1/* Copyright (c) 2017 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#include <stddef.h>
8#include <string.h>
9#include <linux/bpf.h>
10#include <linux/if_ether.h>
11#include <linux/if_packet.h>
12#include <linux/ip.h>
13#include <linux/ipv6.h>
14#include <linux/in.h>
15#include <linux/tcp.h>
16#include <linux/pkt_cls.h>
17#include "bpf_helpers.h"
18#include "bpf_endian.h"
19
20#define barrier() __asm__ __volatile__("": : :"memory")
21int _version SEC("version") = 1;
22
23SEC("test1")
24int process(struct __sk_buff *skb)
25{
26	void *data_end = (void *)(long)skb->data_end;
27	void *data = (void *)(long)skb->data;
28	struct ethhdr *eth = (struct ethhdr *)(data);
29	struct tcphdr *tcp = NULL;
30	__u8 proto = 255;
31	__u64 ihl_len;
32
33	if (eth + 1 > data_end)
34		return TC_ACT_SHOT;
35
36	if (eth->h_proto == bpf_htons(ETH_P_IP)) {
37		struct iphdr *iph = (struct iphdr *)(eth + 1);
38
39		if (iph + 1 > data_end)
40			return TC_ACT_SHOT;
41		ihl_len = iph->ihl * 4;
42		proto = iph->protocol;
43		tcp = (struct tcphdr *)((void *)(iph) + ihl_len);
44	} else if (eth->h_proto == bpf_htons(ETH_P_IPV6)) {
45		struct ipv6hdr *ip6h = (struct ipv6hdr *)(eth + 1);
46
47		if (ip6h + 1 > data_end)
48			return TC_ACT_SHOT;
49		ihl_len = sizeof(*ip6h);
50		proto = ip6h->nexthdr;
51		tcp = (struct tcphdr *)((void *)(ip6h) + ihl_len);
52	}
53
54	if (tcp) {
55		if (((void *)(tcp) + 20) > data_end || proto != 6)
56			return TC_ACT_SHOT;
57		barrier(); /* to force ordering of checks */
58		if (((void *)(tcp) + 18) > data_end)
59			return TC_ACT_SHOT;
60		if (tcp->urg_ptr == 123)
61			return TC_ACT_OK;
62	}
63
64	return TC_ACT_UNSPEC;
65}
66