[9] RFR(S): Crash with assert: symbol conversion failure in java_lang_String::create_from_symbol()

Tobias Hartmann tobias.hartmann at oracle.com
Mon Sep 19 09:21:14 UTC 2016

Hi David,

On 19.09.2016 10:30, David Holmes wrote:
> On 19/09/2016 6:09 PM, Tobias Hartmann wrote:
>> Coleen, David, thanks for the reviews and sorry for the delay!
>> I agree that we should validate the Strings we get through JNI, but the code in create_from_str() and create_from_symbol() was originally added to check the result of String compression with the Compact Strings feature and not to check for valid UTF-8.
>> I think UTF-8 validity should be checked earlier (before or during Symbol creation) and this affects other JNI methods that take C-Strings as well (jni_NewString, jni_NewStringUTF, jni_DefineClass, ...). This is a general problem with JNI not validating input Strings.
>> Are you fine with pushing the proposed fix (webrev.00) and open a follow up bug to fix JNI (and potentially re-enable the Compact Strings asserts because their existence is still justified)?
> As I wrote in the bug report:
> "I don't think I agree with the removed checks in either case. JNI doesn't do argument checking and so doesn't detect the invalid UTF-8 string. But the VM expects to work with valid strings. It seems quite reasonable to me that the VM should validate the UTF-8 and report some kind of failure to make these invalid inputs visible. Otherwise the bad JNI codes goes undetected. Maybe an assertion is too strong, perhaps we should throw InternalError? "

Yes, I've seen that and, as I said, I agree that we should validate the Strings.

> If the VM does not detect this and respond to it exactly what happens with the bad UTF-8 string?

In the FindClass case, we just return NULL. I don't know if there are potential problems with invalid UTF-8 strings at other places in the code.

> JNI doesn't do input validation - it is a "feature" of JNI so not to penalize correct code. 

Right, but this check only affects debug builds.

> If the test that triggered this is sending in bad UTF-8 because it expects JNI to do validation then it is an invalid test. I think the asserts serve their purpose exactly - to show where invalid inputs came from. If this was bad user code then it would be up to them to fix it. If it is a bad test then the test should be fixed.

Sure, the test is broken and will be fixed. So you're suggesting to leave the check in create_from_symbol() as it is and re-enable the check in create_from_str()?

I'm fine with that but as I remember, re-enabling the check in create_from_str() causes other test failures.

Best regards,

> Sorry.
> David
>> Thanks,
>> Tobias
>> On 12.09.2016 02:47, David Holmes wrote:
>>> On 10/09/2016 6:55 AM, Coleen Phillimore wrote:
>>>> This change is fine because it matches the commented out assert in
>>>> create_from_str().   We should probably figure out what it would take to
>>>> check the characters coming in from JNI and decide whether we should do
>>>> this.  If not, it doesn't make sense to have commented out asserts.
>>>> But this is okay for jdk9.
>>> Grumble, grumble ... both are bad. If the VM doesn't validate this bad UTF-8 then where does it go? And how does the generator of the bad UTF-8 get informed? An assert may be too drastic but can we throw an exception (InternalError?) ?
>>> David
>>>> Thanks,
>>>> Coleen
>>>> On 9/9/16 8:42 AM, Tobias Hartmann wrote:
>>>>> Hi,
>>>>> please review the following patch:
>>>>> https://bugs.openjdk.java.net/browse/JDK-8164561
>>>>> http://cr.openjdk.java.net/~thartmann/8164561/webrev.00/
>>>>> The verification code in java_lang_String::create_from_symbol() that
>>>>> was added by Compact Strings fails because the input symbol does not
>>>>> contain valid UTF8. The problem is that a JCK JNI test passes an
>>>>> invalid UTF8 string as class name to the JNI method "FindClass". In
>>>>> fact, the string contains garbage from reading past array boundaries
>>>>> because of a bug in the test [1]. The JNI spec [2] states that 'name'
>>>>> should be "a fully-qualified class name (that is, a package name,
>>>>> delimited by “/”, followed by the class name). If the name begins with
>>>>> “[“ (the array signature character), it returns an array class. The
>>>>> string is encoded in modified UTF-8".
>>>>> I nevertheless think that we should not crash in the case of an
>>>>> invalid UTF8 string and therefore disabled the verification code with
>>>>> a comment. We did the same for java_lang_String::create_from_str() [3].
>>>>> Tested with failing JCK test and JPRT (running).
>>>>> Thanks,
>>>>> Tobias
>>>>> [1] https://bugs.openjdk.java.net/browse/JCK-7307244
>>>>> [2]
>>>>> https://docs.oracle.com/javase/8/docs/technotes/guides/jni/spec/functions.html#FindClass
>>>>> [3]
>>>>> http://hg.openjdk.java.net/jdk9/hs/hotspot/file/d060826d0911/src/share/vm/classfile/javaClasses.cpp#l274

More information about the hotspot-dev mailing list