RFR 8212937: Parent class loader may not have a referred ClassLoaderData instance when obtained in Klass::class_in_module_of_loader

[Severin Gehwolf]

On Thu, 2018-10-25 at 12:15 -0300, Martin Balao wrote:
> Hi Lois,
> 
> Thanks for having a look at this.
> 
> Yes, I have a test that triggers this execution path. Unfortunately, this
> is a security test that I cannot publicly share. What I can tell you,
> though, is that the parent class loader is a "delegating class loader"
> which never defined a class and that's the reason why it doesn't have a
> ClassLoaderData instance created.
> 
> I'm not sure if this would be needed in other places where the idiom is not
> used. The reason is that there might be any other implicit assumptions that
> makes it impossible. That's why I limited the scope of this changeset to
> the only case that I'm sure it's possible to trigger.

FWIW, I can confirm that the proposed patch fixes the issue we were
seeing.

Thanks,
Severin


On Wed, Oct 24, 2018 at 5:52 PM, Lois Foltan <lois.foltan at oracle.com>
wrote:
> 
> > On 10/24/2018 3:58 PM, Martin Balao wrote:
> > 
> > Hi,
> > > 
> > > Can I have a review for JDK-8212937 [1]?
> > > 
> > > Webrev.00:
> > > 
> > >   * http://cr.openjdk.java.net/~mbalao/webrevs/8212937/8212937.webrev.00/
> > >   * http://cr.openjdk.java.net/~mbalao/webrevs/8212937/8212937.
> > > webrev.00.zip
> > > 
> > > By obtaining the ClassLoaderData instance through a call to
> > > SystemDictionary::register_loader, we make sure that either an existing
> > > instance is obtained or a new one created. This same idiom has already
> > > been
> > > used in other places where there are no guarantees that a previous
> > > ClassLoaderData instance exists for a given class loader. See futher
> > > information in JDK-8212937 ticket [1].
> > > 
> > > Thanks,
> > > Martin.-
> > > 
> > > --
> > > [1] - https://bugs.openjdk.java.net/browse/JDK-8212937
> > > 
> > 
> > Hi Martin,
> > 
> > I agree that the same idiom is used in other places, but there are also a
> > couple of occurrences of java_lang_ClassLoader::parent in
> > classfile/classLoaderStats.cpp and classfile/classLoaderHierarchyDCmd.cpp
> > that do not.  In order to better understand, do you have a test case that
> > demonstrates this issue?
> > 
> > Thanks,
> > Lois
> >