Add the ability to set the CSP nonce only to the specified directives

I changed to set CSP nonce to `style-src` directive in #32932.
But this causes an issue when `unsafe-inline` is specified to `style-src`
(If a nonce is present, a nonce takes precedence over `unsafe-inline`).

So, I fixed to nonce directives configurable. By configure this, users
can make CSP as before.

Fixes #35137.

actionpack/CHANGELOG.md

@@ -1,3 +1,9 @@
+*   Add the ability to set the CSP nonce only to the specified directives.
+
+    Fixes #35137.
+
+    *Yuji Yaginuma*
+
 *   Keep part when scope option has value.
 
     When a route was defined within an optional scope, if that route didn't

actionpack/lib/action_dispatch/http/content_security_policy.rb

@@ -22,8 +22,9 @@ module ActionDispatch #:nodoc:
 
         if policy = request.content_security_policy
           nonce = request.content_security_policy_nonce
+          nonce_directives = request.content_security_policy_nonce_directives
           context = request.controller_instance || request
-          headers[header_name(request)] = policy.build(context, nonce)
+          headers[header_name(request)] = policy.build(context, nonce, nonce_directives)
         end
 
         response
@@ -54,6 +55,7 @@ module ActionDispatch #:nodoc:
       POLICY_REPORT_ONLY = "action_dispatch.content_security_policy_report_only"
       NONCE_GENERATOR = "action_dispatch.content_security_policy_nonce_generator"
       NONCE = "action_dispatch.content_security_policy_nonce"
+      NONCE_DIRECTIVES = "action_dispatch.content_security_policy_nonce_directives"
 
       def content_security_policy
         get_header(POLICY)
@@ -79,6 +81,14 @@ module ActionDispatch #:nodoc:
         set_header(NONCE_GENERATOR, generator)
       end
 
+      def content_security_policy_nonce_directives
+        get_header(NONCE_DIRECTIVES)
+      end
+
+      def content_security_policy_nonce_directives=(generator)
+        set_header(NONCE_DIRECTIVES, generator)
+      end
+
       def content_security_policy_nonce
         if content_security_policy_nonce_generator
           if nonce = get_header(NONCE)
@@ -131,9 +141,9 @@ module ActionDispatch #:nodoc:
       worker_src:      "worker-src"
     }.freeze
 
-    NONCE_DIRECTIVES = %w[script-src style-src].freeze
+    DEFAULT_NONCE_DIRECTIVES = %w[script-src style-src].freeze
 
-    private_constant :MAPPINGS, :DIRECTIVES, :NONCE_DIRECTIVES
+    private_constant :MAPPINGS, :DIRECTIVES, :DEFAULT_NONCE_DIRECTIVES
 
     attr_reader :directives
 
@@ -202,8 +212,9 @@ module ActionDispatch #:nodoc:
       end
     end
 
-    def build(context = nil, nonce = nil)
-      build_directives(context, nonce).compact.join("; ")
+    def build(context = nil, nonce = nil, nonce_directives = nil)
+      nonce_directives = DEFAULT_NONCE_DIRECTIVES if nonce_directives.nil?
+      build_directives(context, nonce, nonce_directives).compact.join("; ")
     end
 
     private
@@ -226,10 +237,10 @@ module ActionDispatch #:nodoc:
         end
       end
 
-      def build_directives(context, nonce)
+      def build_directives(context, nonce, nonce_directives)
         @directives.map do |directive, sources|
           if sources.is_a?(Array)
-            if nonce && nonce_directive?(directive)
+            if nonce && nonce_directive?(directive, nonce_directives)
               "#{directive} #{build_directive(sources, context).join(' ')} 'nonce-#{nonce}'"
             else
               "#{directive} #{build_directive(sources, context).join(' ')}"
@@ -264,8 +275,8 @@ module ActionDispatch #:nodoc:
         end
       end
 
-      def nonce_directive?(directive)
-        NONCE_DIRECTIVES.include?(directive)
+      def nonce_directive?(directive, nonce_directives)
+        nonce_directives.include?(directive)
       end
   end
 end

actionpack/test/dispatch/content_security_policy_test.rb

@@ -542,3 +542,57 @@ class DisabledContentSecurityPolicyIntegrationTest < ActionDispatch::Integration
     assert_equal "default-src https://example.com", response.headers["Content-Security-Policy"]
   end
 end
+
+class NonceDirectiveContentSecurityPolicyIntegrationTest < ActionDispatch::IntegrationTest
+  class PolicyController < ActionController::Base
+    def index
+      head :ok
+    end
+  end
+
+  ROUTES = ActionDispatch::Routing::RouteSet.new
+  ROUTES.draw do
+    scope module: "nonce_directive_content_security_policy_integration_test" do
+      get "/", to: "policy#index"
+    end
+  end
+
+  POLICY = ActionDispatch::ContentSecurityPolicy.new do |p|
+    p.default_src -> { :self  }
+    p.script_src -> { :https }
+    p.style_src -> { :https }
+  end
+
+  class PolicyConfigMiddleware
+    def initialize(app)
+      @app = app
+    end
+
+    def call(env)
+      env["action_dispatch.content_security_policy"] = POLICY
+      env["action_dispatch.content_security_policy_nonce_generator"] = proc { "iyhD0Yc0W+c=" }
+      env["action_dispatch.content_security_policy_report_only"] = false
+      env["action_dispatch.content_security_policy_nonce_directives"] = %w(script-src)
+      env["action_dispatch.show_exceptions"] = false
+
+      @app.call(env)
+    end
+  end
+
+  APP = build_app(ROUTES) do |middleware|
+    middleware.use PolicyConfigMiddleware
+    middleware.use ActionDispatch::ContentSecurityPolicy::Middleware
+  end
+
+  def app
+    APP
+  end
+
+  def test_generate_nonce_only_specified_in_nonce_directives
+    get "/"
+
+    assert_response :success
+    assert_match "script-src https: 'nonce-iyhD0Yc0W+c='", response.headers["Content-Security-Policy"]
+    assert_no_match "style-src https: 'nonce-iyhD0Yc0W+c='", response.headers["Content-Security-Policy"]
+  end
+end

railties/lib/rails/application.rb

@@ -270,7 +270,8 @@ module Rails
           "action_dispatch.use_cookies_with_metadata" => config.action_dispatch.use_cookies_with_metadata,
           "action_dispatch.content_security_policy" => config.content_security_policy,
           "action_dispatch.content_security_policy_report_only" => config.content_security_policy_report_only,
-          "action_dispatch.content_security_policy_nonce_generator" => config.content_security_policy_nonce_generator
+          "action_dispatch.content_security_policy_nonce_generator" => config.content_security_policy_nonce_generator,
+          "action_dispatch.content_security_policy_nonce_directives" => config.content_security_policy_nonce_directives
         )
       end
     end

railties/lib/rails/application/configuration.rb

@@ -18,8 +18,8 @@ module Rails
                     :session_options, :time_zone, :reload_classes_only_on_change,
                     :beginning_of_week, :filter_redirect, :x, :enable_dependency_loading,
                     :read_encrypted_secrets, :log_level, :content_security_policy_report_only,
-                    :content_security_policy_nonce_generator, :require_master_key, :credentials,
-                    :disable_sandbox, :add_autoload_paths_to_load_path
+                    :content_security_policy_nonce_generator, :content_security_policy_nonce_directives,
+                    :require_master_key, :credentials, :disable_sandbox, :add_autoload_paths_to_load_path
 
       attr_reader :encoding, :api_only, :loaded_config_version, :autoloader
 
@@ -60,6 +60,7 @@ module Rails
         @content_security_policy                 = nil
         @content_security_policy_report_only     = false
         @content_security_policy_nonce_generator = nil
+        @content_security_policy_nonce_directives = nil
         @require_master_key                      = false
         @loaded_config_version                   = nil
         @credentials                             = ActiveSupport::OrderedOptions.new

railties/lib/rails/generators/rails/app/templates/config/initializers/content_security_policy.rb.tt

@@ -23,6 +23,9 @@
 # If you are using UJS then enable automatic nonce generation
 # Rails.application.config.content_security_policy_nonce_generator = -> request { SecureRandom.base64(16) }
 
+# Set the nonce only to specific directives
+# Rails.application.config.content_security_policy_nonce_directives = %w(script-src)
+
 # Report CSP violations to a specified URI
 # For further information see the following documentation:
 # https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy-Report-Only

railties/test/application/content_security_policy_test.rb

@@ -119,6 +119,38 @@ module ApplicationTests
       assert_policy "default-src 'self' https:", report_only: true
     end
 
+    test "global content security policy nonce directives in an initializer" do
+      controller :pages, <<-RUBY
+        class PagesController < ApplicationController
+          def index
+            render html: "<h1>Welcome to Rails!</h1>"
+          end
+        end
+      RUBY
+
+      app_file "config/initializers/content_security_policy.rb", <<-RUBY
+        Rails.application.config.content_security_policy do |p|
+          p.default_src :self, :https
+          p.script_src  :self, :https
+          p.style_src   :self, :https
+        end
+
+        Rails.application.config.content_security_policy_nonce_generator = proc { "iyhD0Yc0W+c=" }
+        Rails.application.config.content_security_policy_nonce_directives = %w(script-src)
+      RUBY
+
+      app_file "config/routes.rb", <<-RUBY
+        Rails.application.routes.draw do
+          root to: "pages#index"
+        end
+      RUBY
+
+      app("development")
+
+      get "/"
+      assert_policy "default-src 'self' https:; script-src 'self' https: 'nonce-iyhD0Yc0W+c='; style-src 'self' https:"
+    end
+
     test "override content security policy in a controller" do
       controller :pages, <<-RUBY
         class PagesController < ApplicationController