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 
13 static 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 
24 out:
25 	return ip;
26 }
27 
28 SEC("classifier/cls")
29 int 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;
50 out:
51 	return -1;
52 }
53 char _license[] SEC("license") = "GPL";
54