static inline void vmsvga_update_rect_flush(struct vmsvga_state_s *s)
{
    struct vmsvga_rect_s *rect;

    if (s->invalidated) {
        s->redraw_fifo_first = s->redraw_fifo_last;
        return;
    }
    /* Overlapping region updates can be optimised out here - if someone
     * knows a smart algorithm to do that, please share.  */
    while (s->redraw_fifo_first != s->redraw_fifo_last) {
        rect = &s->redraw_fifo[s->redraw_fifo_first++];
        s->redraw_fifo_first &= REDRAW_FIFO_LEN - 1;
        vmsvga_update_rect(s, rect->x, rect->y, rect->w, rect->h);
    }
}

The product writes data past the end, or before the beginning, of the intended buffer.