qt: QSharedMemory class created shared memory segments with insecure permissions

The QSharedMemory class in Qt 5.0.0, 4.8.x before 4.8.5, 4.7.x before 4.7.6, and other versions including 4.4.0 uses weak permissions world-readable and world-writable for shared memory segments, which allows local users to read sensitive information or modify critical program data, as demonstrat...