Restrict user profiles based on restricted visibility levels

app/controllers/users_controller.rb

 class UsersController < ApplicationController
   skip_before_action :authenticate_user!
   before_action :set_user
+  before_filter :authorize_read_user, only: [:show]
 
   def show
     respond_to do |format|
@@ -74,6 +75,9 @@ class UsersController < ApplicationController
   end
 
   private
+  def authorize_read_user
+    render_404 unless @user.public?
+  end
 
   def set_user
     @user = User.find_by_username!(params[:username])

app/models/user.rb

@@ -835,6 +835,10 @@ class User < ActiveRecord::Base
     notification_settings.find_or_initialize_by(source: source)
   end
 
+  def public?
+    current_application_settings.restricted_visibility_levels.include?(Gitlab::VisibilityLevel::PUBLIC)
+  end
+
   private
 
   def projects_union