Fix build without import C

2026-10-22 21:39:08 +02:00 · 2023-08-01 10:31:03 +02:00
parent 337020bf59
commit 9a418e8dbf
6 changed files with 4 additions and 2 deletions
@@ -0,0 +1,89 @@
+#include <stdbool.h>
+#include <linux/if_ether.h> // ETH_P_IP
+#include <linux/udp.h>
+#include <linux/ip.h>
+#include <netinet/in.h>
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+#define bpf_printk(fmt, ...)                                                   \
+  ({                                                                           \
+    char ____fmt[] = fmt;                                                      \
+    bpf_trace_printk(____fmt, sizeof(____fmt), ##__VA_ARGS__);                 \
+  })
+
+const __u32 map_key_dns_ip = 0;
+const __u32 map_key_dns_port = 1;
+
+struct bpf_map_def SEC("maps") xdp_port_map = {
+	.type = BPF_MAP_TYPE_ARRAY,
+	.key_size = sizeof(__u32),
+	.value_size = sizeof(__u16),
+	.max_entries = 10,
+};
+
+__be32 dns_ip = 0;
+__be16 dns_port = 0;
+
+bool read_port_settings() {
+    __u16 *value;
+    __be32 *ip_value;
+    value = bpf_map_lookup_elem(&xdp_port_map, &map_key_dns_port);
+    if(!value) {
+        return false;
+    }
+
+    dns_port = htons(*value);
+
+    ip_value = bpf_map_lookup_elem(&xdp_port_map, &map_key_dns_ip);
+    if(!ip_value) {
+        return false;
+    }
+    dns_ip = htonl(*ip_value);
+    return true;
+}
+
+SEC("xdp")
+int xdp_dns_port_fwd(struct xdp_md *ctx) {
+    if(dns_port == 0) {
+        if(!read_port_settings()){
+            return XDP_PASS;
+        }
+        bpf_printk("dns port: %d", dns_port);
+        bpf_printk("dns ip: %d", dns_ip);
+    }
+
+	void *data     = (void *)(long)ctx->data;
+	void *data_end = (void *)(long)ctx->data_end;
+	struct ethhdr *eth = data;
+    struct iphdr  *ip   = (data + sizeof(struct ethhdr));
+    struct udphdr *udp = (data + sizeof(struct ethhdr) + sizeof(struct iphdr));
+
+    // return early if not enough data
+    if (data + sizeof(struct ethhdr) + sizeof(struct iphdr) + sizeof(struct udphdr) > data_end){
+        return XDP_PASS;
+    }
+
+    // skip non IPv4 packages
+    if (eth->h_proto != htons(ETH_P_IP)) {
+       return XDP_PASS;
+    }
+
+    if (ip->protocol != IPPROTO_UDP) {
+       return XDP_PASS;
+    }
+
+    // 2130706433 = 127.0.0.1
+    if (ip->daddr != dns_ip) {
+        return XDP_PASS;
+    }
+
+    // skip non dns ports
+    if (udp->source != htons(53)){
+        return XDP_PASS;
+    }
+
+    udp->dest = dns_port;
+	return XDP_PASS;
+}
+char _license[] SEC("license") = "GPL";