<AWT Dev> [15] Review request for 8242498: Invalid "sun.awt.TimedWindowEvent" object leads to JVM crash

Anton Litvinov anton.litvinov at oracle.com
Fri Apr 10 20:32:46 UTC 2020


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.

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.

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 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,

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