RFR(S) 8160987: JDWP ClassType.InvokeMethod doesn't validate class

David Holmes david.holmes at oracle.com
Fri Sep 16 02:13:15 UTC 2016

On 16/09/2016 8:52 AM, serguei.spitsyn at oracle.com wrote:
> Hi Harold,
> I did not got deep into the fix yet but wonder why the JVMTI function is
> not used.

I was wondering a similar thing. It seems very heavyweight to use Java 
level reflection from inside native code to validate the native 
"handles" passed to that native code. I would have expected a way to go 
from a MethodId to the declaring class of the method, and a simple way 
to test if there is an ancestor relation between the two classes.

> On 9/15/16 13:05, harold seigel wrote:
>> One could argue that a spec compliant JNI implementation wouldn't need
>> this change in the first place...
>> Regardless, I'm withdrawing this change because I found that it fails
>> a com/sun/jdi JTreg test involving static methods in interfaces.

I find it both intriguing and worrying that ClassType.InvokeMethod 
refers to superinterfaces when prior to 8 (and this spec was not updated 
in this area) static interface methods did not exist! The main changes 
were in the definition of InterfaceType.InvokeMethod. I wonder whether 
invocation of static interface methods via ClassType.InvokeMethod is 
actually tested directly?

I realize the specs are a bit of a minefield when it comes to what is 
required by the different specs and what is implemented in hotspot. 
Unfortunately it is a minefield I also have to wade through for private 
interface methods. In many cases it is not clear what should happen and 
all we have to guide us is what hotspot does (eg "virtual" invocations 
on non-virtual methods).


>> Thanks, Harold
>> On 9/15/2016 3:37 PM, Daniel D. Daugherty wrote:
>>> On 9/15/16 12:10 PM, harold seigel wrote:
>>>> (Adding hotspot-runtime)
>>>> Hi Dan,
>>>> Thanks for looking at this.
>>>> I could pass NULL instead of clazz to ToReflectMethod() to ensure
>>>> that the method object isn't being obtained from clazz.
>>> I don't think that would be a JNI spec compliant use of the
>>> JNI ToReflectedMethod() function. That would be relying on
>>> the fact that HotSpot doesn't use the clazz parameter to
>>> convert {clazz,jmethodID} => method_object.
>>> Sorry... again...
>>> Dan
>>>> Harold
>>>> On 9/15/2016 1:09 PM, Daniel D. Daugherty wrote:
>>>>> On 9/15/16 9:31 AM, harold seigel wrote:
>>>>>> Hi,
>>>>>> Please review this small fix for JDK-8160987.  The JDWP
>>>>>> InvokeStatic() method was depending on the JNI function that it
>>>>>> called to enforce the requirement that the specified method must
>>>>>> be a member of the specified class or one of its super classes.
>>>>>> But, JNI does not enforce this requirement. This fix adds code to
>>>>>> JDWP to do its own check that the specified method is a member of
>>>>>> the specified class or one of its super classes.
>>>>>> JBS Bug: https://bugs.openjdk.java.net/browse/JDK-8160987
>>>>>> Open webrev: http://cr.openjdk.java.net/~hseigel/bug_8160987/
>>>>> src/jdk.jdwp.agent/share/native/libjdwp/invoker.c
>>>>>     Sorry I didn't think of this comment during the pre-review...
>>>>>     The only "strange" part of this fix is:
>>>>>     L374:     /* Get the method object from the method's jmethodID. */
>>>>>     L375:     method_object = JNI_FUNC_PTR(env,ToReflectedMethod)(env,
>>>>>     L376: clazz,
>>>>>     L377: method,
>>>>>     L378: JNI_TRUE /* isStatic */);
>>>>>     L379:     if (method_object == NULL) {
>>>>>     L380:         return JVMTI_ERROR_NONE; /* Bad jmethodID ? This
>>>>> will be handled elsewhere */
>>>>>     L381:     }
>>>>>     Here we are using parameter 'clazz' to find the method_object for
>>>>>     parameter 'method' so that we can validate that 'clazz' refers to
>>>>>     method's class or superclass.
>>>>>     When a bogus 'clazz' value is passed in by a JCK test, the only
>>>>>     reason that JNI ToReflectedMethod() can still find the right
>>>>>     method_object is that our (HotSpot) implementation of JNI
>>>>>     ToReflectedMethod() doesn't really require the 'clazz' parameter
>>>>>     to find the right method_object. So the 'method_object' that we
>>>>>     return is the real one which has a 'clazz' field that doesn't
>>>>>     match the 'clazz' parameter.
>>>>>     Wow does that twist your head around or what?
>>>>>     So we're trusting JNI ToReflectedMethod() to return the right
>>>>>     method_object when we give it a potentially bad 'clazz' value.
>>>>>     So should we use JNI FromReflectedMethod() to convert the
>>>>>     method_object back into a jmethodID and verify that jmethodID
>>>>>     matches the one that we passed to check_methodClass()?
>>>>> I might be too paranoid here so feel free to say that enough is
>>>>> enough with this fix.
>>>>> Thumbs up!
>>>>> Dan
>>>>>> The fix was tested with the two failing JCK vm/jdwp tests listed
>>>>>> in the bug, the JCK Lang, VM, and API tests, the hotspot JTReg
>>>>>> tests, the java/lang, java/util and other JTReg tests, the
>>>>>> co-located and non-colocated NSK tests, and with the RBT Tier2 tests.
>>>>>> Thanks, Harold

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