commit ba3cb97357e24cadc9254157a62f48f82672fc12
Author: norohind <60548839+norohind@users.noreply.github.com>
Date:   Thu Feb 13 23:20:19 2025 +0100

    init

diff --git a/bind.c b/bind.c
new file mode 100644
index 0000000..8578d4e
--- /dev/null
+++ b/bind.c
@@ -0,0 +1,88 @@
+#define _GNU_SOURCE
+#include <dlfcn.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+#include <unistd.h>
+#include <net/if.h> // For if_nametoindex
+
+// Build with: gcc -shared -fPIC bind.c -o libbind.so -ldl
+// Typedef for the original `bind()` function
+typedef int (*pfn_bind_t)(int sockfd, const struct sockaddr *addr, socklen_t addrlen);
+
+// Hardcoded adapter name for the IPv6 link-local address
+#define HARDCODED_ADAPTER "enp5s0f3u1"
+
+// Our custom `bind()` function
+int bind(int sockfd, const struct sockaddr *addr, socklen_t addrlen) {
+    // Get the original `bind()` function
+    pfn_bind_t original_bind = (pfn_bind_t)dlsym(RTLD_NEXT, "bind");
+
+    // Get environment variables
+    const char *bind_addr_env = getenv("BIND_ADDR");
+    const char *bind_addr6_env = getenv("BIND_ADDR6");
+
+    // Handle IPv4 binding
+    if (addr->sa_family == AF_INET) {
+        if (!bind_addr_env) {
+            fprintf(stderr, "bind(): BIND_ADDR not set, skipping IPv4 bind\n");
+            return 0; // Simulate success
+        }
+
+        struct sockaddr_in new_addr;
+        memcpy(&new_addr, addr, sizeof(new_addr)); // Copy the original address
+
+        // Replace the IP address
+        if (inet_pton(AF_INET, bind_addr_env, &new_addr.sin_addr) != 1) {
+            fprintf(stderr, "Invalid BIND_ADDR: %s\n", bind_addr_env);
+            return 0; // Simulate success even if the address is invalid
+        }
+
+        // Log the modification
+        char original_ip[INET_ADDRSTRLEN];
+        inet_ntop(AF_INET, &((struct sockaddr_in *)addr)->sin_addr, original_ip, INET_ADDRSTRLEN);
+        fprintf(stderr, "bind(): Replacing IPv4 address %s with %s\n", original_ip, bind_addr_env);
+
+        // Call the original `bind()` with the modified address
+        return original_bind(sockfd, (struct sockaddr *)&new_addr, addrlen);
+    }
+
+    // Handle IPv6 binding
+    if (addr->sa_family == AF_INET6) {
+        if (!bind_addr6_env) {
+            fprintf(stderr, "bind(): BIND_ADDR6 not set, skipping IPv6 bind\n");
+            return 0; // Simulate success
+        }
+
+        struct sockaddr_in6 new_addr6;
+        memcpy(&new_addr6, addr, sizeof(new_addr6)); // Copy the original address
+
+        // Replace the IP address
+        if (inet_pton(AF_INET6, bind_addr6_env, &new_addr6.sin6_addr) != 1) {
+            fprintf(stderr, "Invalid BIND_ADDR6: %s\n", bind_addr6_env);
+            return 0; // Simulate success even if the address is invalid
+        }
+
+        // Set the scope ID using the hardcoded adapter name
+        new_addr6.sin6_scope_id = if_nametoindex(HARDCODED_ADAPTER);
+        if (new_addr6.sin6_scope_id == 0) {
+            fprintf(stderr, "bind(): Failed to get scope ID for adapter %s\n", HARDCODED_ADAPTER);
+            return 0; // Simulate success even if scope ID can't be set
+        }
+
+        // Log the modification
+        char original_ip6[INET6_ADDRSTRLEN];
+        inet_ntop(AF_INET6, &((struct sockaddr_in6 *)addr)->sin6_addr, original_ip6, INET6_ADDRSTRLEN);
+        fprintf(stderr, "bind(): Replacing IPv6 address %s with %s and scope ID %d\n",
+                original_ip6, bind_addr6_env, new_addr6.sin6_scope_id);
+
+        // Call the original `bind()` with the modified address
+        return original_bind(sockfd, (struct sockaddr *)&new_addr6, addrlen);
+    }
+
+    // If it's neither IPv4 nor IPv6, call the original `bind()` as-is
+    return original_bind(sockfd, addr, addrlen);
+}