Explicit Serialization API and Security

[Chris Hegarty]

On 14/01/15 12:58, Peter Firmstone wrote:
> 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.

This is my understanding also.

> 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.

GetField.get(...), or ReadSerial, will create an object before returning 
it. So the invariant checker methods will turn the stream field values 
into objects at some point.

Also, from your previous examples, I though I seen the invariant checker 
method explicitly create superclass instance, so that it could be used 
in the validation, right?

What I was trying to do was to reduce your examples, and description, 
into a sequence of steps, to try to better understand how this would work.

What I came up with, I believe, is equivalent to what was done in this 
example [1]. If you intend to chain the "serial constructors" up with 
static check methods that create superclass instances, then I think is 
equates to top-down checking as I have described it.


> 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,


-Chris.

[1] 
http://mail.openjdk.java.net/pipermail/core-libs-dev/2015-January/030550.html

>
> Peter.
>
> ----- 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?
>  > >
>