Disable caching on API project/raw endpoint

Caching of file contents creates an inconsistency in the value of the
Content-Disposition header, allowing files that should only be sent as
"attachment" to instead be returned as "inline," causing them to be
evaluated and executed by the receiving client. This is due to how
gitaly and the main Rails application coordinate around evaluating etags
for content freshness. This fix addresses the issue by removing caching
from this endpoint, but does not address the underlying issue (namely
that Rails can not accurately determine the file type of the requested
content, thus can not be responsible for determining appropriate or safe
Content-Disposition.)

app/controllers/application_controller.rb

@@ -5,6 +5,7 @@ require 'fogbugz'
 
 class ApplicationController < ActionController::Base
   include Gitlab::GonHelper
+  include Gitlab::NoCacheHeaders
   include GitlabRoutingHelper
   include PageLayoutHelper
   include SafeParamsHelper
@@ -55,7 +56,6 @@ class ApplicationController < ActionController::Base
   # Adds `no-store` to the DEFAULT_CACHE_CONTROL, to prevent security
   # concerns due to caching private data.
   DEFAULT_GITLAB_CACHE_CONTROL = "#{ActionDispatch::Http::Cache::Response::DEFAULT_CACHE_CONTROL}, no-store"
-  DEFAULT_GITLAB_CONTROL_NO_CACHE = "#{DEFAULT_GITLAB_CACHE_CONTROL}, no-cache"
 
   rescue_from Encoding::CompatibilityError do |exception|
     log_exception(exception)
@@ -247,9 +247,9 @@ class ApplicationController < ActionController::Base
   end
 
   def no_cache_headers
-    headers['Cache-Control'] = DEFAULT_GITLAB_CONTROL_NO_CACHE
-    headers['Pragma'] = 'no-cache' # HTTP 1.0 compatibility
-    headers['Expires'] = 'Fri, 01 Jan 1990 00:00:00 GMT'
+    DEFAULT_GITLAB_NO_CACHE_HEADERS.each do |k, v|
+      headers[k] = v
+    end
   end
 
   def default_headers

changelogs/unreleased/security-remove-caching-from-api-project-raw-endpoint.yml

+---
+title: Disable caching of repository/files/:file_path/raw API endpoint
+merge_request:
+author:
+type: security

lib/api/files.rb

@@ -127,6 +127,7 @@ module API
       get ":id/repository/files/:file_path/raw", requirements: FILE_ENDPOINT_REQUIREMENTS do
         assign_file_vars!
 
+        no_cache_headers
         set_http_headers(blob_data)
 
         send_git_blob @repo, @blob

lib/api/helpers/headers_helpers.rb

@@ -3,6 +3,8 @@
 module API
   module Helpers
     module HeadersHelpers
+      include Gitlab::NoCacheHeaders
+
       def set_http_headers(header_data)
         header_data.each do |key, value|
           if value.is_a?(Enumerable)
@@ -12,6 +14,12 @@ module API
           header "X-Gitlab-#{key.to_s.split('_').collect(&:capitalize).join('-')}", value.to_s
         end
       end
+
+      def no_cache_headers
+        DEFAULT_GITLAB_NO_CACHE_HEADERS.each do |k, v|
+          header k, v
+        end
+      end
     end
   end
 end

lib/gitlab/no_cache_headers.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module NoCacheHeaders
+    DEFAULT_GITLAB_NO_CACHE_HEADERS = {
+      'Cache-Control' => "#{ActionDispatch::Http::Cache::Response::DEFAULT_CACHE_CONTROL}, no-store, no-cache",
+      'Pragma'        => 'no-cache', # HTTP 1.0 compatibility
+      'Expires'       => 'Fri, 01 Jan 1990 00:00:00 GMT'
+    }.freeze
+
+    def no_cache_headers
+      raise "#no_cache_headers is not implemented for this object"
+    end
+  end
+end

qa/qa/specs/features/api/3_create/repository/files_spec.rb

@@ -59,5 +59,48 @@ module QA
         a_hash_including(message: '202 Accepted')
       )
     end
+
+    describe 'raw file access' do
+      let(:svg_file) do
+        <<-SVG
+          <?xml version="1.0" standalone="no"?>
+          <!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
+
+          <svg version="1.1" baseProfile="full" xmlns="http://www.w3.org/2000/svg">
+            <polygon id="triangle" points="0,0 0,50 50,0" fill="#009900" stroke="#004400"/>
+            <script type="text/javascript">
+               alert("surprise");
+            </script>
+          </svg>
+        SVG
+      end
+
+      it 'sets no-cache headers as expected' do
+        create_project_request = Runtime::API::Request.new(@api_client, '/projects')
+        post create_project_request.url, path: project_name, name: project_name
+
+        create_file_request = Runtime::API::Request.new(@api_client, "/projects/#{sanitized_project_path}/repository/files/test.svg")
+        post create_file_request.url, branch: 'master', content: svg_file, commit_message: 'Add test.svg'
+
+        get_file_request = Runtime::API::Request.new(@api_client, "/projects/#{sanitized_project_path}/repository/files/test.svg/raw", ref: 'master')
+
+        3.times do
+          response = get get_file_request.url
+
+          # Subsequent responses aren't cached, so headers should match from
+          #   request to request, especially a 200 response rather than a 304
+          #   (indicating a cached response.) Further, :content_disposition
+          #   should include `attachment` for all responses.
+          #
+          expect(response.headers[:cache_control]).to include("no-store")
+          expect(response.headers[:cache_control]).to include("no-cache")
+          expect(response.headers[:pragma]).to eq("no-cache")
+          expect(response.headers[:expires]).to eq("Fri, 01 Jan 1990 00:00:00 GMT")
+          expect(response.headers[:content_disposition]).to include("attachment")
+          expect(response.headers[:content_disposition]).not_to include("inline")
+          expect(response.headers[:content_type]).to include("image/svg+xml")
+        end
+      end
+    end
   end
 end

spec/lib/gitlab/no_cache_headers_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::NoCacheHeaders do
+  class NoCacheTester
+    include Gitlab::NoCacheHeaders
+  end
+
+  describe "#no_cache_headers" do
+    subject { NoCacheTester.new }
+
+    it "raises a RuntimeError" do
+      expect { subject.no_cache_headers }.to raise_error(RuntimeError)
+    end
+  end
+end

spec/requests/api/files_spec.rb

@@ -447,6 +447,18 @@ describe API::Files do
         expect(response).to have_gitlab_http_status(200)
       end
 
+      it 'sets no-cache headers' do
+        url = route('.gitignore') + "/raw"
+        expect(Gitlab::Workhorse).to receive(:send_git_blob)
+
+        get api(url, current_user), params: params
+
+        expect(response.headers["Cache-Control"]).to include("no-store")
+        expect(response.headers["Cache-Control"]).to include("no-cache")
+        expect(response.headers["Pragma"]).to eq("no-cache")
+        expect(response.headers["Expires"]).to eq("Fri, 01 Jan 1990 00:00:00 GMT")
+      end
+
       context 'when mandatory params are not given' do
         it_behaves_like '400 response' do
           let(:request) { get api(route("any%2Ffile"), current_user) }