Remove persistent XSS vulnerability in `commit_person_link` helper

Because we were incorrectly supplying the tooltip title as
`data-original-title` (which Bootstrap's Tooltip JS automatically
applies based on the `title` attribute; we should never be setting it
directly), the value was being passed through as-is.

Instead, we should be supplying the normal `title` attribute and letting
Rails escape the value, which also negates the need for us to call
`sanitize` on it.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/15126

app/helpers/commits_helper.rb

@@ -183,7 +183,7 @@ module CommitsHelper
 
     options = {
       class: "commit-#{options[:source]}-link has-tooltip",
-      data: { 'original-title'.to_sym => sanitize(source_email) }
+      title: source_email
     }
 
     if user.nil?

features/steps/project/commits/user_lookup.rb

@@ -29,8 +29,9 @@ class Spinach::Features::ProjectCommitsUserLookup < Spinach::FeatureSteps
 
   def check_author_link(email, user)
     author_link = find('.commit-author-link')
+
     expect(author_link['href']).to eq user_path(user)
-    expect(author_link['data-original-title']).to eq email
+    expect(author_link['title']).to eq email
     expect(find('.commit-author-name').text).to eq user.name
   end
 

spec/helpers/commits_helper_spec.rb

@@ -0,0 +1,29 @@
+require 'rails_helper'
+
+describe CommitsHelper do
+  describe 'commit_author_link' do
+    it 'escapes the author email' do
+      commit = double(
+        author: nil,
+        author_name: 'Persistent XSS',
+        author_email: 'my@email.com" onmouseover="alert(1)'
+      )
+
+      expect(helper.commit_author_link(commit)).
+        not_to include('onmouseover="alert(1)"')
+    end
+  end
+
+  describe 'commit_committer_link' do
+    it 'escapes the committer email' do
+      commit = double(
+        committer: nil,
+        committer_name: 'Persistent XSS',
+        committer_email: 'my@email.com" onmouseover="alert(1)'
+      )
+
+      expect(helper.commit_committer_link(commit)).
+        not_to include('onmouseover="alert(1)"')
+    end
+  end
+end