Who can give consent to search a vehicle?

If a cop "smells" marijuana, he already has authority to search the car based on probable cause, it's just easier to ask for permission. The cop has then legally detained the vehicle and everyone inside it, and for officer safety purposes may conduct a pat for weapons on everyone in the vehicle. If subsequent illegal narcotics are found through this pat, it is legal as long as he did not insert his hands into the pockets, unless given permission from the subject. Hope that helps.