/* 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 <net/ip.h>
  #include "bpf_helpers.h"
  
  #define DEFAULT_PKTGEN_UDP_PORT 9
  
  /* 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;
  };
  
  SEC("simple")
  int handle_ingress(struct __sk_buff *skb)
  {
  	void *data = (void *)(long)skb->data;
  	struct eth_hdr *eth = data;
  	struct iphdr *iph = data + sizeof(*eth);
  	struct udphdr *udp = data + sizeof(*eth) + sizeof(*iph);
  	void *data_end = (void *)(long)skb->data_end;
  
  	/* single length check */
  	if (data + sizeof(*eth) + sizeof(*iph) + sizeof(*udp) > data_end)
  		return 0;
  
  	if (eth->h_proto != htons(ETH_P_IP))
  		return 0;
  	if (iph->protocol != IPPROTO_UDP || iph->ihl != 5)
  		return 0;
  	if (ip_is_fragment(iph))
  		return 0;
  	if (udp->dest == htons(DEFAULT_PKTGEN_UDP_PORT))
  		return TC_ACT_SHOT;
  	return 0;
  }
  char _license[] SEC("license") = "GPL";