Replacement of sun.reflect.Reflection#getCallerClass

[Peter Levart]

On 09/03/2013 04:39 PM, Nick Williams wrote:
>> >Do you mean sun.reflect.CallerSensitive can go away?  This is very important part of the design that we need to detect which methods are caller-sensitive.   I keep seeing you suggest this and it is unclear to me if you only mean to remove java.lang. at CallerSensitive in your proposal.
> Yes, that's what I mean. If you carefully examine the (existing) native code that backs getCallerClass, you see that @CallerSensitive is/only/  used as an enforcement mechanism. When I first read about @CallerSensitive, I/thought/  you could take a call stack like this one:
>
> @CallerSensitive getCallerClass()
> @CallerSensitive someMethod1()
> @CallerSensitive someMethod2()
> @CallerSensitive someMethod3()
> @CallerSensitive someMethod4()
> actualCallerMethod()
>
> And calling getCallerClass would return the class for actualCallerMethod(). However, I was wrong. getCallerClass/always/  returns someMethod1(). @CallerSensitive is/not/  used to determine when to stop looking for the caller. It's just an enforcement mechanism to ensure that only built-in JVM classes can call getCallerClass.

*AND* that Reflection.getCallerClass() can only be called from within 
methods annotated with @CallerSensitive.

Now for that part, the public API equivalent 
(StackTraceFrame.getCallerClass() or whatever it is called) need not be 
restricted to methods annotated with any annotation, but that means that 
this public API should not be used to implement security decisions since 
MethodHandles API allows caller to be spoofed unless looking-up a method 
annotated with @CallerSensitive...

>   This is/not/  how I did it, this is how it already was. Because of this, you could delete the @CallerSensitive annotation completely and getCallerClass still be fully functional the way it is. It just wouldn't be restricted to annotated methods anymore.

For security unrelated things (like logging and similar) public API need 
not include any enabling annotation, but it needs to be documented that 
it should not be used for security decisions.

***

Regarding ability to obtain j.l.Class instances for classes that client 
code would otherwise have no access to:

What about a simple restriction on methods returning such instances that 
Class objects are only returned when they are resolvable from the 
ClassLoader of client code. If they are not resolvable, null is 
returned. For example, the equivalent of:

public class StackTraceFrame {

     private final Class<?> declaringClass;

     @CallerSensitive
     public Class<?> getDeclaringClass() {
         try {
             return Class.forName(declaringClass.getName(),
                                  false,
Reflection.getCallerClass().getClassLoader())
                    == declaringClass ? declaringClass : null;
             }
         } catch (ClassNotFoundException ignore) {}
         return null;
     }

     // the name can be exposed without fear...
     public String getDeclaringClassName() {
         return declaringClass.getName();
     }


This example could be implemented more efficiently then above code 
(using private Class/ClassLoader API).

Regards, Peter