Kernel crash via overflowing framebuffer timing product

Divide-by-zero in Linux framebuffer monitor code allows local users to crash affected kernels through crafted video-mode totals. fb_videomode_from_videomode() multiplies horizontal and vertical totals without checking whether the product overflows to zero, then uses that zero product as the divisor in its refresh-rate calculation. Triggering the fault requires local low-privileged access to a path that supplies framebuffer timings, and the bounded impact is a kernel crash.