// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2023 Isovalent */
#include <stdbool.h>
#include <linux/bpf.h>
#include <linux/if_ether.h>
#include <linux/in.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <bpf/bpf_endian.h>
#include <bpf/bpf_helpers.h>
#include <linux/pkt_cls.h>

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

__u64 sk_cookie_seen;
__u64 reuseport_executed;
union {
        struct tcphdr tcp;
        struct udphdr udp;
} headers;

const volatile __u16 dest_port;

struct {
        __uint(type, BPF_MAP_TYPE_SOCKMAP);
        __uint(max_entries, 1);
        __type(key, __u32);
        __type(value, __u64);
} sk_map SEC(".maps");

SEC("sk_reuseport")
int reuse_accept(struct sk_reuseport_md *ctx)
{
        reuseport_executed++;

        if (ctx->ip_protocol == IPPROTO_TCP) {
                if (ctx->data + sizeof(headers.tcp) > ctx->data_end)
                        return SK_DROP;

                if (__builtin_memcmp(&headers.tcp, ctx->data, sizeof(headers.tcp)) != 0)
                        return SK_DROP;
        } else if (ctx->ip_protocol == IPPROTO_UDP) {
                if (ctx->data + sizeof(headers.udp) > ctx->data_end)
                        return SK_DROP;

                if (__builtin_memcmp(&headers.udp, ctx->data, sizeof(headers.udp)) != 0)
                        return SK_DROP;
        } else {
                return SK_DROP;
        }

        sk_cookie_seen = bpf_get_socket_cookie(ctx->sk);
        return SK_PASS;
}

SEC("sk_reuseport")
int reuse_drop(struct sk_reuseport_md *ctx)
{
        reuseport_executed++;
        sk_cookie_seen = 0;
        return SK_DROP;
}

static int
assign_sk(struct __sk_buff *skb)
{
        int zero = 0, ret = 0;
        struct bpf_sock *sk;

        sk = bpf_map_lookup_elem(&sk_map, &zero);
        if (!sk)
                return TC_ACT_SHOT;
        ret = bpf_sk_assign(skb, sk, 0);
        bpf_sk_release(sk);
        return ret ? TC_ACT_SHOT : TC_ACT_OK;
}

static bool
maybe_assign_tcp(struct __sk_buff *skb, struct tcphdr *th)
{
        if (th + 1 > (void *)(long)(skb->data_end))
                return TC_ACT_SHOT;

        if (!th->syn || th->ack || th->dest != bpf_htons(dest_port))
                return TC_ACT_OK;

        __builtin_memcpy(&headers.tcp, th, sizeof(headers.tcp));
        return assign_sk(skb);
}

static bool
maybe_assign_udp(struct __sk_buff *skb, struct udphdr *uh)
{
        if (uh + 1 > (void *)(long)(skb->data_end))
                return TC_ACT_SHOT;

        if (uh->dest != bpf_htons(dest_port))
                return TC_ACT_OK;

        __builtin_memcpy(&headers.udp, uh, sizeof(headers.udp));
        return assign_sk(skb);
}

SEC("tc")
int tc_main(struct __sk_buff *skb)
{
        void *data_end = (void *)(long)skb->data_end;
        void *data = (void *)(long)skb->data;
        struct ethhdr *eth;

        eth = (struct ethhdr *)(data);
        if (eth + 1 > data_end)
                return TC_ACT_SHOT;

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

                if (iph + 1 > data_end)
                        return TC_ACT_SHOT;

                if (iph->protocol == IPPROTO_TCP)
                        return maybe_assign_tcp(skb, (struct tcphdr *)(iph + 1));
                else if (iph->protocol == IPPROTO_UDP)
                        return maybe_assign_udp(skb, (struct udphdr *)(iph + 1));
                else
                        return TC_ACT_SHOT;
        } else {
                struct ipv6hdr *ip6h = (struct ipv6hdr *)(data + sizeof(*eth));

                if (ip6h + 1 > data_end)
                        return TC_ACT_SHOT;

                if (ip6h->nexthdr == IPPROTO_TCP)
                        return maybe_assign_tcp(skb, (struct tcphdr *)(ip6h + 1));
                else if (ip6h->nexthdr == IPPROTO_UDP)
                        return maybe_assign_udp(skb, (struct udphdr *)(ip6h + 1));
                else
                        return TC_ACT_SHOT;
        }
}