XDP Drop udp example

udp.c

#include <linux/bpf.h>
#include <linux/in.h>
#include <linux/if_ether.h>
#include <linux/ip.h>

#define SEC(NAME) __attribute__((section(NAME), used))

SEC("dropper_main")
int dropper(struct xdp_md *ctx) {
  int ipsize = 0;

  void *data = (void *)(long)ctx->data;
  void *data_end = (void *)(long)ctx->data_end;

  struct ethhdr *eth = data;

  ipsize = sizeof(*eth);

  struct iphdr *ip = data + ipsize;
  ipsize += sizeof(struct iphdr);
  if (data + ipsize > data_end) {
    return XDP_PASS;
  }

  if (ip->protocol == IPPROTO_UDP) {
    return XDP_DROP;
  }

  return XDP_PASS;
}

char _license[] SEC("license") = "GPL";