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#include <linux/bpf.h>
#include <linux/if_ether.h>
#include <linux/in.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/udp.h>
#include <stdint.h>
/* IP flags. */
#define IP_CE 0x8000 /* Flag: "Congestion" */
#define IP_DF 0x4000 /* Flag: "Don't Fragment" */
#define IP_MF 0x2000 /* Flag: "More Fragments" */
#define IP_OFFSET 0x1FFF /* "Fragment Offset" part */
#define SEC(NAME) __attribute__((section(NAME), used))
#define htons(x) ((__be16)___constant_swab16((x)))
#define htonl(x) ((__be32)___constant_swab32((x)))
struct vlan_hdr {
__be16 h_vlan_TCI;
__be16 h_vlan_encapsulated_proto;
};
SEC("prog")
int xdp_drop(struct xdp_md *ctx) {
void *data_end = (void *)(long)ctx->data_end;
void *data = (void *)(long)ctx->data;
struct ethhdr *eth = data;
uint64_t nh_off = sizeof(*eth);
if (data + nh_off > data_end) {
return XDP_PASS;
}
uint16_t h_proto = eth->h_proto;
int i;
/* Handle double VLAN tagged packet. See https://en.wikipedia.org/wiki/IEEE_802.1ad */
for (i = 0; i < 2; i++) {
if (h_proto == htons(ETH_P_8021Q) || h_proto == htons(ETH_P_8021AD)) {
struct vlan_hdr *vhdr;
vhdr = data + nh_off;
nh_off += sizeof(struct vlan_hdr);
if (data + nh_off > data_end) {
return XDP_PASS;
}
h_proto = vhdr->h_vlan_encapsulated_proto;
}
}
if (h_proto == htons(ETH_P_IP)) {
struct iphdr *iph = data + nh_off;
struct udphdr *udph = data + nh_off + sizeof(struct iphdr);
uint32_t hostid = iph->daddr >> 24;
if (udph + 1 > (struct udphdr *)data_end) {
return XDP_PASS;
}
if (hostid == 0 || hostid == 255) {
return XDP_DROP;
}
if (iph->frag_off & htons(IP_MF | IP_OFFSET)) {
return XDP_DROP;
}
if (iph->protocol == IPPROTO_UDP) {
__be16 dport = htons(udph->dest);
__be16 sport = htons(udph->source);
if (dport == 53 || sport == 53) {
return XDP_DROP;
}
}
} else if (h_proto == htons(ETH_P_IPV6)) {
struct ipv6hdr *ip6h = data + nh_off;
struct udphdr *udph = data + nh_off + sizeof(struct ipv6hdr);
if (udph + 1 > (struct udphdr *)data_end) {
return XDP_PASS;
}
if (ip6h->nexthdr == IPPROTO_UDP) {
__be16 dport = htons(udph->dest);
__be16 sport = htons(udph->source);
if (dport == 53 || sport == 53) {
return XDP_DROP;
}
}
}
return XDP_PASS;
}
char _license[] SEC("license") = "GPL";
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