text: /* 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.
   */
  #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_helpers.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";
  