[9] RFR(S): 8139150: ClassVerifier frees exception message while it's still in use

[Tobias Hartmann]

Hi Daniel,

On 08.10.2015 18:08, Daniel D. Daugherty wrote:
> On 10/8/15 9:38 AM, Tobias Hartmann wrote:
>> Hi,
>>
>> please review the following patch.
>>
>> https://bugs.openjdk.java.net/browse/JDK-8139150
>> http://cr.openjdk.java.net/~thartmann/8139150/webrev.00/
> 
> src/share/vm/classfile/stackMapTable.cpp
>     No comments.
> 
> Thumbs up!
> 
> Did a quick audit and I don't see any other calls to
> class_format_error() with the same issue.
> 
> This bug is very old. That ResourceMark came from here:
> 
> $ sp -r1.17 src/share/vm/classfile/stackMapTable.cpp
> src/share/vm/classfile/SCCS/s.stackMapTable.cpp:
> 
> D 1.17 05/06/20 17:21:50 mingyao 18 17  00015/00008/00446
> MRs:
> COMMENTS:
> Fixed 6275215, VM fails on StackMapTable jcod tests (VerifyError)
> Fixed 6275199, VM fails on StackMapTable jcod tests
> Fixed 6275153, VM fails on StackMapTable tests
> 
> And the code looked like this:
> 
> 187a185,194
>>     if (offset >= _code_length ||
>>         _code_data[offset] != ClassVerifier::NEW_OFFSET) {
>>       ResourceMark rm(THREAD);
>>       Exceptions::fthrow(
>>         THREAD_AND_LOCATION,
>>         vmSymbolHandles::java_lang_ClassFormatError(),
>>         "StackMapTable format error: bad offset for Uninitialized"
>>       );
>>       return NULL;
>>     }
> 
> 
> The class_format_error() call came from here:
> 
> D 1.21 06/04/13 11:43:50 km88527 23 22  00064/00108/00360
> MRs:
> COMMENTS:
> fixed 6402717: Error verifying java.lang.Error causes VM to exit silently due to stack overflow
> 
> and the code changed to look like this:
> 
>     if (offset >= _code_length ||
>         _code_data[offset] != ClassVerifier::NEW_OFFSET) {
>       ResourceMark rm(THREAD);
>       _verifier->class_format_error(
>         "StackMapTable format error: bad offset for Uninitialized");
>       return NULL;
>     }

Thanks for tracking this down. Seems like the old fix forgot to remove the ResourceMark and for some reason this never showed up.

> This fix should probably be backported... but I would
> check with Harold...

Yes, I think so too.

Thanks,
Tobias

> 
> Dan
> 
> 
>>
>> Problem:
>> If class verification fails in StackMapReader::parse_verification_type(), ClassVerifier::class_format_error() is invoked to pass the error message. The method allocates a new string and saves it in ClassVerifier::_message. The problem is that the caller creates a new ResourceMark that leads to _message being deallocated after return. However, later in Verifier::verify() we call ClassVerifier::exception_message() to get the message and pass it on.
>>
>> Solution:
>> We should not create a ResourceMark here. There is a top level ResourceMark in Verifier::verify() that will take care of freeing the memory allocated in ClassVerifier::class_format_error().
>>
>> Tested with JPRT and the failing testcase.
>>
>> Thanks,
>> Tobias
>