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Diffstat (limited to 'src/mscorlib/shared/System/Runtime/Serialization/ISafeSerializationData.cs')
| -rw-r--r-- | src/mscorlib/shared/System/Runtime/Serialization/ISafeSerializationData.cs | 207 |
1 files changed, 207 insertions, 0 deletions
diff --git a/src/mscorlib/shared/System/Runtime/Serialization/ISafeSerializationData.cs b/src/mscorlib/shared/System/Runtime/Serialization/ISafeSerializationData.cs new file mode 100644 index 0000000000..5089d134c3 --- /dev/null +++ b/src/mscorlib/shared/System/Runtime/Serialization/ISafeSerializationData.cs @@ -0,0 +1,207 @@ +// Licensed to the .NET Foundation under one or more agreements. +// The .NET Foundation licenses this file to you under the MIT license. +// See the LICENSE file in the project root for more information. + +namespace System.Runtime.Serialization +{ + // + // #SafeSerialization + // + // Types which are serializable via the ISerializable interface have a problem when it comes to allowing + // transparent subtypes which can allow themselves to serialize since the GetObjectData method is + // SecurityCritical. + // + // For instance, System.Exception implements ISerializable, however it is also desirable to have + // transparent exceptions with their own fields that need to be serialized. (For instance, in transparent + // assemblies such as the DLR and F#, or even in partial trust application code). Since overriding + // GetObjectData requires that the overriding method be security critical, this won't work directly. + // + // SafeSerializationManager solves this problem by allowing any partial trust code to contribute + // individual chunks of serializable data to be included in the serialized version of the derived class. + // These chunks are then deserialized back out of the serialized type and notified that they should + // populate the fields of the deserialized object when serialization is complete. This allows partial + // trust or transparent code to participate in serialization of an ISerializable type without having to + // override GetObjectData or implement the ISerializable constructor. + // + // On the serialization side, SafeSerializationManager has an event SerializeObjectState which it will + // fire in response to serialization in order to gather the units of serializable data that should be + // stored with the rest of the object during serialization. Methods which respond to these events + // create serializable objects which implement the ISafeSerializationData interface and add them to the + // collection of other serialized data by calling AddSerializedState on the SafeSerializationEventArgs + // passed into the event. + // + // By using an event rather than a virtual method on the base ISerializable object, we allow multiple + // potentially untrusted subclasses to participate in serialization, without each one having to ensure + // that it calls up to the base type in order for the whole system to work. (For instance Exception : + // TrustedException : UntrustedException, in this scenario UntrustedException would be able to override + // the virtual method an prevent TrustedException from ever seeing the method call, either accidentally + // or maliciously). + // + // Further, by only allowing additions of new chunks of serialization state rather than exposing the + // whole underlying list, we avoid exposing potentially sensitive serialized state to any of the + // potentially untrusted subclasses. + // + // At deserialization time, SafeSerializationManager performs the reverse operation. It deserializes the + // chunks of serialized state, and then notifies them that the object they belong to is deserialized by + // calling their CompleteSerialization method. In repsonse to this call, the state objects populate the + // fields of the object being deserialized with the state that they held. + // + // From a security perspective, the chunks of serialized state can only contain data that the specific + // subclass itself had access to read (otherwise it wouldn't be able to populate the type with that + // data), as opposed to having access to far more data in the SerializationInfo that GetObjectData uses. + // Similarly, at deserialization time, the serialized state can only modify fields that the type itself + // has access to (again, as opposed to the full SerializationInfo which could be modified). + // + // Individual types which wish to participate in safe serialization do so by containing an instance of a + // SafeSerializationManager and exposing its serialization event. During GetObjectData, the + // SafeSerializationManager is serialized just like any other field of the containing type. However, at + // the end of serialization it is called back one last time to CompleteSerialization. + // + // In CompleteSerialization, if the SafeSerializationManager detects that it has extra chunks of + // data to handle, it substitutes the root type being serialized (formerly the real type hosting the + // SafeSerializationManager) with itself. This allows it to gain more control over the deserialization + // process. It also saves away an extra bit of state in the serialization info indicating the real type + // of object that should be recreated during deserialization. + // + // At this point the serialized state looks like this: + // Data: + // realSerializedData1 + // ... + // realSerializedDataN + // safeSerializationData -> this is the serialization data member of the parent type + // _serializedState -> list of saved serialized states from subclasses responding to the safe + // serialization event + // RealTypeSerializationName -> type which is using safe serialization + // Type: + // SafeSerializationManager + // + // That is, the serialized data claims to be of type SafeSerializationManager, however contains only the + // data from the real object being serialized along with one bit of safe serialization metadata. + // + // At deserialization time, since the serialized data claims to be of type SafeSerializationManager, the + // root object being created is an instance of the SafeSerializationManager class. However, it detects + // that this isn't a real SafeSerializationManager (by looking for the real type field in the metadata), + // and simply saves away the SerializationInfo and the real type being deserialized. + // + // Since SafeSerializationManager implements IObjectReference, the next step of deserialization is the + // GetRealObject callback. This callback is the one responsible for getting the + // SafeSerializationManager out of the way and instead creating an instance of the actual type which was + // serialized. + // + // It does this by first creating an instance of the real type being deserialzed (saved away in the + // deserialzation constructor), but not running any of its constructors. Instead, it walks the + // inheritance hierarchy (moving toward the most derived type) looking for the last full trust type to + // implement the standard ISerializable constructor before any type does not implement the constructor. + // It is this last type's deserialization constructor which is then invoked, passing in the saved + // SerializationInfo. Once the constructors are run, we return this object as the real deserialized + // object. + // + // The reason that we do this walk is so that ISerializable types can protect themselves from malicious + // input during deserialization by making their deserialization constructors unavailable to partial + // trust code. By not requiring every type have a copy of this constructor, partial trust code can + // participate in safe serialization and not be required to have access to the parent's constructor. + // + // It should be noted however, that this heuristic means that if a full trust type does derive from + // a transparent or partial trust type using this safe serialization mechanism, that full trust type + // will not have its constructor called. Further, the protection of not invoking partial trust + // deserialization constructors only comes into play if SafeSerializationManager is in control of + // deserialization, which means there must be at least one (even empty) safe serialization event + // handler registered. + // + // Another interesting note is that at this point there are now two SafeSerializationManagers alive for + // this deserialization. The first object is the one which is controlling the deserialization and was + // created as the root object of the deserialization. The second one is the object which contains the + // serialized data chunks and is a data member of the real object being deserialized. For this reason, + // the data objects cannot be notified that the deserialization is complete during GetRealObject since + // the ISafeSerializationData objects are not members of the active SafeSerializationManager instance. + // + // The next step is the OnDeserialized callback, which comes to SafeSerializableObject since it was + // pretending to be the root object of the deserialization. It responds to this callback by calling + // any existing OnDeserialized callback on the real type that was deserialized. + // + // The real type needs to call its data member SafeSerializationData object's CompleteDeserialization + // method in response to the OnDeserialized call. This CompleteDeserialization call will then iterate + // through the ISafeSerializationData objects calling each of their CompleteDeserialization methods so + // that they can plug the nearly-complete object with their saved data. + // + // The reason for having a new ISafeSerializationData interface which is basically identical to + // IDeserializationCallback is that IDeserializationCallback will be called on the stored data chunks + // by the serialization code when they are deserialized, and that's not a desirable behavior. + // Essentially, we need to change the meaning of the object parameter to mean "parent object which + // participated in safe serialization", rather than "this object". + // + // Implementing safe serialization on an ISerialiable type is relatively straight forward. (For an + // example, see System.Exception): + // + // 1. Include a data member of type SafeSerializationManager: + // + // private SafeSerializationManager _safeSerializationManager; + // + // 2. Add a protected SerializeObjectState event, which passes through to the SafeSerializationManager: + // + // protected event EventHandler<SafeSerializationEventArgs> SerializeObjectState + // { + // add { _safeSerializationManager.SerializeObjectState += value; } + // remove { _safeSerializationManager.SerializeObjectState -= value; } + // } + // + // 3. Serialize the safe serialization object in GetObjectData, and call its CompleteSerialization method: + // + // { + // info.AddValue("_safeSerializationManager", _safeSerializationManager, typeof(SafeSerializationManager)); + // _safeSerializationManager.CompleteSerialization(this, info, context); + // } + // + // 4. Add an OnDeserialized handler if one doesn't already exist, and call CompleteDeserialization in it: + // + // [OnDeserialized] + // private void OnDeserialized(StreamingContext context) + // { + // _safeSerializationManager.CompleteDeserialization(this); + // } + // + // On the client side, using safe serialization is also pretty easy. For example: + // + // [Serializable] + // public class TransparentException : Exception + // { + // [Serializable] + // private struct TransparentExceptionState : ISafeSerializationData + // { + // public string _extraData; + // + // void ISafeSerializationData.CompleteDeserialization(object obj) + // { + // TransparentException exception = obj as TransparentException; + // exception._state = this; + // } + // } + // + // [NonSerialized] + // private TransparentExceptionState _state = new TransparentExceptionState(); + // + // public TransparentException() + // { + // SerializeObjectState += delegate(object exception, SafeSerializationEventArgs eventArgs) + // { + // eventArgs.AddSerializedState(_state); + // }; + // } + // + // public string ExtraData + // { + // get { return _state._extraData; } + // set { _state._extraData = value; } + // } + // } + // + + // Interface to be supported by objects which are stored in safe serialization stores + public interface ISafeSerializationData + { + // CompleteDeserialization is called when the object to which the extra serialized data was attached + // has completed its deserialization, and now needs to be populated with the extra data stored in + // this object. + void CompleteDeserialization(object deserialized); + } +} |