Ignore invalid trusted proxies in X-Forwarded-For header

Certain reverse proxies can send invalid IP addresses in the X-Forwarded-For header
For example, Apache can send (null).

Closes #20194

CHANGELOG

@@ -8,6 +8,7 @@ v 8.11.0 (unreleased)
   - Add GitLab Workhorse version to admin dashboard (Katarzyna Kobierska Ula Budziszewska)
 
 v 8.10.1 (unreleased)
+  - Ignore invalid trusted proxies in X-Forwarded-For header
   - Fix bug where replies to commit notes displayed in the MR discussion tab wouldn't show up on the commit page
 
 v 8.10.0

config/initializers/trusted_proxies.rb

@@ -11,6 +11,12 @@ module Rack
   end
 end
 
+gitlab_trusted_proxies = Array(Gitlab.config.gitlab.trusted_proxies).map do |proxy|
+  begin
+    IPAddr.new(proxy)
+  rescue IPAddr::InvalidAddressError
+  end
+end.compact
+
 Rails.application.config.action_dispatch.trusted_proxies = (
-  [ '127.0.0.1', '::1' ] + Array(Gitlab.config.gitlab.trusted_proxies)
-).map { |proxy| IPAddr.new(proxy) }
+  [ '127.0.0.1', '::1' ] + gitlab_trusted_proxies)

spec/initializers/trusted_proxies_spec.rb

@@ -17,6 +17,12 @@ describe 'trusted_proxies', lib: true do
       expect(request.remote_ip).to eq('10.1.5.89')
       expect(request.ip).to eq('10.1.5.89')
     end
+
+    it 'filters out bad values' do
+      request = stub_request('HTTP_X_FORWARDED_FOR' => '(null), 10.1.5.89')
+      expect(request.remote_ip).to eq('10.1.5.89')
+      expect(request.ip).to eq('10.1.5.89')
+    end
   end
 
   context 'with private IP ranges added' do