problem with class accessiblity check in invoke (natMethod.cc)

[Erik Groeneveld]

L.S.

We recently upgraded from libgcj7 to libgcj9. This broke our code. We
found out that in natMethod.cc in invoke() there is an additional
check for class accessibility. It starts out with:

  // Check accessibility, if required.
  if (! this->isAccessible())
    {
      if (! (Modifier::isPublic (meth->accflags)))
	{
	  Class *caller = _Jv_StackTrace::GetCallingClass (&Method::class$);
	  if (! _Jv_CheckAccess(caller, declaringClass, meth->accflags))
	    throw new IllegalAccessException;
	}

and then continues here (this part is new):

      else
	// Method is public, check to see if class is accessible.
	{
	  jint flags = (declaringClass->accflags
			& (Modifier::PUBLIC
			   | Modifier::PROTECTED
			   | Modifier::PRIVATE));
	  if (flags == 0) // i.e. class is package private
	    {
	      Class *caller = _Jv_StackTrace::GetCallingClass (&Method::class$);
	      if (! _Jv_ClassNameSamePackage (caller->name,
					      declaringClass->name))
		throw new IllegalAccessException;
	    }
	}
    }

The added code prevents legal calls to fail. For example, it is no
longer possible to call invoke on the ´hasNext´ method on the iterator
from AbstractList.  The method AbstractList.iterator() returns an
anonymous innerclass object which according to the C code above is not
accessible since it is package private.  There are two problems here:

1. The systems segfaults on the caller->name because there is no calling class.
2. We believe class accessibility is not relevant here: there is no
reason why a Method object with public access should not be invokable,
or is there?

We found the following modification log, which is why we address
Andrew Haley directly as well as the list:

2007-04-16  Andrew Haley  <aph@redhat.com>

        * java/lang/reflect/natMethod.cc (Method::invoke): In invoke also
        check that the method's declaring class is accessible.

Can you or anybody else explain why this was considered to be necessary?

Yours,
Erik J. Groeneveld and Jurjan-Paul Medema