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 <net/ip.h>
15 #include <bpf/bpf_helpers.h>
16 
17 #define DEFAULT_PKTGEN_UDP_PORT 9
18 
19 /* copy of 'struct ethhdr' without __packed */
20 struct eth_hdr {
21 	unsigned char   h_dest[ETH_ALEN];
22 	unsigned char   h_source[ETH_ALEN];
23 	unsigned short  h_proto;
24 };
25 
26 SEC("simple")
handle_ingress(struct __sk_buff * skb)27 int handle_ingress(struct __sk_buff *skb)
28 {
29 	void *data = (void *)(long)skb->data;
30 	struct eth_hdr *eth = data;
31 	struct iphdr *iph = data + sizeof(*eth);
32 	struct udphdr *udp = data + sizeof(*eth) + sizeof(*iph);
33 	void *data_end = (void *)(long)skb->data_end;
34 
35 	/* single length check */
36 	if (data + sizeof(*eth) + sizeof(*iph) + sizeof(*udp) > data_end)
37 		return 0;
38 
39 	if (eth->h_proto != htons(ETH_P_IP))
40 		return 0;
41 	if (iph->protocol != IPPROTO_UDP || iph->ihl != 5)
42 		return 0;
43 	if (ip_is_fragment(iph))
44 		return 0;
45 	if (udp->dest == htons(DEFAULT_PKTGEN_UDP_PORT))
46 		return TC_ACT_SHOT;
47 	return 0;
48 }
49 char _license[] SEC("license") = "GPL";
50