1// SPDX-License-Identifier: GPL-2.0
2#ifndef BPF_NO_PRESERVE_ACCESS_INDEX
3#define BPF_NO_PRESERVE_ACCESS_INDEX
4#endif
5#include <vmlinux.h>
6#include <bpf/bpf_core_read.h>
7#include <bpf/bpf_helpers.h>
8
9#define INLINE __always_inline
10
11#define skb_shorter(skb, len) ((void *)(long)(skb)->data + (len) > (void *)(long)skb->data_end)
12
13#define ETH_IPV4_TCP_SIZE (14 + sizeof(struct iphdr) + sizeof(struct tcphdr))
14
15static INLINE struct iphdr *get_iphdr(struct __sk_buff *skb)
16{
17	struct iphdr *ip = NULL;
18	struct ethhdr *eth;
19
20	if (skb_shorter(skb, ETH_IPV4_TCP_SIZE))
21		goto out;
22
23	eth = (void *)(long)skb->data;
24	ip = (void *)(eth + 1);
25
26out:
27	return ip;
28}
29
30SEC("tc")
31int main_prog(struct __sk_buff *skb)
32{
33	struct iphdr *ip = NULL;
34	struct tcphdr *tcp;
35	__u8 proto = 0;
36
37	if (!(ip = get_iphdr(skb)))
38		goto out;
39
40	proto = ip->protocol;
41
42	if (proto != IPPROTO_TCP)
43		goto out;
44
45	tcp = (void*)(ip + 1);
46	if (tcp->dest != 0)
47		goto out;
48	if (!tcp)
49		goto out;
50
51	return tcp->urg_ptr;
52out:
53	return -1;
54}
55char _license[] SEC("license") = "GPL";
56