Add support for Content-Security-Policy

A nonce-based Content-Security-Policy thwarts XSS attacks by allowing
inline JavaScript to execute if the script nonce matches the header
value. Rails 5.2 supports nonce-based Content-Security-Policy headers,
so provide configuration to enable this and make it work.

To support this, we need to change all `:javascript` HAML filters to the
following form:

```
= javascript_tag nonce: true do
  :plain
    ...
```

We use `%script` throughout our HAML to store JSON and other text, but
since this doesn't execute, browsers don't appear to block this content
from being used and require the nonce value to be present.

1 files changed, 59 insertions, 0 deletions

diff --git a/spec/lib/gitlab/content_security_policy/config_loader_spec.rb b/spec/lib/gitlab/content_security_policy/config_loader_spec.rb
new file mode 100644
index 00000000000..e7670c9d523
--- /dev/null
+++ b/spec/lib/gitlab/content_security_policy/config_loader_spec.rb
@@ -0,0 +1,59 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::ContentSecurityPolicy::ConfigLoader do
+  let(:policy) { ActionDispatch::ContentSecurityPolicy.new }
+  let(:csp_config) do
+    {
+      enabled: true,
+      report_only: false,
+      directives: {
+        base_uri: 'http://example.com',
+        child_src: "'self' https://child.example.com",
+        default_src: "'self' https://other.example.com",
+        script_src: "'self'  https://script.exammple.com ",
+        worker_src: "data:  https://worker.example.com"
+      }
+    }
+  end
+
+  context '.default_settings_hash' do
+    it 'returns empty defaults' do
+      settings = described_class.default_settings_hash
+
+      expect(settings['enabled']).to be_falsey
+      expect(settings['report_only']).to be_falsey
+
+      described_class::DIRECTIVES.each do |directive|
+        expect(settings['directives'].has_key?(directive)).to be_truthy
+        expect(settings['directives'][directive]).to be_nil
+      end
+    end
+  end
+
+  context '#load' do
+    subject { described_class.new(csp_config[:directives]) }
+
+    def expected_config(directive)
+      csp_config[:directives][directive].split(' ').map(&:strip)
+    end
+
+    it 'sets the policy properly' do
+      subject.load(policy)
+
+      expect(policy.directives['base-uri']).to eq([csp_config[:directives][:base_uri]])
+      expect(policy.directives['default-src']).to eq(expected_config(:default_src))
+      expect(policy.directives['child-src']).to eq(expected_config(:child_src))
+      expect(policy.directives['worker-src']).to eq(expected_config(:worker_src))
+    end
+
+    it 'ignores malformed policy statements' do
+      csp_config[:directives][:base_uri] = 123
+
+      subject.load(policy)
+
+      expect(policy.directives['base-uri']).to be_nil
+    end
+  end
+end