--- /dev/null
+// 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.
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Diagnostics.Contracts;
+using System.Reflection;
+using System.Security;
+
+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
+ // m_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 m_safeSerializationManager;
+ //
+ // 2. Add a protected SerializeObjectState event, which passes through to the SafeSerializationManager:
+ //
+ // protected event EventHandler<SafeSerializationEventArgs> SerializeObjectState
+ // {
+ // add { m_safeSerializationManager.SerializeObjectState += value; }
+ // remove { m_safeSerializationManager.SerializeObjectState -= value; }
+ // }
+ //
+ // 3. Serialize the safe serialization object in GetObjectData, and call its CompleteSerialization method:
+ //
+ // [SecurityCritical]
+ // void ISerializable.GetObjectData(SerializationInfo info, StreamingContext context)
+ // {
+ // info.AddValue("m_safeSerializationManager", m_safeSerializationManager, typeof(SafeSerializationManager));
+ // m_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)
+ // {
+ // m_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 m_extraData;
+ //
+ // void ISafeSerializationData.CompleteDeserialization(object obj)
+ // {
+ // TransparentException exception = obj as TransparentException;
+ // exception.m_state = this;
+ // }
+ // }
+ //
+ // [NonSerialized]
+ // private TransparentExceptionState m_state = new TransparentExceptionState();
+ //
+ // public TransparentException()
+ // {
+ // SerializeObjectState += delegate(object exception, SafeSerializationEventArgs eventArgs)
+ // {
+ // eventArgs.AddSerializedState(m_state);
+ // };
+ // }
+ //
+ // public string ExtraData
+ // {
+ // get { return m_state.m_extraData; }
+ // set { m_state.m_extraData = value; }
+ // }
+ // }
+ //
+
+ // SafeSerializationEventArgs are provided to the delegates which do safe serialization. Each delegate
+ // serializes its own state into an IDeserializationCallback instance which must, itself, be serializable.
+ // These indivdiual states are then added to the SafeSerializationEventArgs in order to be saved away when
+ // the original ISerializable type is serialized.
+ public sealed class SafeSerializationEventArgs : EventArgs
+ {
+ private StreamingContext m_streamingContext;
+ private List<object> m_serializedStates = new List<object>();
+
+ internal SafeSerializationEventArgs(StreamingContext streamingContext)
+ {
+ m_streamingContext = streamingContext;
+ }
+
+ public void AddSerializedState(ISafeSerializationData serializedState)
+ {
+ if (serializedState == null)
+ throw new ArgumentNullException("serializedState");
+ if (!serializedState.GetType().IsSerializable)
+ throw new ArgumentException(Environment.GetResourceString("Serialization_NonSerType", serializedState.GetType(), serializedState.GetType().Assembly.FullName));
+
+ m_serializedStates.Add(serializedState);
+ }
+
+ internal IList<object> SerializedStates
+ {
+ get { return m_serializedStates; }
+ }
+
+ public StreamingContext StreamingContext
+ {
+ get { return m_streamingContext; }
+ }
+ }
+
+ // 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);
+ }
+#if FEATURE_SERIALIZATION
+ // Helper class to implement safe serialization. Concrete ISerializable types which want to allow
+ // transparent subclasses code to participate in serialization should contain an instance of
+ // SafeSerializationManager and wire up to it as described in code:#SafeSerialization.
+ [Serializable]
+ internal sealed class SafeSerializationManager : IObjectReference, ISerializable
+ {
+ // Saved states to store in the serialization stream. This is typed as object rather than
+ // ISafeSerializationData because ISafeSerializationData can't be marked serializable.
+ private IList<object> m_serializedStates;
+
+ // This is the SerializationInfo that is used when the SafeSerializationManager type has replaced
+ // itself as the target of serialziation. It is not used directly by the safe serialization code,
+ // but just held onto so that the real object being deserialzed can use it later.
+ private SerializationInfo m_savedSerializationInfo;
+
+ // Real object that we've deserialized - this is stored when we complete construction and calling
+ // the deserialization .ctors on it and is used when we need to notify the stored safe
+ // deserialization data that they should populate the object with their fields.
+ private object m_realObject;
+
+ // Real type that should be deserialized
+ private RuntimeType m_realType;
+
+ // Event fired when we need to collect state to serialize into the parent object
+ internal event EventHandler<SafeSerializationEventArgs> SerializeObjectState;
+
+ // Name that is used to store the real type being deserialized in the main SerializationInfo
+ private const string RealTypeSerializationName = "CLR_SafeSerializationManager_RealType";
+
+ internal SafeSerializationManager()
+ {
+ }
+
+ [SecurityCritical]
+ private SafeSerializationManager(SerializationInfo info, StreamingContext context)
+ {
+ // We need to determine if we're being called to really deserialize a SafeSerializationManager,
+ // or if we're being called because we've intercepted the deserialization callback for the real
+ // object being deserialized. We use the presence of the RealTypeSerializationName field in the
+ // serialization info to indicate that this is the interception callback and we just need to
+ // safe the info. If that field is not present, then we should be in a real deserialization
+ // construction.
+ RuntimeType realType = info.GetValueNoThrow(RealTypeSerializationName, typeof(RuntimeType)) as RuntimeType;
+
+ if (realType == null)
+ {
+ m_serializedStates = info.GetValue("m_serializedStates", typeof(List<object>)) as List<object>;
+ }
+ else
+ {
+ m_realType = realType;
+ m_savedSerializationInfo = info;
+ }
+ }
+
+ // Determine if the serialization manager is in an active state - that is if any code is hooked up
+ // to use it for serialization
+ internal bool IsActive
+ {
+ get { return SerializeObjectState != null; }
+ }
+
+ // CompleteSerialization is called by the base ISerializable in its GetObjectData method. It is
+ // responsible for gathering up the serialized object state of any delegates that wish to add their
+ // own state to the serialized object.
+ [SecurityCritical]
+ internal void CompleteSerialization(object serializedObject,
+ SerializationInfo info,
+ StreamingContext context)
+ {
+ Contract.Requires(serializedObject != null);
+ Contract.Requires(info != null);
+ Contract.Requires(typeof(ISerializable).IsAssignableFrom(serializedObject.GetType()));
+ Contract.Requires(serializedObject.GetType().IsAssignableFrom(info.ObjectType));
+
+ // Clear out any stale state
+ m_serializedStates = null;
+
+ // We only want to kick in our special serialization sauce if someone wants to participate in
+ // it, otherwise if we have no delegates registered there's no reason for us to get in the way
+ // of the regular serialization machinery.
+ EventHandler<SafeSerializationEventArgs> serializeObjectStateEvent = SerializeObjectState;
+ if (serializeObjectStateEvent != null)
+ {
+ // Get any extra data to add to our serialization state now
+ SafeSerializationEventArgs eventArgs = new SafeSerializationEventArgs(context);
+ serializeObjectStateEvent(serializedObject, eventArgs);
+ m_serializedStates = eventArgs.SerializedStates;
+
+ // Replace the type to be deserialized by the standard serialization code paths with
+ // ourselves, which allows us to control the deserialization process.
+ info.AddValue(RealTypeSerializationName, serializedObject.GetType(), typeof(RuntimeType));
+ info.SetType(typeof(SafeSerializationManager));
+ }
+ }
+
+ // CompleteDeserialization is called by the base ISerializable object's OnDeserialized handler to
+ // finish the deserialization of the object by notifying the saved states that they should
+ // re-populate their portions of the deserialized object.
+ internal void CompleteDeserialization(object deserializedObject)
+ {
+ Contract.Requires(deserializedObject != null);
+
+ if (m_serializedStates != null)
+ {
+ foreach (ISafeSerializationData serializedState in m_serializedStates)
+ {
+ serializedState.CompleteDeserialization(deserializedObject);
+ }
+ }
+ }
+
+ [SecurityCritical]
+ void ISerializable.GetObjectData(SerializationInfo info, StreamingContext context)
+ {
+ info.AddValue("m_serializedStates", m_serializedStates, typeof(List<IDeserializationCallback>));
+ }
+
+ // GetRealObject intercepts the deserialization process in order to allow deserializing part of the
+ // object's inheritance heirarchy using standard ISerializable constructors, and the remaining
+ // portion using the saved serialization states.
+ [SecurityCritical]
+ object IObjectReference.GetRealObject(StreamingContext context)
+ {
+ // If we've already deserialized the real object, use that rather than deserializing it again
+ if (m_realObject != null)
+ {
+ return m_realObject;
+ }
+
+ // If we don't have a real type to deserialize, then this is really a SafeSerializationManager
+ // and we don't need to rebuild the object that we're standing in for.
+ if (m_realType == null)
+ {
+ return this;
+ }
+
+ // Look for the last type in GetRealType's inheritance hierarchy which implements a critical
+ // deserialization constructor. This will be the object that we use as the deserialization
+ // construction type to initialize via standard ISerializable semantics
+
+ // First build up the chain starting at the type below Object and working to the real type we
+ // serialized.
+ Stack inheritanceChain = new Stack();
+ RuntimeType currentType = m_realType;
+ do
+ {
+ inheritanceChain.Push(currentType);
+ currentType = currentType.BaseType as RuntimeType;
+ }
+ while (currentType != typeof(object));
+
+ // Now look for the first type that does not implement the ISerializable .ctor. When we find
+ // that, previousType will point at the last type that did implement the .ctor. We require that
+ // the .ctor we invoke also be non-transparent
+ RuntimeConstructorInfo serializationCtor = null;
+ RuntimeType previousType = null;
+ do
+ {
+ previousType = currentType;
+ currentType = inheritanceChain.Pop() as RuntimeType;
+ serializationCtor = currentType.GetSerializationCtor();
+ }
+ while (serializationCtor != null && serializationCtor.IsSecurityCritical);
+
+ // previousType is the last type that did implement the deserialization .ctor before the first
+ // type that did not, so we'll grab it's .ctor to use for deserialization.
+ BCLDebug.Assert(previousType != null, "We should have at least one inheritance from the base type");
+ serializationCtor = ObjectManager.GetConstructor(previousType);
+
+ // Allocate an instance of the final type and run the selected .ctor on that instance to get the
+ // standard ISerializable initialization done.
+ object deserialized = FormatterServices.GetUninitializedObject(m_realType);
+ serializationCtor.SerializationInvoke(deserialized, m_savedSerializationInfo, context);
+ m_savedSerializationInfo = null;
+ m_realType = null;
+
+ // Save away the real object that was deserialized so that we can fill it in later, and return
+ // it back as the object that should result from the final deserialization.
+ m_realObject = deserialized;
+ return deserialized;
+ }
+
+ [OnDeserialized]
+ private void OnDeserialized(StreamingContext context)
+ {
+ // We only need to complete deserialization if we were hooking the deserialization process. If
+ // we have not deserialized an object in the GetRealObject call, then there's nothing more for
+ // us to do here.
+ if (m_realObject != null)
+ {
+ // Fire the real object's OnDeserialized method if they registered one. Since we replaced
+ // ourselves as the target of the deserialization, OnDeserialized on the target won't
+ // automatically get triggered unless we do it manually.
+ SerializationEvents cache = SerializationEventsCache.GetSerializationEventsForType(m_realObject.GetType());
+ cache.InvokeOnDeserialized(m_realObject, context);
+ m_realObject = null;
+ }
+ }
+ }
+#endif
+}
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