Obtain lease before querying LDAP

app/controllers/application_controller.rb

@@ -246,6 +246,8 @@ class ApplicationController < ActionController::Base
 
   def ldap_security_check
     if current_user && current_user.requires_ldap_check?
+      return unless current_user.try_obtain_ldap_lease
+
       unless Gitlab::LDAP::Access.allowed?(current_user)
         sign_out current_user
         flash[:alert] = "Access denied for your LDAP account."

app/models/user.rb

@@ -603,6 +603,13 @@ class User < ActiveRecord::Base
     end
   end
 
+  def try_obtain_ldap_lease
+    # After obtaining this lease LDAP checks will be blocked for 600 seconds
+    # (10 minutes) for this user.
+    lease = Gitlab::ExclusiveLease.new("user_ldap_check:#{id}", timeout: 600)
+    lease.try_obtain
+  end
+
   def solo_owned_groups
     @solo_owned_groups ||= owned_groups.select do |group|
       group.owners == [self]

lib/gitlab/user_access.rb

@@ -3,7 +3,7 @@ module Gitlab
     def self.allowed?(user)
       return false if user.blocked?
 
-      if user.requires_ldap_check?
+      if user.requires_ldap_check? && user.try_obtain_ldap_lease
         return false unless Gitlab::LDAP::Access.allowed?(user)
       end