Cpp: Replace sink inlining with a forward scan from source.

Author: aschackmull

cpp/ql/lib/semmle/code/cpp/security/InvalidPointerDereference/InvalidPointerToDereference.qll

@@ -160,6 +160,26 @@ private module InvalidPointerToDerefBarrier {
   }
 }
 
+/**
+ * BEWARE: This configuration uses an unrestricted sink, so accessing its full
+ * flow computation or any stages beyond the first 2 will likely diverge.
+ * Stage 1 will still be fast and we use it to restrict the subsequent sink
+ * computation.
+ */
+private module InvalidPointerReachesConfig implements DataFlow::ConfigSig {
+  predicate isSource(DataFlow::Node source) { invalidPointerToDerefSource(_, _, source) }
+
+  predicate isSink(DataFlow::Node sink) { any() }
+
+  predicate isBarrier(DataFlow::Node node) { InvalidPointerToDerefConfig::isBarrier(node) }
+
+  int fieldFlowBranchLimit() { result = invalidPointerToDereferenceFieldFlowBranchLimit() }
+}
+
+private module InvalidPointerReachesFlow = DataFlow::Global<InvalidPointerReachesConfig>;
+
+private import semmle.code.cpp.ir.dataflow.internal.DataFlowImplCommon as DataFlowImplCommon
+
 /**
  * A configuration to track flow from a pointer-arithmetic operation found
  * by `AllocToInvalidPointerConfig` to a dereference of the pointer.
@@ -173,8 +193,13 @@ private module InvalidPointerToDerefConfig implements DataFlow::StateConfigSig {
     invalidPointerToDerefSource(_, pai, source)
   }
 
-  pragma[inline]
-  predicate isSink(DataFlow::Node sink) { isInvalidPointerDerefSink(sink, _, _, _, _) }
+  predicate isSink(DataFlow::Node sink) {
+    exists(DataFlowImplCommon::NodeEx n |
+      InvalidPointerReachesFlow::Stages::Stage1::sinkNode(n, _) and
+      n.asNode() = sink and
+      isInvalidPointerDerefSink(sink, _, _, _, _)
+    )
+  }
 
   predicate isSink(DataFlow::Node sink, FlowState pai) { none() }
 

shared/dataflow/codeql/dataflow/internal/DataFlowImpl.qll

@@ -2773,8 +2773,6 @@ module MakeImpl<LocationSig Location, InputSig<Location> Lang> {
         }
 
         /**
-         * INTERNAL: Only for debugging.
-         *
          * Provides a graph representation of the data flow in this stage suitable for use in a `path-problem` query.
          */
         additional module Graph {
@@ -4634,6 +4632,8 @@ module MakeImpl<LocationSig Location, InputSig<Location> Lang> {
      */
     predicate stageStats = Debug::stageStats/10;
 
+    private module Stage1alias = Stage1;
+
     private module Stage2alias = Stage2;
 
     private module Stage3alias = Stage3;
@@ -4643,18 +4643,29 @@ module MakeImpl<LocationSig Location, InputSig<Location> Lang> {
     private module Stage5alias = Stage5;
 
     /**
-     * INTERNAL: Only for debugging.
+     * INTERNAL: Subject to change without notice.
      *
      * Contains references to individual pruning stages.
      */
-    module Debug {
+    module Stages {
+      module Stage1 = Stage1alias;
+
       module Stage2 = Stage2alias;
 
       module Stage3 = Stage3alias;
 
       module Stage4 = Stage4alias;
 
       module Stage5 = Stage5alias;
+    }
+
+    /**
+     * INTERNAL: Only for debugging.
+     *
+     * Contains references to individual pruning stages and stage statistics.
+     */
+    module Debug {
+      import Stages
 
       predicate stageStats1(
         int n, string stage, int nodes, int fields, int conscand, int states, int tuples,