Send TODOs for comments on commits correctly

At present, the TodoService uses the `:read_project` ability to decide
whether a user can read a note on a commit. However, commits can have a
visibility level that is more restricted than the project, so this is a
security issue.

This commit changes the code to use the `:read_commit` ability in this
case instead, which ensures TODOs are only generated for commit notes
if the users can see the commit.

3 files changed, 112 insertions, 20 deletions

diff --git a/app/services/todo_service.rb b/app/services/todo_service.rb
index 0ea230a44a1..b1256df35d6 100644
--- a/app/services/todo_service.rb
+++ b/app/services/todo_service.rb
@@ -314,11 +314,9 @@ class TodoService
   end
 
   def reject_users_without_access(users, parent, target)
-    if target.is_a?(Note) && target.for_issuable?
-      target = target.noteable
-    end
+    target = target.noteable if target.is_a?(Note)
 
-    if target.is_a?(Issuable)
+    if target.respond_to?(:to_ability_name)
       select_users(users, :"read_#{target.to_ability_name}", target)
     else
       select_users(users, :read_project, parent)
diff --git a/changelogs/unreleased/security-64711-fix-commit-todos.yml b/changelogs/unreleased/security-64711-fix-commit-todos.yml
new file mode 100644
index 00000000000..ce4b3cdeeaf
--- /dev/null
+++ b/changelogs/unreleased/security-64711-fix-commit-todos.yml
@@ -0,0 +1,5 @@
+---
+title: Send TODOs for comments on commits correctly
+merge_request:
+author:
+type: security
diff --git a/spec/services/todo_service_spec.rb b/spec/services/todo_service_spec.rb
index 9ee23f3eb48..bdf2f59704c 100644
--- a/spec/services/todo_service_spec.rb
+++ b/spec/services/todo_service_spec.rb
@@ -436,25 +436,114 @@ describe TodoService do
         should_create_todo(user: john_doe, target: confidential_issue, author: john_doe, action: Todo::DIRECTLY_ADDRESSED, note: addressed_note_on_confidential_issue)
       end
 
-      context 'on commit' do
-        let(:project) { create(:project, :repository) }
-
-        it 'creates a todo for each valid mentioned user when leaving a note on commit' do
-          service.new_note(note_on_commit, john_doe)
-
-          should_create_todo(user: member, target_id: nil, target_type: 'Commit', commit_id: note_on_commit.commit_id, author: john_doe, action: Todo::MENTIONED, note: note_on_commit)
-          should_create_todo(user: author, target_id: nil, target_type: 'Commit', commit_id: note_on_commit.commit_id, author: john_doe, action: Todo::MENTIONED, note: note_on_commit)
-          should_create_todo(user: john_doe, target_id: nil, target_type: 'Commit', commit_id: note_on_commit.commit_id, author: john_doe, action: Todo::MENTIONED, note: note_on_commit)
-          should_not_create_todo(user: non_member, target_id: nil, target_type: 'Commit', commit_id: note_on_commit.commit_id, author: john_doe, action: Todo::MENTIONED, note: note_on_commit)
+      context 'commits' do
+        let(:base_commit_todo_attrs) { { target_id: nil, target_type: 'Commit', author: john_doe } }
+
+        context 'leaving a note on a commit in a public project' do
+          let(:project) { create(:project, :repository, :public) }
+          it 'creates a todo for each valid mentioned user' do
+            expected_todo = base_commit_todo_attrs.merge(
+              action: Todo::MENTIONED,
+              note: note_on_commit,
+              commit_id: note_on_commit.commit_id
+            )
+
+            service.new_note(note_on_commit, john_doe)
+
+            should_create_todo(expected_todo.merge(user: member))
+            should_create_todo(expected_todo.merge(user: author))
+            should_create_todo(expected_todo.merge(user: john_doe))
+            should_create_todo(expected_todo.merge(user: guest))
+            should_create_todo(expected_todo.merge(user: non_member))
+          end
+
+          it 'creates a directly addressed todo for each valid mentioned user' do
+            expected_todo = base_commit_todo_attrs.merge(
+              action: Todo::DIRECTLY_ADDRESSED,
+              note: addressed_note_on_commit,
+              commit_id: addressed_note_on_commit.commit_id
+            )
+
+            service.new_note(addressed_note_on_commit, john_doe)
+
+            should_create_todo(expected_todo.merge(user: member))
+            should_create_todo(expected_todo.merge(user: author))
+            should_create_todo(expected_todo.merge(user: john_doe))
+            should_create_todo(expected_todo.merge(user: guest))
+            should_create_todo(expected_todo.merge(user: non_member))
+          end
         end
 
-        it 'creates a directly addressed todo for each valid mentioned user when leaving a note on commit' do
-          service.new_note(addressed_note_on_commit, john_doe)
+        context 'leaving a note on a commit in a public project with private code' do
+          let(:project) { create(:project, :repository, :public, :repository_private) }
+
+          it 'creates a todo for each valid mentioned user' do
+            expected_todo = base_commit_todo_attrs.merge(
+              action: Todo::MENTIONED,
+              note: note_on_commit,
+              commit_id: note_on_commit.commit_id
+            )
+
+            service.new_note(note_on_commit, john_doe)
+
+            should_create_todo(expected_todo.merge(user: member))
+            should_create_todo(expected_todo.merge(user: author))
+            should_create_todo(expected_todo.merge(user: john_doe))
+            should_create_todo(expected_todo.merge(user: guest))
+            should_not_create_todo(expected_todo.merge(user: non_member))
+          end
+
+          it 'creates a directly addressed todo for each valid mentioned user' do
+            expected_todo = base_commit_todo_attrs.merge(
+              action: Todo::DIRECTLY_ADDRESSED,
+              note: addressed_note_on_commit,
+              commit_id: addressed_note_on_commit.commit_id
+            )
+
+            service.new_note(addressed_note_on_commit, john_doe)
+
+            should_create_todo(expected_todo.merge(user: member))
+            should_create_todo(expected_todo.merge(user: author))
+            should_create_todo(expected_todo.merge(user: john_doe))
+            should_create_todo(expected_todo.merge(user: guest))
+            should_not_create_todo(expected_todo.merge(user: non_member))
+          end
+        end
 
-          should_create_todo(user: member, target_id: nil, target_type: 'Commit', commit_id: addressed_note_on_commit.commit_id, author: john_doe, action: Todo::DIRECTLY_ADDRESSED, note: addressed_note_on_commit)
-          should_create_todo(user: author, target_id: nil, target_type: 'Commit', commit_id: addressed_note_on_commit.commit_id, author: john_doe, action: Todo::DIRECTLY_ADDRESSED, note: addressed_note_on_commit)
-          should_create_todo(user: john_doe, target_id: nil, target_type: 'Commit', commit_id: addressed_note_on_commit.commit_id, author: john_doe, action: Todo::DIRECTLY_ADDRESSED, note: addressed_note_on_commit)
-          should_not_create_todo(user: non_member, target_id: nil, target_type: 'Commit', commit_id: addressed_note_on_commit.commit_id, author: john_doe, action: Todo::DIRECTLY_ADDRESSED, note: addressed_note_on_commit)
+        context 'leaving a note on a commit in a private project' do
+          let(:project) { create(:project, :repository, :private) }
+
+          it 'creates a todo for each valid mentioned user' do
+            expected_todo = base_commit_todo_attrs.merge(
+              action: Todo::MENTIONED,
+              note: note_on_commit,
+              commit_id: note_on_commit.commit_id
+            )
+
+            service.new_note(note_on_commit, john_doe)
+
+            should_create_todo(expected_todo.merge(user: member))
+            should_create_todo(expected_todo.merge(user: author))
+            should_create_todo(expected_todo.merge(user: john_doe))
+            should_not_create_todo(expected_todo.merge(user: guest))
+            should_not_create_todo(expected_todo.merge(user: non_member))
+          end
+
+          it 'creates a directly addressed todo for each valid mentioned user' do
+            expected_todo = base_commit_todo_attrs.merge(
+              action: Todo::DIRECTLY_ADDRESSED,
+              note: addressed_note_on_commit,
+              commit_id: addressed_note_on_commit.commit_id
+            )
+
+            service.new_note(addressed_note_on_commit, john_doe)
+
+            should_create_todo(expected_todo.merge(user: member))
+            should_create_todo(expected_todo.merge(user: author))
+            should_create_todo(expected_todo.merge(user: john_doe))
+            should_not_create_todo(expected_todo.merge(user: guest))
+            should_not_create_todo(expected_todo.merge(user: non_member))
+          end
         end
       end