/* 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 <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/in.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <uapi/linux/bpf.h>
#include <bpf/bpf_helpers.h>
#include "bpf_legacy.h"

#define DEFAULT_PKTGEN_UDP_PORT 9
#define IP_MF                   0x2000
#define IP_OFFSET               0x1FFF

static inline int ip_is_fragment(struct __sk_buff *ctx, __u64 nhoff)
{
        return load_half(ctx, nhoff + offsetof(struct iphdr, frag_off))
                & (IP_MF | IP_OFFSET);
}

SEC("ldabs")
int handle_ingress(struct __sk_buff *skb)
{
        __u64 troff = ETH_HLEN + sizeof(struct iphdr);

        if (load_half(skb, offsetof(struct ethhdr, h_proto)) != ETH_P_IP)
                return 0;
        if (load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)) != IPPROTO_UDP ||
            load_byte(skb, ETH_HLEN) != 0x45)
                return 0;
        if (ip_is_fragment(skb, ETH_HLEN))
                return 0;
        if (load_half(skb, troff + offsetof(struct udphdr, dest)) == DEFAULT_PKTGEN_UDP_PORT)
                return TC_ACT_SHOT;
        return 0;
}
char _license[] SEC("license") = "GPL";