Control: harden socket against malformed data and buffer overflows

- immediate close on bad size/type/payload
- recv_len guard to prevent overflow
- unknown commands now close without response

src/control_server.c

@@ -528,8 +528,11 @@ static void client_read_callback(socket_t fd, void* arg) {
     }
 
     client->recv_len += received;
-
-    /* Process messages */
+    if (client->recv_len > ETCPMON_MAX_MSG_SIZE) {
+        DEBUG_ERROR(DEBUG_CATEGORY_CONTROL, "Control recv buffer overflow");
+        if (server) close_client(server, client);
+        return;
+    }
     if (server) {
         handle_client_data(server, client);
     }
@@ -601,6 +604,17 @@ static void handle_client_data(struct control_server* server, struct control_cli
     while (client->recv_len >= sizeof(struct etcpmon_msg_header)) {
         struct etcpmon_msg_header* hdr = (struct etcpmon_msg_header*)client->recv_buffer;
         
+        if (hdr->size == 0 || hdr->size > ETCPMON_MAX_MSG_SIZE) {
+            DEBUG_ERROR(DEBUG_CATEGORY_CONTROL, "Invalid message size from client: %u", hdr->size);
+            close_client(server, client);
+            return;
+        }
+        if (hdr->type < ETCPMON_CMD_LIST_CONN || hdr->type > ETCPMON_CMD_DISCONNECT) {
+            DEBUG_ERROR(DEBUG_CATEGORY_CONTROL, "Invalid command type from client: 0x%02X", hdr->type);
+            close_client(server, client);
+            return;
+        }
+        
         /* Validate header */
         if (etcpmon_validate_header(hdr) != 0) {
             if (server->log_file) {
@@ -646,6 +660,10 @@ static void handle_client_data(struct control_server* server, struct control_cli
                     }
                     DEBUG_INFO(DEBUG_CATEGORY_CONTROL, "Client selected connection: %016llX",
                                (unsigned long long)cmd->peer_node_id);
+                } else {
+                    DEBUG_ERROR(DEBUG_CATEGORY_CONTROL, "Bad SELECT_CONN payload size %u", payload_size);
+                    close_client(server, client);
+                    return;
                 }
                 break;
 
@@ -668,14 +686,9 @@ static void handle_client_data(struct control_server* server, struct control_cli
                 return;
 
             default:
-                if (server->log_file) {
-                    fprintf(server->log_file, "%llu: [ERROR] Unknown command from client: 0x%02X\n",
-                           (unsigned long long)get_timestamp_ms(), hdr->type);
-                    fflush(server->log_file);
-                }
-                DEBUG_WARN(DEBUG_CATEGORY_CONTROL, "Unknown command from client: 0x%02X", hdr->type);
-                send_error(client, ETCPMON_ERR_INVALID_CMD, "Unknown command", req_seq);
-                break;
+                DEBUG_ERROR(DEBUG_CATEGORY_CONTROL, "Unknown command from client: 0x%02X", hdr->type);
+                close_client(server, client);
+                return;
         }
         
         /* Remove processed message from buffer */