Override hostname when connecting via Kubeclient

Kubeclient uses rest-client. We hack into to access the net/http object
so that we can patch to connect to the resolved IP + set
hostname_override.

Add specs for discord. The discord integration also uses rest-client, so
since we patched rest-client, spec that the DNS rebinding protection
works

1 files changed, 49 insertions, 0 deletions

diff --git a/config/initializers/rest-client-hostname_override.rb b/config/initializers/rest-client-hostname_override.rb
new file mode 100644
index 00000000000..bc1b70bd73f
--- /dev/null
+++ b/config/initializers/rest-client-hostname_override.rb
@@ -0,0 +1,49 @@
+# frozen_string_literal: true
+
+module RestClient
+  class Request
+    attr_accessor :hostname_override
+
+    module UrlBlocker
+      def transmit(uri, req, payload, &block)
+        begin
+          ip, hostname_override = Gitlab::UrlBlocker.validate!(uri, allow_local_network: allow_settings_local_requests?,
+                                                               allow_localhost: allow_settings_local_requests?,
+                                                               dns_rebind_protection: dns_rebind_protection?)
+
+          self.hostname_override = hostname_override
+        rescue Gitlab::UrlBlocker::BlockedUrlError => e
+          raise ArgumentError, "URL '#{uri}' is blocked: #{e.message}"
+        end
+
+        # Gitlab::UrlBlocker returns a Addressable::URI which we need to coerce
+        # to URI so that rest-client can use it to determine if it's a
+        # URI::HTTPS or not. It uses it to set `net.use_ssl` to true or not:
+        #
+        # https://github.com/rest-client/rest-client/blob/f450a0f086f1cd1049abbef2a2c66166a1a9ba71/lib/restclient/request.rb#L656
+        ip_as_uri = URI.parse(ip)
+        super(ip_as_uri, req, payload, &block)
+      end
+
+      def net_http_object(hostname, port)
+        super.tap do |http|
+          http.hostname_override = hostname_override if hostname_override
+        end
+      end
+
+      private
+
+      def dns_rebind_protection?
+        return false if Gitlab.http_proxy_env?
+
+        Gitlab::CurrentSettings.dns_rebinding_protection_enabled?
+      end
+
+      def allow_settings_local_requests?
+        Gitlab::CurrentSettings.allow_local_requests_from_hooks_and_services?
+      end
+    end
+
+    prepend UrlBlocker
+  end
+end