On 4/15/20 12:26 pm, Anton Litvinov wrote:
When JDK is used in a normal way and not as it is used in the reproducer, "opposite" is always HWND of a peer of "java.awt.Window" instance, thus for
such cases there is no need to search for some parent HWND of the "opposite" HWND. I do not want to break behavior of JDK for these normal scenarios, by
getting some parent HWND of the valid "opposite" HWND. I do not want to rely on expectation that for valid "opposite" HWND the method
"AwtComponent::GetTopLevelParentForWindow" must return the same "opposite" HWND, I do not want to rely on this expectation and run the risk of using
some incorrect HWND as opposite, when there was already valid "opposite" HWND in hands, and by this to break existing JDK behavior related to focus handling,
because this edited "AwtWindow::SendWindowEvent" method is really involved in focus handling.
That was the question, when GetTopLevelParentForWindow may return
wrong/incorrect HWND and why the same situation may not happen after fix when
we call GetTopLevelParentForWindow later.
Thank you,
Anton
On 15/04/2020 07:56, Sergey Bylokhov wrote:
On 4/14/20 11:12 am, Anton Litvinov wrote:
I think that it is better not to change current well established old behavior in the method "AwtWindow::SendWindowEvent(jint, HWND, jint,
jint)" - what is first to get "jobject" from the original "opposite" HWND and try to use it for construction of
"TimedWindowEvent". I was trying to make a fix which will just extend the code and will address just this very unreal and very narrow
scenario without running the risk of affecting or breaking wide range of other normal scenarios under which this code was working well from the
moment of its creation. If we assign parent HWND to the "opposite" from the very beginning, then we will change the currently existing
behavior in favor of addressing this almost unreal bug and may for some cases, which we do not know yet, start using parent HWND instead of a valid
original "opposite" HWND whose target will be instance of "java.awt.Window".
In my opinion it is better not to omit first attempt to use original "opposite" with
related to it "jobject" instance.
If it is not safe to replace the opposite by the GetTopLevelParentForWindow(1)
in the first place then
why it is safe to use it in the fix later(1)? What could go wrong at step (1)
and why it will work fine
at step(2)?
Thank you,
Anton
On 14/04/2020 16:41, Sergey Bylokhov wrote:
Hi, Anton.
Probably it is possible to simplify the code a little bit:
Can we just replace initial "opposite" by the top level HWND?
+ opposite = AwtComponent::GetTopLevelParentForWindow(opposite);
AwtComponent *awtOpposite = AwtComponent::GetComponent(opposite);
and add only one check
jOpposite = awtOpposite->GetTarget(env);
+ if ((jOpposite != NULL) &&
+ !env->IsInstanceOf(jOpposite, windowCls)) {
+ env->DeleteLocalRef(jOpposite);
+ jOpposite = NULL;
+ }
On 4/10/20 1:32 pm, Anton Litvinov wrote:
Hello,
Could you please review the following fix for the bug.
Bug: https://bugs.openjdk.java.net/browse/JDK-8242498
Webrev: http://cr.openjdk.java.net/~alitvinov/8242498/jdk15/webrev.00
The bug is the JVM crash, which occurs because a not existing method is called
on a Java object which is not an instance of the expected Java class that has
such a method. Such discrepancy of the expected type and the type in runtime is
possible, because the Java object, whose field value is set to the instance of
the not expected Java class, is instantiated by AWT native code through JNI
invocation. Since JNI does not validate arguments passed to Java class
constructor and since AWT native code does not validate arguments prior to
invoking Java class constructor through JNI, such invalid object is created.
REASON OF THE CRASH:
The fact that in the method "java.awt.DefaultKeyboardFocusManager.dispatchEvent(AWTEvent)" in the case "WindowEvent.WINDOW_LOST_FOCUS" of switch operator the variable
defined by the expression "Window oppositeWindow = we.getOppositeWindow();" in runtime is instance of "java.awt.Component" class instead of "java.awt.Window"
class. The crash occurs during attempt to call the method "java.awt.Window.getTemporaryLostComponent()" on the object "oppositeWindow" which in runtime is
"Component" instead of the expected "Window" object, and since the method "getTemporaryLostComponent()" does not exist in "java.awt.Component" class
JVM cannot find this method and initiates the crash.
ROOT CAUSE OF THE BUG:
Transfer of the object of the incompatible type "java.awt.Component" instead of an object of "java.awt.Window" type as "opposite" argument
to the constructor "TimedWindowEvent(Window source, int id, Window opposite, int oldState, int newState, long time)" of the class
"sun.awt.TimedWindowEvent" through JNI invocation. This JNI invocation occurs in the C++ class method "AwtWindow::SendWindowEvent(jint, HWND, jint,
jint)" in the file "src/java.desktop/windows/native/libawt/windows/awt_Window.cpp". The exact expression creating the instance of Java class
"TimedWindowEvent" with the invalid value of the field "opposite" is following:
jobject event = env->NewObject(wClassEvent, wEventInitMID, target, id,
jOpposite, oldState, newState, ::JVM_CurrentTimeMillis(NULL, 0));
THE FIX:
The fix changes "AwtWindow::SendWindowEvent(jint, HWND, jint, jint)" method in the file "awt_Window.cpp" to introduce the code
which verifies that the Java object "jOpposite" is really instance of the class "java.awt.Window", and if it is not then the fix
tries to get Java object corresponding to parent window of the original "opposite" HWND. And if this parent window object also is not
instance of "java.awt.Window" class, then NULL value is passed to the constructor of "TimedWindowEvent" class.
Thank you,
Anton
--
Best regards, Sergey.
