Merge pull request github#13407 from asgerf/rb/restrict-orm-tracking

Ruby: restrict ORM tracking to calls

Author: asgerf

ruby/ql/lib/codeql/ruby/security/XSS.qll

@@ -285,14 +285,22 @@ private module OrmTracking {
    * A data flow configuration to track flow from finder calls to field accesses.
    */
   private module Config implements DataFlow::ConfigSig {
-    predicate isSource(DataFlow::Node source) { source instanceof OrmInstantiation }
+    predicate isSource(DataFlow::Node source) {
+      // We currently only use ORM instances that come from a call site, so restrict the sources
+      // to calls. This works around a performance issue that would arise from using 'self' as a source
+      // in ActiveRecord models. Over time, library models should stop relying on OrmInstantiation and instead
+      // use API graphs or type-tracking the same way we track other types.
+      source instanceof OrmInstantiation and source instanceof DataFlow::CallNode
+    }
 
     // Select any call receiver and narrow down later
     predicate isSink(DataFlow::Node sink) { sink = any(DataFlow::CallNode c).getReceiver() }
 
     predicate isAdditionalFlowStep(DataFlow::Node node1, DataFlow::Node node2) {
       Shared::isAdditionalXssFlowStep(node1, node2)
     }
+
+    predicate isBarrierIn(DataFlow::Node node) { node instanceof DataFlow::SelfParameterNode }
   }
 
   import DataFlow::Global<Config>