Explicit Serialization API and Security

Peter Firmstone peter.firmstone at zeus.net.au
Wed Jan 14 12:58:54 UTC 2015

Hi Chris,

Sorry, no.

Currently when an ObjectStreamClass is read in from the stream, the framework searches for the first zero arg constructor of a non serializable class and creates and instance of the class read and resolved from the stream, however it does so using a super class constructor.

Then from the super class down, fields are read in and set in order for each class in the object's inheritance hierarchy.

The alternative I propose, doesn't create the instance, instead it reads the fields from the stream, one by one and without instantiating them, if they are newly read objects, stores them temporarily into byte [] arrays in a Map with reference handle keys, otherwise it just holds the reference handle.

What it does next is wrap this information into a caller sensitive api, GetFields or ReadSerial instance, that is passed as a constructor parameter to the child class serial constructor.

The child class checks invariants and reads each field it needs using a static method prior to calling a superclass constructor, each class in the inheritance hierarchy for the object then checks its invariants until it gets to the first non serializable superclass.

The benefit of this order is that each class is present in the thread security context, so protection domain security and invariants are enforced before instantiating an object.  

Hope this helps illuminate it a little better, regards,


----- Original message -----
> Peter F,
> I am still struggling with the basic concept of you proposal. Let me see 
> if I understand it correctly. Does the following describe a similar 
> scenario as you envisage:
>     1) For each Serializable type, T, in the deserialized types
>           hierarchy, starting with the top most ( closest to j.l.Object ),
>           1a) Read T's fields from the stream, fields
>           1b) validate(t, fields)   // t will be null first time
>           1c) allocate a new instance of T, and assign to t
>           1d) set fields in t
>     2) Return t;
> So for each level in the hierarchy, an instance of a type is created 
> only after its invariants have been checked. This instance is then 
> passed to the next level so it can participate in that levels invariants 
> validation.
> If this scenario is along the same lines as yours, then I just don't see 
> how 1c above will always be possible.
> If we could somehow make the object caller sensitive until after 
> deserialization completes, then could avoid having to try to allocate 
> multiple instance down the hierarchy.
> -Chris.
> On 13/01/15 10:24, Peter Firmstone wrote:
> > Could we use a static validator method and generate bytecode for
> > constructors dynamically?
> > 
> > The developer can optionally implement the constructors.
> > 
> > static GetField invariantCheck(GetField f);
> > 
> > Create a caller sensitive GetField implementation and add a two new
> > methods to GetField:
> > 
> > abstract Object createSuper(); // to access superclass object methods
> > for inavariant checking.
> > 
> > abstract Class getType(String name);
> > 
> > Set fields from within constructors.
> > 
> > The generated constructors are straight forward:
> > 
> > 1. Call static method.
> > 2. Call super class constructor with result from static method.
> > 3. Set final fields
> > 4. How to set transient fields, implement a private method called from
> > within the constructor?
> > 
> > Require a permission to extend GetField?
> > 

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