Compile and run this bit of code:

QPixmap testPixmap (10,10);
QImage testImage2(1,10, QImage::Format_RGB32);
testPixmap.convertFromImage( testImage2 );

The code creates a 10x10 pixmap, and then re-initiaizes the pixmap by converting an image of 1x10.

This causes a buffer overrun in QMacPixmapData::macCreatePixels, in this line:

if (pixels)
    memcpy(base_pixels, pixels, pixelsSize);

The reason is that the target of the memcopy has been allocated like this:

base_pixels = static_cast<quint32 *>(malloc(numBytes));

where numBytes is 160. However, pixelsSize is still the old size (480 in this case), causing 480 bytes to be copied into a 160 byte memory region.

If you're lucky, this results in a 'EXC_BAD_ACCESS' on osx, if not your program runs with its data corrupted.