root/samples/bpf/parse_ldabs.c

DEFINITIONS

1. ip_is_fragment
2. SEC

   1 /* Copyright (c) 2016 Facebook
   2  *
   3  * This program is free software; you can redistribute it and/or
   4  * modify it under the terms of version 2 of the GNU General Public
   5  * License as published by the Free Software Foundation.
   6  */
   7 #define KBUILD_MODNAME "foo"
   8 #include <linux/ip.h>
   9 #include <linux/ipv6.h>
  10 #include <linux/in.h>
  11 #include <linux/tcp.h>
  12 #include <linux/udp.h>
  13 #include <uapi/linux/bpf.h>
  14 #include "bpf_helpers.h"
  15 
  16 #define DEFAULT_PKTGEN_UDP_PORT 9
  17 #define IP_MF                   0x2000
  18 #define IP_OFFSET               0x1FFF
  19 
  20 static inline int ip_is_fragment(struct __sk_buff *ctx, __u64 nhoff)
  21 {
  22         return load_half(ctx, nhoff + offsetof(struct iphdr, frag_off))
  23                 & (IP_MF | IP_OFFSET);
  24 }
  25 
  26 SEC("ldabs")
  27 int handle_ingress(struct __sk_buff *skb)
  28 {
  29         __u64 troff = ETH_HLEN + sizeof(struct iphdr);
  30 
  31         if (load_half(skb, offsetof(struct ethhdr, h_proto)) != ETH_P_IP)
  32                 return 0;
  33         if (load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)) != IPPROTO_UDP ||
  34             load_byte(skb, ETH_HLEN) != 0x45)
  35                 return 0;
  36         if (ip_is_fragment(skb, ETH_HLEN))
  37                 return 0;
  38         if (load_half(skb, troff + offsetof(struct udphdr, dest)) == DEFAULT_PKTGEN_UDP_PORT)
  39                 return TC_ACT_SHOT;
  40         return 0;
  41 }
  42 char _license[] SEC("license") = "GPL";