How can I solve this git access rules: any one can create new branch, only admin can merge into "master"?

How can I solve this git access rules: any one can create new branch, only
admin can merge into "master"?

We are using git for our codes control, and I have some question on it.
I want this in a repo, using git it self or tools such as "gitolite": 1,
only specified persion can merge code to specified branch. 2, somebody(
such as a group called "admin") can create new branch, and have full
permission "RW+", maybe all development group menber should have this
access permission *3, all persion can create new branch with a specified
prefix, such as a prefix called "bug", will allow all persion create
branches called bug001, bug123...
I don't know if I missunderstanded the usage of "git", or maybe I should
actualize this access rules via "repo", not branch?
Look forward to someone can answer my question eagerly, any solution will
be ok, such as gitolite, Thanks!