vip_meta {
        __u32 flags;
        __u32 vip_num;
};

struct real_definition {
        union {
                __be32 dst;
                __be32 dstv6[4];
        };
        __u8 flags;
};

struct vip_stats {
        __u64 bytes;
        __u64 pkts;
};

struct eth_hdr {
        unsigned char eth_dest[ETH_ALEN];
        unsigned char eth_source[ETH_ALEN];
        unsigned short eth_proto;
};

struct {
        __uint(type, BPF_MAP_TYPE_HASH);
        __uint(max_entries, MAX_VIPS);
        __type(key, struct vip);
        __type(value, struct vip_meta);
} vip_map SEC(".maps");

struct {
        __uint(type, BPF_MAP_TYPE_ARRAY);
        __uint(max_entries, CH_RINGS_SIZE);
        __type(key, __u32);
        __type(value, __u32);
} ch_rings SEC(".maps");

struct {
        __uint(type, BPF_MAP_TYPE_ARRAY);
        __uint(max_entries, MAX_REALS);
        __type(key, __u32);
        __type(value, struct real_definition);
} reals SEC(".maps");

struct {
        __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
        __uint(max_entries, MAX_VIPS);
        __type(key, __u32);
        __type(value, struct vip_stats);
} stats SEC(".maps");

struct {
        __uint(type, BPF_MAP_TYPE_ARRAY);
        __uint(max_entries, CTL_MAP_SIZE);
        __type(key, __u32);
        __type(value, struct ctl_value);
} ctl_array SEC(".maps");

static __always_inline __u32 get_packet_hash(struct packet_description *pckt,
                                             bool ipv6)
{
        if (ipv6)
                return jhash_2words(jhash(pckt->srcv6, 16, MAX_VIPS),
                                    pckt->ports, CH_RINGS_SIZE);
        else
                return jhash_2words(pckt->src, pckt->ports, CH_RINGS_SIZE);
}

static __always_inline bool get_packet_dst(struct real_definition **real,
                                           struct packet_description *pckt,
                                           struct vip_meta *vip_info,
                                           bool is_ipv6)
{
        __u32 hash = get_packet_hash(pckt, is_ipv6) % RING_SIZE;
        __u32 key = RING_SIZE * vip_info->vip_num + hash;
        __u32 *real_pos;

        real_pos = bpf_map_lookup_elem(&ch_rings, &key);
        if (!real_pos)
                return false;
        key = *real_pos;
        *real = bpf_map_lookup_elem(&reals, &key);
        if (!(*real))
                return false;
        return true;
}

static __always_inline int parse_icmpv6(void *data, void *data_end, __u64 off,
                                        struct packet_description *pckt)
{
        struct icmp6hdr *icmp_hdr;
        struct ipv6hdr *ip6h;

        icmp_hdr = data + off;
        if (icmp_hdr + 1 > data_end)
                return TC_ACT_SHOT;
        if (icmp_hdr->icmp6_type != ICMPV6_PKT_TOOBIG)
                return TC_ACT_OK;
        off += sizeof(struct icmp6hdr);
        ip6h = data + off;
        if (ip6h + 1 > data_end)
                return TC_ACT_SHOT;
        pckt->proto = ip6h->nexthdr;
        pckt->flags |= F_ICMP;
        memcpy(pckt->srcv6, ip6h->daddr.s6_addr32, 16);
        memcpy(pckt->dstv6, ip6h->saddr.s6_addr32, 16);
        return TC_ACT_UNSPEC;
}

static __always_inline int parse_icmp(void *data, void *data_end, __u64 off,
                                      struct packet_description *pckt)
{
        struct icmphdr *icmp_hdr;
        struct iphdr *iph;

        icmp_hdr = data + off;
        if (icmp_hdr + 1 > data_end)
                return TC_ACT_SHOT;
        if (icmp_hdr->type != ICMP_DEST_UNREACH ||
            icmp_hdr->code != ICMP_FRAG_NEEDED)
                return TC_ACT_OK;
        off += sizeof(struct icmphdr);
        iph = data + off;
        if (iph + 1 > data_end)
                return TC_ACT_SHOT;
        if (iph->ihl != 5)
                return TC_ACT_SHOT;
        pckt->proto = iph->protocol;
        pckt->flags |= F_ICMP;
        pckt->src = iph->daddr;
        pckt->dst = iph->saddr;
        return TC_ACT_UNSPEC;
}

static __always_inline bool parse_udp(void *data, __u64 off, void *data_end,
                                      struct packet_description *pckt)
{
        struct udphdr *udp;
        udp = data + off;

        if (udp + 1 > data_end)
                return false;

        if (!(pckt->flags & F_ICMP)) {
                pckt->port16[0] = udp->source;
                pckt->port16[1] = udp->dest;
        } else {
                pckt->port16[0] = udp->dest;
                pckt->port16[1] = udp->source;
        }
        return true;
}

static __always_inline bool parse_tcp(void *data, __u64 off, void *data_end,
                                      struct packet_description *pckt)
{
        struct tcphdr *tcp;

        tcp = data + off;
        if (tcp + 1 > data_end)
                return false;

        if (tcp->syn)
                pckt->flags |= F_SYN_SET;

        if (!(pckt->flags & F_ICMP)) {
                pckt->port16[0] = tcp->source;
                pckt->port16[1] = tcp->dest;
        } else {
                pckt->port16[0] = tcp->dest;
                pckt->port16[1] = tcp->source;
        }
        return true;
}

static __always_inline int process_packet(void *data, __u64 off, void *data_end,
                                          bool is_ipv6, struct __sk_buff *skb)
{
        void *pkt_start = (void *)(long)skb->data;
        struct packet_description pckt = {};
        struct eth_hdr *eth = pkt_start;
        struct bpf_tunnel_key tkey = {};
        struct vip_stats *data_stats;
        struct real_definition *dst;
        struct vip_meta *vip_info;
        struct ctl_value *cval;
        __u32 v4_intf_pos = 1;
        __u32 v6_intf_pos = 2;
        struct ipv6hdr *ip6h;
        struct vip vip = {};
        struct iphdr *iph;
        int tun_flag = 0;
        __u16 pkt_bytes;
        __u64 iph_len;
        __u32 ifindex;
        __u8 protocol;
        __u32 vip_num;
        int action;

        tkey.tunnel_ttl = 64;
        if (is_ipv6) {
                ip6h = data + off;
                if (ip6h + 1 > data_end)
                        return TC_ACT_SHOT;

                iph_len = sizeof(struct ipv6hdr);
                protocol = ip6h->nexthdr;
                pckt.proto = protocol;
                pkt_bytes = bpf_ntohs(ip6h->payload_len);
                off += iph_len;
                if (protocol == IPPROTO_FRAGMENT) {
                        return TC_ACT_SHOT;
                } else if (protocol == IPPROTO_ICMPV6) {
                        action = parse_icmpv6(data, data_end, off, &pckt);
                        if (action >= 0)
                                return action;
                        off += IPV6_PLUS_ICMP_HDR;
                } else {
                        memcpy(pckt.srcv6, ip6h->saddr.s6_addr32, 16);
                        memcpy(pckt.dstv6, ip6h->daddr.s6_addr32, 16);
                }
        } else {
                iph = data + off;
                if (iph + 1 > data_end)
                        return TC_ACT_SHOT;
                if (iph->ihl != 5)
                        return TC_ACT_SHOT;

                protocol = iph->protocol;
                pckt.proto = protocol;
                pkt_bytes = bpf_ntohs(iph->tot_len);
                off += IPV4_HDR_LEN_NO_OPT;

                if (iph->frag_off & PCKT_FRAGMENTED)
                        return TC_ACT_SHOT;
                if (protocol == IPPROTO_ICMP) {
                        action = parse_icmp(data, data_end, off, &pckt);
                        if (action >= 0)
                                return action;
                        off += IPV4_PLUS_ICMP_HDR;
                } else {
                        pckt.src = iph->saddr;
                        pckt.dst = iph->daddr;
                }
        }
        protocol = pckt.proto;

        if (protocol == IPPROTO_TCP) {
                if (!parse_tcp(data, off, data_end, &pckt))
                        return TC_ACT_SHOT;
        } else if (protocol == IPPROTO_UDP) {
                if (!parse_udp(data, off, data_end, &pckt))
                        return TC_ACT_SHOT;
        } else {
                return TC_ACT_SHOT;
        }

        if (is_ipv6)
                memcpy(vip.daddr.v6, pckt.dstv6, 16);
        else
                vip.daddr.v4 = pckt.dst;

        vip.dport = pckt.port16[1];
        vip.protocol = pckt.proto;
        vip_info = bpf_map_lookup_elem(&vip_map, &vip);
        if (!vip_info) {
                vip.dport = 0;
                vip_info = bpf_map_lookup_elem(&vip_map, &vip);
                if (!vip_info)
                        return TC_ACT_SHOT;
                pckt.port16[1] = 0;
        }

        if (vip_info->flags & F_HASH_NO_SRC_PORT)
                pckt.port16[0] = 0;

        if (!get_packet_dst(&dst, &pckt, vip_info, is_ipv6))
                return TC_ACT_SHOT;

        if (dst->flags & F_IPV6) {
                cval = bpf_map_lookup_elem(&ctl_array, &v6_intf_pos);
                if (!cval)
                        return TC_ACT_SHOT;
                ifindex = cval->ifindex;
                memcpy(tkey.remote_ipv6, dst->dstv6, 16);
                tun_flag = BPF_F_TUNINFO_IPV6;
        } else {
                cval = bpf_map_lookup_elem(&ctl_array, &v4_intf_pos);
                if (!cval)
                        return TC_ACT_SHOT;
                ifindex = cval->ifindex;
                tkey.remote_ipv4 = dst->dst;
        }
        vip_num = vip_info->vip_num;
        data_stats = bpf_map_lookup_elem(&stats, &vip_num);
        if (!data_stats)
                return TC_ACT_SHOT;
        data_stats->pkts++;
        data_stats->bytes += pkt_bytes;
        bpf_skb_set_tunnel_key(skb, &tkey, sizeof(tkey), tun_flag);
        *(u32 *)eth->eth_dest = tkey.remote_ipv4;
        return bpf_redirect(ifindex, 0);
}

SEC("tc")
int balancer_ingress(struct __sk_buff *ctx)
{
        void *data_end = (void *)(long)ctx->data_end;
        void *data = (void *)(long)ctx->data;
        struct eth_hdr *eth = data;
        __u32 eth_proto;
        __u32 nh_off;

        nh_off = sizeof(struct eth_hdr);
        if (data + nh_off > data_end)
                return TC_ACT_SHOT;
        eth_proto = eth->eth_proto;
        if (eth_proto == bpf_htons(ETH_P_IP))
                return process_packet(data, nh_off, data_end, false, ctx);
        else if (eth_proto == bpf_htons(ETH_P_IPV6))
                return process_packet(data, nh_off, data_end, true, ctx);
        else
                return TC_ACT_SHOT;
}
char _license[] SEC("license") = "GPL";