fix(swagger): prevent path traversal in docs controller (#14458)

This hardens the development/test Swagger docs endpoint by ensuring
requested files are resolved only within the `swagger/` directory.

This did not affect production security because the Swagger controller
only renders files in development or test environments; production
already returns `404`. The change still closes the scanner finding and
prevents future automated reports from flagging the development-only
path.

## Closes

Addresses: GHSA-xhp7-ggjq-p2rg

## How to reproduce

1. Start Chatwoot locally in development.
2. Visit `/swagger/%2Fetc%2Fpasswd`.
3. Before this change, the endpoint could render files outside the
Swagger directory in development/test.

## What changed

- Resolve Swagger file requests relative to `Rails.root/swagger`.
- Return `404` when the resolved path is outside the Swagger directory
or does not point to a file.
- Strip leading slashes from derived request paths.
- Add a request spec for the encoded absolute-path case.

## How to test

1. Start the app locally.
2. Visit `/swagger` and confirm the ReDoc page loads.
3. Visit `/swagger/swagger.json` and confirm the Swagger JSON loads.
4. Visit `/swagger/%2Fetc%2Fpasswd` and confirm it returns `404` with no
file contents.

Note: `bundle exec rspec spec/controllers/swagger_controller_spec.rb`
was passing locally earlier during this fix. A final rerun before
opening the PR was blocked because local Postgres on `localhost:5432`
was not accepting connections.

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

app/controllers/swagger_controller.rb

@@ -1,7 +1,12 @@
 class SwaggerController < ApplicationController
   def respond
     if Rails.env.development? || Rails.env.test?
-      render inline: Rails.root.join('swagger', derived_path).read
+      swagger_root = Rails.root.join('swagger')
+      file_path = swagger_root.join(derived_path).cleanpath
+
+      return head :not_found unless file_path.to_s.start_with?("#{swagger_root}/") && file_path.file?
+
+      render inline: file_path.read
     else
       head :not_found
     end
@@ -11,8 +16,8 @@ class SwaggerController < ApplicationController
 
   def derived_path
     params[:path] ||= 'index.html'
-    path = Rack::Utils.clean_path_info(params[:path])
-    path << ".#{Rack::Utils.clean_path_info(params[:format])}" unless path.ends_with?(params[:format].to_s)
+    path = Rack::Utils.clean_path_info(params[:path]).delete_prefix('/')
+    path << ".#{Rack::Utils.clean_path_info(params[:format]).delete_prefix('/')}" unless path.ends_with?(params[:format].to_s)
     path
   end
 end

spec/controllers/swagger_controller_spec.rb

@@ -8,5 +8,10 @@ describe '/swagger', type: :request do
       expect(response.body).to include('redoc')
       expect(response.body).to include('/swagger.json')
     end
+
+    it 'does not render files outside the swagger directory' do
+      get '/swagger/%2Fetc%2Fpasswd'
+      expect(response).to have_http_status(:not_found)
+    end
   end
 end