Ceiling white paint as a primer.
Can you use a ceiling white paint as a primer for the walls?
That depends on the kinds of paint that are in your jar, and on your wall.
Latex paint can be painted over with latex paint. Better not put a stronger paint (acrylics) over latex paint.
If your wall was painted with acrylics or oil based paint, you can use the primer.
I will have to offer a differing opinion to the previous answer.
I will recommend against using a finish as a primer. Primers are designed to adhere to a wide variety of surfaces. Finish paints should be applied to non-slick surfaces.