Fix an information disclosure when requesting access to a group containing private projects

The issue was with the `User#groups` and `User#projects` associations
which goes through the `User#group_members` and `User#project_members`.

Initially I chose to use a secure approach by storing the requester's
user ID in `Member#created_by_id` instead of `Member#user_id` because I
was aware that there was a security risk since I didn't know the
codebase well enough.

Then during the review, we decided to change that and directly store the
requester's user ID into `Member#user_id` (for the sake of simplifying
the code I believe), meaning that every `group_members` / `project_members`
association would include the requesters by default...

My bad for not checking that all the `group_members` / `project_members`
associations and the ones that go through them (e.g. `Group#users` and
`Project#users`) were made safe with the `where(requested_at: nil)` /
`where(members: { requested_at: nil })` scopes.

Now they are all secure.
Signed-off-by: Rémy Coutable <remy@rymai.me>

app/controllers/dashboard/groups_controller.rb

 class Dashboard::GroupsController < Dashboard::ApplicationController
   def index
-    @group_members = current_user.group_members.page(params[:page])
+    @group_members = current_user.group_members.includes(:source).page(params[:page])
   end
 end

app/models/group.rb

@@ -11,7 +11,7 @@ class Group < Namespace
   has_many :users, -> { where(members: { requested_at: nil }) }, through: :group_members
 
   has_many :owners,
-    -> { where(members: { access_level: Gitlab::Access::OWNER }) },
+    -> { where(members: { requested_at: nil, access_level: Gitlab::Access::OWNER }) },
     through: :group_members,
     source: :user
 

app/models/user.rb

@@ -57,7 +57,7 @@ class User < ActiveRecord::Base
 
   # Groups
   has_many :members, dependent: :destroy
-  has_many :group_members, dependent: :destroy, source: 'GroupMember'
+  has_many :group_members, -> { where(requested_at: nil) }, dependent: :destroy, source: 'GroupMember'
   has_many :groups, through: :group_members
   has_many :owned_groups, -> { where members: { access_level: Gitlab::Access::OWNER } }, through: :group_members, source: :group
   has_many :masters_groups, -> { where members: { access_level: Gitlab::Access::MASTER } }, through: :group_members, source: :group
@@ -65,7 +65,7 @@ class User < ActiveRecord::Base
   # Projects
   has_many :groups_projects,          through: :groups, source: :projects
   has_many :personal_projects,        through: :namespace, source: :projects
-  has_many :project_members,          dependent: :destroy, class_name: 'ProjectMember'
+  has_many :project_members, -> { where(requested_at: nil) }, dependent: :destroy, class_name: 'ProjectMember'
   has_many :projects,                 through: :project_members
   has_many :created_projects,         foreign_key: :creator_id, class_name: 'Project'
   has_many :users_star_projects, dependent: :destroy

app/views/admin/users/groups.html.haml

 - page_title "Groups", @user.name, "Users"
 = render 'admin/users/head'
 
-- if @user.group_members.present?
+- group_members = @user.group_members.includes(:source)
+- if group_members.any?
   .panel.panel-default
     .panel-heading Groups:
     %ul.well-list
-      - @user.group_members.each do |group_member|
+      - group_members.each do |group_member|
         - group = group_member.group
         %li.group_member
           %span{class: ("list-item-name" unless group_member.owner?)}

spec/features/groups/members/user_requests_access_spec.rb

@@ -4,6 +4,7 @@ feature 'Groups > Members > User requests access', feature: true do
   let(:user) { create(:user) }
   let(:owner) { create(:user) }
   let(:group) { create(:group, :public) }
+  let!(:project) { create(:project, :private, namespace: group) }
 
   background do
     group.add_owner(owner)
@@ -24,6 +25,20 @@ feature 'Groups > Members > User requests access', feature: true do
     expect(page).not_to have_content 'Leave Group'
   end
 
+  scenario 'user does not see private projects' do
+    perform_enqueued_jobs { click_link 'Request Access' }
+
+    expect(page).not_to have_content project.name
+  end
+
+  scenario 'user does not see group in the Dashboard > Groups page' do
+    perform_enqueued_jobs { click_link 'Request Access' }
+
+    visit dashboard_groups_path
+
+    expect(page).not_to have_content group.name
+  end
+
   scenario 'user is not listed in the group members page' do
     click_link 'Request Access'
 

spec/models/user_spec.rb

@@ -31,6 +31,26 @@ describe User, models: true do
     it { is_expected.to have_many(:spam_logs).dependent(:destroy) }
     it { is_expected.to have_many(:todos).dependent(:destroy) }
     it { is_expected.to have_many(:award_emoji).dependent(:destroy) }
+
+    describe '#group_members' do
+      it 'does not include group memberships for which user is a requester' do
+        user = create(:user)
+        group = create(:group, :public)
+        group.request_access(user)
+
+        expect(user.group_members).to be_empty
+      end
+    end
+
+    describe '#project_members' do
+      it 'does not include project memberships for which user is a requester' do
+        user = create(:user)
+        project = create(:project, :public)
+        project.request_access(user)
+
+        expect(user.project_members).to be_empty
+      end
+    end
   end
 
   describe 'validations' do