1 files changed, 127 insertions, 0 deletions
diff --git a/xdp_udp_handler.c b/xdp_udp_handler.c
new file mode 100644
index 0000000..930667f
--- /dev/null
+++ b/xdp_udp_handler.c
@@ -0,0 +1,127 @@
+#include <linux/bpf.h>
+#include <linux/in.h>
+
+#include <bpf/bpf_helpers.h>
+
+#include "xdp_checksum.h"
+#include "xdp_manip.h"
+#include "xdp_parser.h"
+
+#ifdef XDP_DEBUG
+#define dbg_bpf_printk(fmt, args...) bpf_printk(fmt, ##args)
+#else
+#define dbg_bpf_printk(fmt, args...)
+#endif
+
+#include "common.h"
+
+SEC("xdp")
+int xdp_udp_handler(struct xdp_md *ctx) {
+  void *data_end = (void *)(long)ctx->data_end;
+  void *data = (void *)(long)ctx->data;
+  __u32 action = XDP_PASS; /* Default action */
+  struct hdr_cursor nh = {.pos = data};
+  int nh_type;
+  struct ethhdr *ethhdr;
+  struct iphdr *iphdr = NULL;
+  struct ipv6hdr *ip6hdr = NULL;
+  struct udphdr *udphdr;
+  static const __u8 payload_request[] = {PAYLOAD_REQUEST};
+  static const __u32 payload_request_size = sizeof(payload_request);
+  static const __u8 payload_response[] = {PAYLOAD_RESPONSE};
+  __u32 payload_size;
+
+  nh_type = parse_ethhdr(&nh, data_end, &ethhdr);
+
+  switch (__constant_ntohs(nh_type)) {
+  case ETH_P_IP:
+    nh_type = parse_iphdr(&nh, data_end, &iphdr);
+    break;
+  case ETH_P_IPV6:
+    nh_type = parse_ip6hdr(&nh, data_end, &ip6hdr);
+    break;
+  default:
+    goto out;
+  }
+
+  if (nh_type != IPPROTO_UDP) {
+    goto out;
+  }
+  if (parse_udphdr(&nh, data_end, &udphdr) < 0) {
+    action = XDP_ABORTED;
+    goto out;
+  }
+  if (udphdr->dest != __constant_htons(UDP_PORT)) {
+    goto out;
+  }
+
+  payload_size = (__u8 *)data_end - (__u8 *)nh.pos;
+  if (payload_size < payload_request_size) {
+    goto out;
+  }
+
+  if (nh.pos_u8 + payload_request_size + 1 > (__u8 *)data_end) {
+    goto out;
+  }
+  if (__builtin_memcmp(nh.pos_u8, payload_request, sizeof(payload_request)) !=
+      0) {
+    goto out;
+  }
+
+  dbg_bpf_printk("Received UDP Ping Request #%u with size %u", nh.pos_u8[11],
+                 payload_size);
+
+  /* Shrink UDP packet for Ping Reply */
+  if (bpf_xdp_adjust_tail(ctx, payload_request_size - payload_size) != 0) {
+    return XDP_ABORTED;
+  }
+
+  /* Set data pointers (may not be valid anymore) */
+  data = (void *)(long)ctx->data;
+  data_end = (void *)(long)ctx->data_end;
+  nh.pos = data;
+
+  if (parse_ethhdr(&nh, data_end, &ethhdr) < 0) {
+    action = XDP_ABORTED;
+    goto out;
+  }
+
+  payload_size -= 4;
+
+  if (iphdr != NULL) {
+    if (parse_iphdr(&nh, data_end, &iphdr) < 0) {
+      action = XDP_ABORTED;
+      goto out;
+    }
+    if (parse_udphdr(&nh, data_end, &udphdr) < 0) {
+      action = XDP_ABORTED;
+      goto out;
+    }
+    swap_eth_addr(ethhdr);
+    udphdr->len = __constant_htons(payload_size + sizeof(*udphdr));
+    iphdr->tot_len =
+        __constant_htons(iphdr->ihl * 4 + payload_size + sizeof(*udphdr));
+    swap_ip4_addr(iphdr);
+    iphdr->check = ip_checksum(iphdr);
+    if (nh.pos_u8 + sizeof(payload_response) > (__u8 *)data_end) {
+      action = XDP_ABORTED;
+      goto out;
+    }
+    __builtin_memcpy(nh.pos_u8, payload_response, sizeof(payload_response));
+    swap_udp_port(udphdr);
+    udphdr->check = udp_checksum(iphdr, udphdr, data_end);
+  } else if (ip6hdr != NULL) {
+    parse_ip6hdr(&nh, data_end, &ip6hdr);
+    goto out; // TODO: Implement!
+  } else {
+    action = XDP_ABORTED;
+    goto out;
+  }
+
+  action = XDP_TX;
+out:
+  return action;
+}
+
+char _license[] SEC("license") =
+    "GPL"; // Please keep this to prevent tainting kernel