How long should a brief CV for a call for papers be?
If it is more than a page it is too long. As for what should be there, say something about your education, current employment and some of your publications. It isn't necessary to be comprehensive but include things that are most relevant to the conference and to the paper you are submitting. 

That is probably about enough, but if it seems too short, include honors, etc. if you like. 

All the committee is looking for at this point is that you are qualified to say what you want to say in the resulting paper. Focus on that above all.