I have previously seen a number of libertarian sources (e.g. this blog) convincingly argue that imposing second-hand smoke danger on others constitutes a violation of non-aggression principle and therefore banning smoking is a valid libertarian approach.
It may be a bit murky in regards to people who have a choice to not be near a smoker, e.g. a patron of a private business who can choose to take their business elsewhere - in which case the freedom of smokers and of business owner may outweigh the non-smoker's freedom. But it seems much more clear-cut in regards to people who do NOT have such an easy choice; for example employees of smoking-OK restaurant; or neighbours of smoking-OK building; or people visiting public spaces.
As such, a government action to ban smoking can be argued to be a legitimate libertarian approach, as defense of victims who suffer from someone violating non-aggression principle - including in private businesses for the sake of their employees.
(you can think of it, for simile's sake, in terms of "is the government allowed to ban hitting you with a stick?").