Prevent comments by email when issue is locked

This changes the permission check so it uses the policy on Noteable
instead of Project. This prevents bypassing of rules defined in
Noteable for locked discussions and confidential issues.

Also rechecks permissions when reply_to_discussion_id is provided since the
discussion_id may be from a different noteable.

app/policies/issue_policy.rb

@@ -18,6 +18,7 @@ class IssuePolicy < IssuablePolicy
     prevent :read_issue_iid
     prevent :update_issue
     prevent :admin_issue
+    prevent :create_note
   end
 
   rule { locked }.policy do

app/policies/personal_snippet_policy.rb

@@ -28,5 +28,8 @@ class PersonalSnippetPolicy < BasePolicy
 
   rule { anonymous }.prevent :comment_personal_snippet
 
-  rule { can?(:comment_personal_snippet) }.enable :award_emoji
+  rule { can?(:comment_personal_snippet) }.policy do
+    enable :create_note
+    enable :award_emoji
+  end
 end

app/policies/project_snippet_policy.rb

@@ -43,4 +43,6 @@ class ProjectSnippetPolicy < BasePolicy
     enable :update_project_snippet
     enable :admin_project_snippet
   end
+
+  rule { ~can?(:read_project_snippet) }.prevent :create_note
 end

app/services/notes/build_service.rb

@@ -9,7 +9,7 @@ module Notes
       if in_reply_to_discussion_id.present?
         discussion = find_discussion(in_reply_to_discussion_id)
 
-        unless discussion
+        unless discussion && can?(current_user, :create_note, discussion.noteable)
           note = Note.new
           note.errors.add(:base, 'Discussion to reply to cannot be found')
           return note
@@ -34,19 +34,8 @@ module Notes
       if project
         project.notes.find_discussion(discussion_id)
       else
-        discussion = Note.find_discussion(discussion_id)
-        noteable = discussion.noteable
-
-        return nil unless noteable_without_project?(noteable)
-
-        discussion
-      end
+        Note.find_discussion(discussion_id)
       end
-
-    def noteable_without_project?(noteable)
-      return true if noteable.is_a?(PersonalSnippet) && can?(current_user, :comment_personal_snippet, noteable)
-
-      false
     end
   end
 end

changelogs/unreleased/security-2779-fix-email-comment-permissions-check.yml

+---
+title: Prevent unauthorized replies when discussion is locked or confidential
+merge_request:
+author:
+type: security

lib/gitlab/email/handler/reply_processing.rb

@@ -56,7 +56,7 @@ module Gitlab
             raise ProjectNotFound unless author.can?(:read_project, project)
           end
 
-          raise UserNotAuthorizedError unless author.can?(permission, project || noteable)
+          raise UserNotAuthorizedError unless author.can?(permission, try(:noteable) || project)
         end
 
         def verify_record!(record:, invalid_exception:, record_name:)

spec/lib/gitlab/email/handler/create_note_handler_spec.rb

@@ -118,6 +118,43 @@ describe Gitlab::Email::Handler::CreateNoteHandler do
     end
   end
 
+  shared_examples "checks permissions on noteable" do
+    context "when user has access" do
+      before do
+        project.add_reporter(user)
+      end
+
+      it "creates a comment" do
+        expect { receiver.execute }.to change { noteable.notes.count }.by(1)
+      end
+    end
+
+    context "when user does not have access" do
+      it "raises UserNotAuthorizedError" do
+        expect { receiver.execute }.to raise_error(Gitlab::Email::UserNotAuthorizedError)
+      end
+    end
+  end
+
+  context "when discussion is locked" do
+    before do
+      noteable.update_attribute(:discussion_locked, true)
+    end
+
+    it_behaves_like "checks permissions on noteable"
+  end
+
+  context "when issue is confidential" do
+    let(:issue) { create(:issue, project: project) }
+    let(:note) { create(:note, noteable: issue, project: project) }
+
+    before do
+      issue.update_attribute(:confidential, true)
+    end
+
+    it_behaves_like "checks permissions on noteable"
+  end
+
   context "when everything is fine" do
     before do
       setup_attachment

spec/models/sent_notification_spec.rb

@@ -48,7 +48,7 @@ describe SentNotification do
     let(:note) { create(:diff_note_on_merge_request) }
 
     it 'creates a new SentNotification' do
-      expect { described_class.record_note(note, user.id) }.to change { described_class.count }.by(1)
+      expect { described_class.record_note(note, note.author.id) }.to change { described_class.count }.by(1)
     end
   end
 

spec/policies/personal_snippet_policy_spec.rb

@@ -14,6 +14,13 @@ describe PersonalSnippetPolicy do
     ]
   end
 
+  let(:comment_permissions) do
+    [
+      :comment_personal_snippet,
+      :create_note
+    ]
+  end
+
   def permissions(user)
     described_class.new(user, snippet)
   end
@@ -26,7 +33,7 @@ describe PersonalSnippetPolicy do
 
       it do
         is_expected.to be_allowed(:read_personal_snippet)
-        is_expected.to be_disallowed(:comment_personal_snippet)
+        is_expected.to be_disallowed(*comment_permissions)
         is_expected.to be_disallowed(:award_emoji)
         is_expected.to be_disallowed(*author_permissions)
       end
@@ -37,7 +44,7 @@ describe PersonalSnippetPolicy do
 
       it do
         is_expected.to be_allowed(:read_personal_snippet)
-        is_expected.to be_allowed(:comment_personal_snippet)
+        is_expected.to be_allowed(*comment_permissions)
         is_expected.to be_allowed(:award_emoji)
         is_expected.to be_disallowed(*author_permissions)
       end
@@ -48,7 +55,7 @@ describe PersonalSnippetPolicy do
 
       it do
         is_expected.to be_allowed(:read_personal_snippet)
-        is_expected.to be_allowed(:comment_personal_snippet)
+        is_expected.to be_allowed(*comment_permissions)
         is_expected.to be_allowed(:award_emoji)
         is_expected.to be_allowed(*author_permissions)
       end
@@ -63,7 +70,7 @@ describe PersonalSnippetPolicy do
 
       it do
         is_expected.to be_disallowed(:read_personal_snippet)
-        is_expected.to be_disallowed(:comment_personal_snippet)
+        is_expected.to be_disallowed(*comment_permissions)
         is_expected.to be_disallowed(:award_emoji)
         is_expected.to be_disallowed(*author_permissions)
       end
@@ -74,7 +81,7 @@ describe PersonalSnippetPolicy do
 
       it do
         is_expected.to be_allowed(:read_personal_snippet)
-        is_expected.to be_allowed(:comment_personal_snippet)
+        is_expected.to be_allowed(*comment_permissions)
         is_expected.to be_allowed(:award_emoji)
         is_expected.to be_disallowed(*author_permissions)
       end
@@ -85,7 +92,7 @@ describe PersonalSnippetPolicy do
 
       it do
         is_expected.to be_disallowed(:read_personal_snippet)
-        is_expected.to be_disallowed(:comment_personal_snippet)
+        is_expected.to be_disallowed(*comment_permissions)
         is_expected.to be_disallowed(:award_emoji)
         is_expected.to be_disallowed(*author_permissions)
       end
@@ -96,7 +103,7 @@ describe PersonalSnippetPolicy do
 
       it do
         is_expected.to be_allowed(:read_personal_snippet)
-        is_expected.to be_allowed(:comment_personal_snippet)
+        is_expected.to be_allowed(*comment_permissions)
         is_expected.to be_allowed(:award_emoji)
         is_expected.to be_allowed(*author_permissions)
       end
@@ -111,7 +118,7 @@ describe PersonalSnippetPolicy do
 
       it do
         is_expected.to be_disallowed(:read_personal_snippet)
-        is_expected.to be_disallowed(:comment_personal_snippet)
+        is_expected.to be_disallowed(*comment_permissions)
         is_expected.to be_disallowed(:award_emoji)
         is_expected.to be_disallowed(*author_permissions)
       end
@@ -122,7 +129,7 @@ describe PersonalSnippetPolicy do
 
       it do
         is_expected.to be_disallowed(:read_personal_snippet)
-        is_expected.to be_disallowed(:comment_personal_snippet)
+        is_expected.to be_disallowed(*comment_permissions)
         is_expected.to be_disallowed(:award_emoji)
         is_expected.to be_disallowed(*author_permissions)
       end
@@ -133,7 +140,7 @@ describe PersonalSnippetPolicy do
 
       it do
         is_expected.to be_disallowed(:read_personal_snippet)
-        is_expected.to be_disallowed(:comment_personal_snippet)
+        is_expected.to be_disallowed(*comment_permissions)
         is_expected.to be_disallowed(:award_emoji)
         is_expected.to be_disallowed(*author_permissions)
       end
@@ -144,7 +151,7 @@ describe PersonalSnippetPolicy do
 
       it do
         is_expected.to be_allowed(:read_personal_snippet)
-        is_expected.to be_allowed(:comment_personal_snippet)
+        is_expected.to be_allowed(*comment_permissions)
         is_expected.to be_allowed(:award_emoji)
         is_expected.to be_allowed(*author_permissions)
       end

spec/policies/project_snippet_policy_spec.rb

@@ -41,7 +41,7 @@ describe ProjectSnippetPolicy do
       subject { abilities(regular_user, :public) }
 
       it do
-        expect_allowed(:read_project_snippet)
+        expect_allowed(:read_project_snippet, :create_note)
         expect_disallowed(*author_permissions)
       end
     end
@@ -50,7 +50,7 @@ describe ProjectSnippetPolicy do
       subject { abilities(external_user, :public) }
 
       it do
-        expect_allowed(:read_project_snippet)
+        expect_allowed(:read_project_snippet, :create_note)
         expect_disallowed(*author_permissions)
       end
     end
@@ -70,7 +70,7 @@ describe ProjectSnippetPolicy do
       subject { abilities(regular_user, :internal) }
 
       it do
-        expect_allowed(:read_project_snippet)
+        expect_allowed(:read_project_snippet, :create_note)
         expect_disallowed(*author_permissions)
       end
     end
@@ -79,7 +79,7 @@ describe ProjectSnippetPolicy do
       subject { abilities(external_user, :internal) }
 
       it do
-        expect_disallowed(:read_project_snippet)
+        expect_disallowed(:read_project_snippet, :create_note)
         expect_disallowed(*author_permissions)
       end
     end
@@ -92,7 +92,7 @@ describe ProjectSnippetPolicy do
       end
 
       it do
-        expect_allowed(:read_project_snippet)
+        expect_allowed(:read_project_snippet, :create_note)
         expect_disallowed(*author_permissions)
       end
     end
@@ -112,7 +112,7 @@ describe ProjectSnippetPolicy do
       subject { abilities(regular_user, :private) }
 
       it do
-        expect_disallowed(:read_project_snippet)
+        expect_disallowed(:read_project_snippet, :create_note)
         expect_disallowed(*author_permissions)
       end
     end
@@ -123,7 +123,7 @@ describe ProjectSnippetPolicy do
       subject { described_class.new(regular_user, snippet) }
 
       it do
-        expect_allowed(:read_project_snippet)
+        expect_allowed(:read_project_snippet, :create_note)
         expect_allowed(*author_permissions)
       end
     end
@@ -136,7 +136,7 @@ describe ProjectSnippetPolicy do
       end
 
       it do
-        expect_allowed(:read_project_snippet)
+        expect_allowed(:read_project_snippet, :create_note)
         expect_disallowed(*author_permissions)
       end
     end
@@ -149,7 +149,7 @@ describe ProjectSnippetPolicy do
       end
 
       it do
-        expect_allowed(:read_project_snippet)
+        expect_allowed(:read_project_snippet, :create_note)
         expect_disallowed(*author_permissions)
       end
     end
@@ -158,7 +158,7 @@ describe ProjectSnippetPolicy do
       subject { abilities(create(:admin), :private) }
 
       it do
-        expect_allowed(:read_project_snippet)
+        expect_allowed(:read_project_snippet, :create_note)
         expect_allowed(*author_permissions)
       end
     end

spec/services/notes/build_service_spec.rb

@@ -45,6 +45,15 @@ describe Notes::BuildService do
         end
       end
 
+      context 'when user has no access to discussion' do
+        it 'sets an error' do
+          another_user = create(:user)
+          new_note = described_class.new(project, another_user, note: 'Test', in_reply_to_discussion_id: note.discussion_id).execute
+
+          expect(new_note.errors[:base]).to include('Discussion to reply to cannot be found')
+        end
+      end
+
       context 'personal snippet note' do
         def reply(note, user = nil)
           user ||= create(:user)

spec/services/notes/create_service_spec.rb

@@ -127,6 +127,10 @@ describe Notes::CreateService do
         create(:diff_note_on_merge_request, noteable: merge_request, project: project_with_repo)
       end
 
+      before do
+        project_with_repo.add_maintainer(user)
+      end
+
       context 'when eligible to have a note diff file' do
         let(:new_opts) do
           opts.merge(in_reply_to_discussion_id: nil,