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