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// SPDX-License-Identifier: GPL-2.0
#ifndef BPF_NO_PRESERVE_ACCESS_INDEX
#define BPF_NO_PRESERVE_ACCESS_INDEX
#endif
#include <vmlinux.h>
#include <bpf/bpf_core_read.h>
#include <bpf/bpf_helpers.h>
#define INLINE __always_inline
#define skb_shorter(skb, len) ((void *)(long)(skb)->data + (len) > (void *)(long)skb->data_end)
#define ETH_IPV4_TCP_SIZE (14 + sizeof(struct iphdr) + sizeof(struct tcphdr))
static INLINE struct iphdr *get_iphdr(struct __sk_buff *skb)
{
struct iphdr *ip = NULL;
struct ethhdr *eth;
if (skb_shorter(skb, ETH_IPV4_TCP_SIZE))
goto out;
eth = (void *)(long)skb->data;
ip = (void *)(eth + 1);
out:
return ip;
}
SEC("tc")
int main_prog(struct __sk_buff *skb)
{
struct iphdr *ip = NULL;
struct tcphdr *tcp;
__u8 proto = 0;
int urg_ptr;
u32 offset;
if (!(ip = get_iphdr(skb)))
goto out;
proto = ip->protocol;
if (proto != IPPROTO_TCP)
goto out;
tcp = (void*)(ip + 1);
if (tcp->dest != 0)
goto out;
if (!tcp)
goto out;
urg_ptr = tcp->urg_ptr;
/* Checksum validation part */
proto++;
offset = sizeof(struct ethhdr) + offsetof(struct iphdr, protocol);
bpf_skb_store_bytes(skb, offset, &proto, sizeof(proto), BPF_F_RECOMPUTE_CSUM);
return urg_ptr;
out:
return -1;
}
char _license[] SEC("license") = "GPL";
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