Merge branch 'fix-impersonation-issue' into 'master'

Prevent privilege escalation via "impersonate" feature

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/15548

See merge request !1956

app/controllers/admin/application_controller.rb

@@ -6,12 +6,6 @@ class Admin::ApplicationController < ApplicationController
   layout 'admin'
 
   def authenticate_admin!
-    return render_404 unless current_user.is_admin?
-  end
-
-  def authorize_impersonator!
-    if session[:impersonator_id]
-      User.find_by!(username: session[:impersonator_id]).admin?
-    end
+    render_404 unless current_user.is_admin?
   end
 end

app/controllers/admin/impersonation_controller.rb

-class Admin::ImpersonationController < Admin::ApplicationController
-  skip_before_action :authenticate_admin!, only: :destroy
-
-  before_action :user
-  before_action :authorize_impersonator!
-
-  def create
-    session[:impersonator_id] = current_user.username
-    session[:impersonator_return_to] = request.env['HTTP_REFERER']
-
-    warden.set_user(user, scope: 'user')
-
-    flash[:alert] = "You are impersonating #{user.username}."
-
-    redirect_to root_path
-  end
-
-  def destroy
-    redirect = session[:impersonator_return_to]
-
-    warden.set_user(user, scope: 'user')
-
-    session[:impersonator_return_to] = nil
-    session[:impersonator_id] = nil
-
-    redirect_to redirect || root_path
-  end
-
-  def user
-    @user ||= User.find_by!(username: params[:id] || session[:impersonator_id])
-  end
-end

app/controllers/admin/impersonations_controller.rb

+class Admin::ImpersonationsController < Admin::ApplicationController
+  skip_before_action :authenticate_admin!
+  before_action :authenticate_impersonator!
+
+  def destroy
+    original_user = current_user
+
+    warden.set_user(impersonator, scope: :user)
+
+    session[:impersonator_id] = nil
+
+    redirect_to admin_user_path(original_user)
+  end
+
+  private
+
+  def impersonator
+    @impersonator ||= User.find(session[:impersonator_id]) if session[:impersonator_id]
+  end
+
+  def authenticate_impersonator!
+    render_404 unless impersonator && impersonator.is_admin? && !impersonator.blocked?
+  end
+end

app/controllers/admin/users_controller.rb

@@ -31,6 +31,22 @@ class Admin::UsersController < Admin::ApplicationController
     user
   end
 
+  def impersonate
+    if user.blocked?
+      flash[:alert] = "You cannot impersonate a blocked user"
+
+      redirect_to admin_user_path(user)
+    else
+      session[:impersonator_id] = current_user.id
+
+      warden.set_user(user, scope: :user)
+
+      flash[:alert] = "You are now impersonating #{user.username}"
+
+      redirect_to root_path
+    end
+  end
+
   def block
     if user.block
       redirect_back_or_admin_user(notice: "Successfully blocked")

app/views/layouts/header/_default.html.haml

@@ -15,7 +15,7 @@
               = icon('search')
           - if session[:impersonator_id]
             %li.impersonation
-              = link_to stop_impersonation_admin_users_path, method: :delete, title: 'Stop impersonation', data: { toggle: 'tooltip', placement: 'bottom' } do
+              = link_to admin_impersonation_path, method: :delete, title: 'Stop impersonation', data: { toggle: 'tooltip', placement: 'bottom' } do
                 = icon('user-secret fw')
           - if current_user.is_admin?
             %li

config/routes.rb

@@ -222,8 +222,6 @@ Gitlab::Application.routes.draw do
       resources :keys, only: [:show, :destroy]
       resources :identities, only: [:index, :edit, :update, :destroy]
 
-      delete 'stop_impersonation' => 'impersonation#destroy', on: :collection
-
       member do
         get :projects
         get :keys
@@ -233,12 +231,14 @@ Gitlab::Application.routes.draw do
         put :unblock
         put :unlock
         put :confirm
-        post 'impersonate' => 'impersonation#create'
+        post :impersonate
         patch :disable_two_factor
         delete 'remove/:email_id', action: 'remove_email', as: 'remove_email'
       end
     end
 
+    resource :impersonation, only: :destroy
+
     resources :abuse_reports, only: [:index, :destroy]
     resources :applications
 

spec/controllers/admin/impersonations_controller_spec.rb

+require 'spec_helper'
+
+describe Admin::ImpersonationsController do
+  let(:impersonator) { create(:admin) }
+  let(:user) { create(:user) }
+
+  describe "DELETE destroy" do
+    context "when not signed in" do
+      it "redirects to the sign in page" do
+        delete :destroy
+
+        expect(response).to redirect_to(new_user_session_path)
+      end
+    end
+
+    context "when signed in" do
+      before do
+        sign_in(user)
+      end
+
+      context "when not impersonating" do
+        it "responds with status 404" do
+          delete :destroy
+
+          expect(response.status).to eq(404)
+        end
+
+        it "doesn't sign us in" do
+          delete :destroy
+
+          expect(warden.user).to eq(user)
+        end
+      end
+
+      context "when impersonating" do
+        before do
+          session[:impersonator_id] = impersonator.id
+        end
+
+        context "when the impersonator is not admin (anymore)" do
+          before do
+            impersonator.admin = false
+            impersonator.save
+          end
+
+          it "responds with status 404" do
+            delete :destroy
+
+            expect(response.status).to eq(404)
+          end
+
+          it "doesn't sign us in as the impersonator" do
+            delete :destroy
+
+            expect(warden.user).to eq(user)
+          end
+        end
+
+        context "when the impersonator is admin" do
+          context "when the impersonator is blocked" do
+            before do
+              impersonator.block!
+            end
+
+            it "responds with status 404" do
+              delete :destroy
+
+              expect(response.status).to eq(404)
+            end
+
+            it "doesn't sign us in as the impersonator" do
+              delete :destroy
+
+              expect(warden.user).to eq(user)
+            end
+          end
+
+          context "when the impersonator is not blocked" do
+            it "redirects to the impersonated user's page" do
+              delete :destroy
+
+              expect(response).to redirect_to(admin_user_path(user))
+            end
+
+            it "signs us in as the impersonator" do
+              delete :destroy
+
+              expect(warden.user).to eq(impersonator)
+            end
+          end
+        end
+      end
+    end
+  end
+end

spec/controllers/admin/users_controller_spec.rb

 require 'spec_helper'
 
 describe Admin::UsersController do
-  let(:admin)    { create(:admin) }
+  let(:user) { create(:user) }
+  let(:admin) { create(:admin) }
 
   before do
     sign_in(admin)
@@ -104,4 +105,50 @@ describe Admin::UsersController do
       patch :disable_two_factor, id: user.to_param
     end
   end
+
+  describe "POST impersonate" do
+    context "when the user is blocked" do
+      before do
+        user.block!
+      end
+
+      it "shows a notice" do
+        post :impersonate, id: user.username
+
+        expect(flash[:alert]).to eq("You cannot impersonate a blocked user")
+      end
+
+      it "doesn't sign us in as the user" do
+        post :impersonate, id: user.username
+
+        expect(warden.user).to eq(admin)
+      end
+    end
+
+    context "when the user is not blocked" do
+      it "stores the impersonator in the session" do
+        post :impersonate, id: user.username
+
+        expect(session[:impersonator_id]).to eq(admin.id)
+      end
+
+      it "signs us in as the user" do
+        post :impersonate, id: user.username
+
+        expect(warden.user).to eq(user)
+      end
+
+      it "redirects to root" do
+        post :impersonate, id: user.username
+
+        expect(response).to redirect_to(root_path)
+      end
+
+      it "shows a notice" do
+        post :impersonate, id: user.username
+
+        expect(flash[:alert]).to eq("You are now impersonating #{user.username}")
+      end
+    end
+  end
 end