There is a company that makes what looks like little plastic thumb tacks with barbs on the tip. They come in colors or clear. I've seen them in several different parts stores. Sorry, don't remember the brand.
The proper reair is to replace the headliner. What has happened is the foam underlayment, which the cloth headliner is glued to, has dried out. Just trying to glue the cloth back up won't work as you are glueing it to dry foam (which will soon be dust). The push in/screw in buttons can be picked up at AutoZone or a similiar store. They will punch holes in the cloth, foam, and cardboard backing. If the car is not worth a replacement headliner, use the buttons. If the car is more than basic transportation, get a new headliner.
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