Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Configuration/System/Configuration/ConfigurationFileMap.cs

@@ -0,0 +1,65 @@
+//------------------------------------------------------------------------------
+// <copyright file="ConfigurationFileMap.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>
+//------------------------------------------------------------------------------
+
+using System;
+using System.IO;
+using System.Security.Permissions;
+
+namespace System.Configuration {
+
+    //
+    // Holds the configuration file mapping for
+    // machine.config. It is the base class for
+    // ExeConfigurationFileMap and WebConfigurationFileMap.
+    //
+    public class ConfigurationFileMap : ICloneable {
+        // DevDiv #407902 - This used to be two fields: one containing the filename and the other containing
+        // a Boolean dictating whether a security check needed to take place. Such a pattern wasn't thread-safe
+        // and could be circumvented by malicious callers. Using a single reference field is guaranteed atomic
+        // read and write across all platforms, so the race condition is eliminated.
+        private Func<string> _getFilenameThunk;
+
+        public ConfigurationFileMap() {
+            _getFilenameThunk = GetFilenameFromMachineConfigFilePath;
+        }
+
+        public ConfigurationFileMap(string machineConfigFilename) {
+            if (string.IsNullOrEmpty(machineConfigFilename))
+                throw new ArgumentNullException("machineConfigFilename");
+            if (!File.Exists(machineConfigFilename))
+                throw new ArgumentException(SR.GetString(SR.Machine_config_file_not_found, machineConfigFilename), "machineConfigFilename");
+
+            MachineConfigFilename = machineConfigFilename;
+        }
+
+        // copy ctor used only for cloning
+        private ConfigurationFileMap(ConfigurationFileMap other) {
+            _getFilenameThunk = other._getFilenameThunk;
+        }
+
+        public virtual object Clone() {
+            return new ConfigurationFileMap(this);
+        }
+
+        private static string GetFilenameFromMachineConfigFilePath() {
+            string filename = ClientConfigurationHost.MachineConfigFilePath;
+            new FileIOPermission(FileIOPermissionAccess.PathDiscovery, filename).Demand();
+            return filename;
+        }
+
+        //
+        // The name of machine.config.
+        //
+        public string MachineConfigFilename {
+            get {
+                return _getFilenameThunk();
+            }
+            set {
+                _getFilenameThunk = () => value;
+            }
+        }
+    }
+}