This is probably a very basic solution. I've got roof leak, and its in a space of wide open shingles. I.e., not a valley, flashing, or window issue - where most problems occur (and about which most posts ask).
The leak is minor, showing itself in the attic as a spot of moist roof sheathing. No drip to attic floor yet.
What's my fix for this? Do I have to remove shingles, or can I spread some tar up there? Roof is traditional asphalt shingles.
As Tom said, you need to make sure of where the leak is coming in from. What you are seeing in the attic could very well be a few feet away from where the water is actually entering.
The most permanent and best fix is to replace the shingle. Not very hard to do. If you don't have extra shingles laying around and would rather cement it, you could do that to but it is not as permanent of a fix.