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/bpf_helpers.h>
15 #include "bpf_legacy.h"
16 
17 #define DEFAULT_PKTGEN_UDP_PORT	9
18 #define IP_MF			0x2000
19 #define IP_OFFSET		0x1FFF
20 
ip_is_fragment(struct __sk_buff * ctx,__u64 nhoff)21 static inline int ip_is_fragment(struct __sk_buff *ctx, __u64 nhoff)
22 {
23 	return load_half(ctx, nhoff + offsetof(struct iphdr, frag_off))
24 		& (IP_MF | IP_OFFSET);
25 }
26 
27 SEC("ldabs")
handle_ingress(struct __sk_buff * skb)28 int handle_ingress(struct __sk_buff *skb)
29 {
30 	__u64 troff = ETH_HLEN + sizeof(struct iphdr);
31 
32 	if (load_half(skb, offsetof(struct ethhdr, h_proto)) != ETH_P_IP)
33 		return 0;
34 	if (load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)) != IPPROTO_UDP ||
35 	    load_byte(skb, ETH_HLEN) != 0x45)
36 		return 0;
37 	if (ip_is_fragment(skb, ETH_HLEN))
38 		return 0;
39 	if (load_half(skb, troff + offsetof(struct udphdr, dest)) == DEFAULT_PKTGEN_UDP_PORT)
40 		return TC_ACT_SHOT;
41 	return 0;
42 }
43 char _license[] SEC("license") = "GPL";
44