#include <linux/ip.h>
#include <linux/in.h>
#include <linux/tcp.h>
#include <linux/bpf.h>
#define ETH_ALEN 6
#define ETH_P_IP 0x0008
#define TCP_HDR_LEN 20
#define BLOCKED_TCP_PORT 0x9999
struct eth_hdr {
unsigned char h_dest[ETH_ALEN];
unsigned char h_source[ETH_ALEN];
unsigned short h_proto;
};
#define SEC(NAME) __attribute__((section(NAME), used))
SEC(".classifier")
int handle_ingress(struct __sk_buff *skb)
{
void *data = (void *)(long)skb->data;
void *data_end = (void *)(long)skb->data_end;
struct eth_hdr *eth = data;
struct iphdr *iph = data + sizeof(*eth);
struct tcphdr *tcp = data + sizeof(*eth) + sizeof(*iph);
if (data + sizeof(*eth) + sizeof(*iph) + sizeof(*tcp) > data_end)
return 0;
if (eth->h_proto != ETH_P_IP)
return 0;
if (iph->protocol != IPPROTO_TCP)
return 0;
if (tcp->source == BLOCKED_TCP_PORT || tcp->dest == BLOCKED_TCP_PORT)
return -1;
return 0;
}