RFR: JDK-8245432: Lookup::defineHiddenClass should throw UnsupportedClassVersionError if the given bytes are of an unsupported major or minor version

[Johannes Kuhn]

Thanks.

Noted that readInt can read outside of the byte array when it is shorter 
than 4 bytes, throwing an ArrayIndexOutOfBoundsException.
Same applies for readUnsignedShort.

Test cases for malformedClassFiles:

new byte[3], new byte[] {0xCA, 0xFE, 0xBA, 0xBE, 0x00}


- Johannes


On 29-May-20 21:23, Mandy Chung wrote:
> It's fixed.  Thanks
> Mandy
>
> On 5/28/20 4:35 PM, Johannes Kuhn wrote:
>> Hi,
>>
>> just noticed a small thing:
>> The magic is 4 bytes, but readUnsignedShort reads two bytes.
>>
>> - Johannes
>>
>> On 28-May-20 19:25, Mandy Chung wrote:
>>>
>>>
>>> On 5/28/20 6:55 AM, Alan Bateman wrote:
>>>> On 28/05/2020 05:13, Mandy Chung wrote:
>>>>> Updated webrev:
>>>>> http://cr.openjdk.java.net/~mchung/jdk15/webrevs/8245432/webrev.01/
>>>>>
>>>>> I modify this patch to check the class file version and throws CFE 
>>>>> if unsupported before creating ClassReader. This also fixes 
>>>>> JDK-8245061 that it reads the value of `this_class` as a constant 
>>>>> (as ASM will throw an exception if it's not a constant) and also 
>>>>> ensures that `this_class` is a CONSTANT_Class_info by checking the 
>>>>> descriptor string from Type.
>>>> I don't want to complicate this further but the --enable-preview 
>>>> handling in the VM doesn't seem to expose an internal property that 
>>>> allows code in the libraries know if preview feature are enabled or 
>>>> not. I was assuming that isSupportedClassFileVersion would need to 
>>>> check that.
>>>>
>>>
>>> The runtime will ensure if --enable-preview is set if a class file 
>>> with minor is loaded.   I will prefer to keep 
>>> VM::isSupportedClassFileVersion to validate the given major/minor 
>>> version.  At runtime, it will fail when such class file is loaded if 
>>> preview is not enabled.
>>>
>>> I'll add a comment to describe that.
>>>
>>>> Will readUnsignedShort throw AIOBE if the offset is beyond the length? 
>>>
>>> Good catch.  I add the check to throw CFE.
>>> +            private static int readUnsignedShort(byte[] bytes, int 
>>> offset) {
>>> +                if (offset >= bytes.length) {
>>> +                    throw new ClassFormatError("Invalid ClassFile 
>>> structure");
>>> +                }
>>> +                return ((bytes[offset] & 0xFF) << 8) | 
>>> (bytes[offset + 1] & 0xFF);
>>> +            }
>>>
>>>> Also are you sure about "& 0xCAFEBABE", I assumed it would just 
>>>> check the magic number is equal to that.
>>>
>>> It should check ==.  Fixed.
>>>
>>> thanks
>>> Mandy
>>
>>
>