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
15 static 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
26 out:
27 return ip;
28 }
29
30 SEC("tc")
31 int main_prog(struct __sk_buff *skb)
32 {
33 struct iphdr *ip = NULL;
34 struct tcphdr *tcp;
35 __u8 proto = 0;
36 int urg_ptr;
37 u32 offset;
38
39 if (!(ip = get_iphdr(skb)))
40 goto out;
41
42 proto = ip->protocol;
43
44 if (proto != IPPROTO_TCP)
45 goto out;
46
47 tcp = (void*)(ip + 1);
48 if (tcp->dest != 0)
49 goto out;
50 if (!tcp)
51 goto out;
52
53 urg_ptr = tcp->urg_ptr;
54
55 /* Checksum validation part */
56 proto++;
57 offset = sizeof(struct ethhdr) + offsetof(struct iphdr, protocol);
58 bpf_skb_store_bytes(skb, offset, &proto, sizeof(proto), BPF_F_RECOMPUTE_CSUM);
59
60 return urg_ptr;
61 out:
62 return -1;
63 }
64 char _license[] SEC("license") = "GPL";
65
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