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

Wed Dec 23 10:47:00 GMT 2009

On 12/23/2009 10:38 AM, Erik Groeneveld wrote:
> 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 Â´hasNextÂ´ 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.

How can there be 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年04月16日 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?

Yes, but can you send a test case before we go any further? Then at least
we'll all know what you're talking about.
Andrew.