mini fix

src/main.c

@@ -7,6 +7,8 @@
 
 #define ETH_HEADER_SIZE 14
 
+#define MAC_SIZE 6
+
 #define ETHER_TYPE_FIELD_OFFSET 12
 
 #define ETHER_TYPE_IPV4 0x0800
@@ -218,7 +220,7 @@ int xdp_drop_prog(struct xdp_md *ctx) {
   // check SYN
   if (tcp_flags & SYN_MASK) {
     bpf_printk("packet is SYN\n");
-    if (mulberry32_at((__u32)time_seed, dst_port) % 3 == 0) {
+    if (/*mulberry32_at((__u32)time_seed, dst_port) % 3 == 0*/1) {
       bpf_printk("DROPING!\n");
       __u16 *src_port_ptr = (__u16 *)(tcp_packet_data + TCP_SRC_PORT_OFFSET);
       const __u16 src_port = bpf_ntohs(*src_port_ptr);
@@ -284,9 +286,6 @@ int xdp_drop_prog(struct xdp_md *ctx) {
               &pseudo_header,
               (const __u8 *)&pseudo_header + sizeof(pseudo_header), tmp_sum);
         } else {
-          if (EtherType != ETHER_TYPE_IPV6) {
-            return XDP_PASS;
-          }
           if (ip_packet_data + IPV6_HEADER_SIZE > data_end) {
             return XDP_PASS;
           }
@@ -319,7 +318,12 @@ int xdp_drop_prog(struct xdp_md *ctx) {
         tcp_checksum = bpf_htons(tcp_checksum_fold(tmp_sum));
       }
       *(__u16 *)(tcp_packet_data + TCP_CHECKSUM_OFFSET) = tcp_checksum;
-
+      { // swap SRC an dst MAC
+        __u8 src_mac[MAC_SIZE];
+        __builtin_memcpy(src_mac, data + MAC_SIZE, MAC_SIZE);
+        __builtin_memcpy((__u8 *)data + MAC_SIZE, data, MAC_SIZE);
+        __builtin_memcpy((__u8 *)data, src_mac, MAC_SIZE);
+      }
       return XDP_TX;
     }
   } else {