On 09/03/2013 07:26 PM, Nick Williams wrote:
On Sep 3, 2013, at 12:16 PM, Peter Levart wrote:
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.@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.
That's exactly what I said, just worded differently.
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.
Now that's a change that makes sense and would certainly be more user-friendly.
Keep @CallerSensitive private, but don't require it for
StackTraceFrame#getCallerClass()/getCallerFrame(). Document that
StackTraceFrame should not be used to make security decisions. Still require
@CallerSensitive for Reflection#getCallerClass(). I like this idea.
***
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).
Absolutely not. This would be orders of magnitude slower than what I've
implemented,
Not necessarily. If using internal Class/ClassLoader API (accessible
only to java.lang classes, but StackTraceFrame is java.lang class), this
might be implemented without security manager checks.
not to mention that it wouldn't even stop any security problem, if one exists.
On can simply use reflection to get the declaringClass field value regardless
of what getDeclaringClass returns.
One can simply use reflection to do practically anything if no security
manager is installed. If it is, and security policy does not allow it,
then you can not access private fields with reflection.
Regards, Peter
N
Regards, Peter
