<AWT Dev>  Review request for 8242498: Invalid "sun.awt.TimedWindowEvent" object leads to JVM crash
anton.litvinov at oracle.com
Fri Apr 10 20:32:46 UTC 2020
Could you please review the following fix for the bug.
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
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
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