Ruby: use InstanceVariableRead/WriteAccess CFG nodes

Author: aibaars

ruby/ql/lib/codeql/ruby/controlflow/CfgNodes.qll

@@ -623,7 +623,7 @@ module ExprNodes {
   class InstanceVariableAccessCfgNode extends ExprCfgNode {
     override InstanceVariableAccessMapping e;
 
-    final override InstanceVariableAccess getExpr() { result = ExprCfgNode.super.getExpr() }
+    override InstanceVariableAccess getExpr() { result = ExprCfgNode.super.getExpr() }
 
     /**
      * Gets the synthetic receiver(`self`) of this instance variable access.
@@ -652,11 +652,22 @@ module ExprNodes {
     final override ConstantWriteAccess getExpr() { result = ExprCfgNode.super.getExpr() }
   }
 
+  /** A control-flow node that wraps an `InstanceVariableReadAccess` AST expression. */
+  class InstanceVariableReadAccessCfgNode extends InstanceVariableAccessCfgNode {
+    InstanceVariableReadAccessCfgNode() { this.getNode() instanceof InstanceVariableReadAccess }
+
+    final override InstanceVariableReadAccess getExpr() {
+      result = InstanceVariableAccessCfgNode.super.getExpr()
+    }
+  }
+
   /** A control-flow node that wraps an `InstanceVariableWriteAccess` AST expression. */
-  class InstanceVariableWriteAccessCfgNode extends ExprCfgNode {
-    override InstanceVariableWriteAccess e;
+  class InstanceVariableWriteAccessCfgNode extends InstanceVariableAccessCfgNode {
+    InstanceVariableWriteAccessCfgNode() { this.getNode() instanceof InstanceVariableWriteAccess }
 
-    final override InstanceVariableWriteAccess getExpr() { result = ExprCfgNode.super.getExpr() }
+    final override InstanceVariableWriteAccess getExpr() {
+      result = InstanceVariableAccessCfgNode.super.getExpr()
+    }
   }
 
   /** A control-flow node that wraps a `StringInterpolationComponent` AST expression. */

ruby/ql/lib/codeql/ruby/dataflow/internal/DataFlowPrivate.qll

@@ -794,8 +794,7 @@ predicate jumpStep(Node pred, Node succ) {
 predicate storeStep(Node node1, ContentSet c, Node node2) {
   // Instance variable assignment, `@var = src`
   node2.(PostUpdateNode).getPreUpdateNode().asExpr() =
-    any(CfgNodes::ExprNodes::InstanceVariableAccessCfgNode var |
-      var.getExpr() instanceof InstanceVariableWriteAccess and
+    any(CfgNodes::ExprNodes::InstanceVariableWriteAccessCfgNode var |
       exists(CfgNodes::ExprNodes::AssignExprCfgNode assign |
         var = assign.getLhs() and
         node1.asExpr() = assign.getRhs()
@@ -815,8 +814,7 @@ predicate storeStep(Node node1, ContentSet c, Node node2) {
 predicate readStep(Node node1, ContentSet c, Node node2) {
   // Instance variable read access, `@var`
   node2.asExpr() =
-    any(CfgNodes::ExprNodes::InstanceVariableAccessCfgNode var |
-      var.getExpr() instanceof InstanceVariableReadAccess and
+    any(CfgNodes::ExprNodes::InstanceVariableReadAccessCfgNode var |
       node1.asExpr() = var.getReceiver() and
       c.isSingleton(any(Content::FieldContent ct |
           ct.getName() = var.getExpr().getVariable().getName()