JS: Add TypeTracker library

javascript/ql/src/semmle/javascript/dataflow/DataFlow.qll

@@ -1221,4 +1221,5 @@ module DataFlow {
   import TypeInference
   import Configuration
   import TrackedNodes
+  import TypeTracking
 }

javascript/ql/src/semmle/javascript/dataflow/Sources.qll

@@ -7,6 +7,7 @@
  */
 
 import javascript
+private import semmle.javascript.dataflow.TypeTracking
 
 /**
  * A source node for local data flow, that is, a node from which local data flow is tracked.
@@ -153,6 +154,25 @@ class SourceNode extends DataFlow::Node {
   DataFlow::SourceNode getAPropertySource(string prop) {
     result.flowsTo(getAPropertyWrite(prop).getRhs())
   }
+
+  /**
+   * Gets a node that this node may flow to using one heap and/or interprocedural step.
+   *
+   * See `TypeTracker` for more details about how to use this.
+   */
+  DataFlow::SourceNode track(TypeTracker src, TypeTracker dst) {
+    exists(StepSummary summary |
+      StepSummary::step(this, result, summary) and
+      dst = StepSummary::append(src, summary)
+    )
+  }
+
+  /**
+   * Gets a node that may flow into this one using one heap and/or interprocedural step.
+   *
+   * See `TypeTracker` for more details about how to use this.
+   */
+  DataFlow::SourceNode backtrack(TypeTracker src, TypeTracker dst) { this = result.track(src, dst) }
 }
 
 module SourceNode {

javascript/ql/src/semmle/javascript/dataflow/TrackedNodes.qll

@@ -4,6 +4,7 @@
  */
 
 import javascript
+private import internal.FlowSteps as FlowSteps
 
 /**
  * A data flow node that should be tracked inter-procedurally.

javascript/ql/src/semmle/javascript/dataflow/TypeTracking.qll

@@ -0,0 +1,180 @@
+/**
+ * Provides the `TypeTracker` class for tracking types interprocedurally.
+ *
+ * This provides an alternative to `DataFlow::TrackedNode` and `AbstractValue`
+ * for tracking certain types interprocedurally without computing which source
+ * a given value came from.
+ */
+
+import javascript
+private import internal.FlowSteps
+
+/**
+ * A pair of booleans, indicating whether a path goes through a return and/or a call.
+ *
+ * Identical to `TPathSummary` except without flow labels.
+ */
+private newtype TStepSummary = MkStepSummary(boolean hasReturn, boolean hasCall) {
+  (hasReturn = true or hasReturn = false) and
+  (hasCall = true or hasCall = false)
+}
+
+/**
+ * Summary of the steps needed to track a value to a given dataflow node.
+ */
+class StepSummary extends TStepSummary {
+  Boolean hasReturn;
+
+  Boolean hasCall;
+
+  StepSummary() { this = MkStepSummary(hasReturn, hasCall) }
+
+  /** Indicates whether the path represented by this summary contains any return steps. */
+  boolean hasReturn() { result = hasReturn }
+
+  /** Indicates whether the path represented by this summary contains any call steps. */
+  boolean hasCall() { result = hasCall }
+
+  /**
+   * Gets the summary for the path obtained by appending `that` to `this`.
+   *
+   * Note that a path containing a `return` step cannot be appended to a path containing
+   * a `call` step in order to maintain well-formedness.
+   */
+  StepSummary append(StepSummary that) {
+    exists(Boolean hasReturn2, Boolean hasCall2 |
+      that = MkStepSummary(hasReturn2, hasCall2)
+    |
+      result = MkStepSummary(hasReturn.booleanOr(hasReturn2), hasCall.booleanOr(hasCall2)) and
+      // avoid constructing invalid paths
+      not (hasCall = true and hasReturn2 = true)
+    )
+  }
+
+  /**
+   * Gets the summary for the path obtained by appending `this` to `that`.
+   */
+  StepSummary prepend(StepSummary that) { result = that.append(this) }
+
+  /** Gets a textual representation of this path summary. */
+  string toString() {
+    exists(string withReturn, string withCall |
+      (if hasReturn = true then withReturn = "with" else withReturn = "without") and
+      (if hasCall = true then withCall = "with" else withCall = "without")
+    |
+      result = "path " + withReturn + " return steps and " + withCall + " call steps"
+    )
+  }
+}
+
+module StepSummary {
+  /**
+   * Gets a summary describing a path without any calls or returns.
+   */
+  StepSummary level() { result = MkStepSummary(false, false) }
+
+  /**
+   * Gets a summary describing a path with one or more calls, but no returns.
+   */
+  StepSummary call() { result = MkStepSummary(false, true) }
+
+  /**
+   * Gets a summary describing a path with one or more returns, but no calls.
+   */
+  StepSummary return() { result = MkStepSummary(true, false) }
+
+  /**
+   * INTERNAL: Use `SourceNode.track()` instead.
+   */
+  predicate step(DataFlow::SourceNode pred, DataFlow::SourceNode succ, StepSummary summary) {
+    exists (DataFlow::Node predNode | pred.flowsTo(predNode) |
+      // Flow through properties of objects
+      propertyFlowStep(predNode, succ) and
+      summary = level()
+      or
+      // Flow through global variables
+      globalFlowStep(predNode, succ) and
+      summary = level()
+      or
+      // Flow into function
+      callStep(predNode, succ) and
+      summary = call()
+      or
+      // Flow out of function
+      returnStep(predNode, succ) and
+      summary = return()
+    )
+    or
+    DataFlow::localFieldStep(pred, succ) and
+    summary = level()
+  }
+
+  /**
+   * INTERNAL. Do not use.
+   *
+   * Appends a step summary onto a type-tracking summary.
+   */
+  TypeTracker append(TypeTracker type, StepSummary summary) {
+    not (type.hasCall() = true and summary.hasReturn() = true) and
+    result.hasCall() = type.hasCall().booleanOr(summary.hasCall())
+  }
+}
+
+private newtype TTypeTracker = MkTypeTracker(boolean hasCall) {
+  hasCall = true or hasCall = false
+}
+
+/**
+ * Summary of the steps needed to track a value to a given dataflow node.
+ *
+ * This can be used to track objects that implement a certain API in order to
+ * recognize calls to that API. Note that type-tracking does not provide a
+ * source/sink relation, that is, it may determine that a node has a given type,
+ * but it won't determine where that type came from.
+ *
+ * It is recommended that all uses of this type is written on the following form,
+ * for tracking some type `myType`:
+ * ```
+ * DataFlow::SourceNode myType(DataFlow::TypeTracker t) {
+ *   t.start() and
+ *   result = < source of myType >
+ *   or
+ *   exists (DataFlow::TypeTracker t2 |
+ *     result = myType(t2).track(t2, t)
+ *   )
+ * }
+ *
+ * DataFlow::SourceNode myType() { result = myType(_) }
+ * ```
+ *
+ * This class can also be used to track values backwards, which can be useful for tracking
+ * the type of a callback. To do so, use the example above except with `.track`
+ * replaced with `.backtrack`.
+ */
+class TypeTracker extends TTypeTracker {
+  Boolean hasCall;
+
+  TypeTracker() { this = MkTypeTracker(hasCall) }
+
+  string toString() {
+    hasCall = true and result = "type tracker with call steps"
+    or
+    hasCall = false and result = "type tracker without call steps"
+  }
+
+  /**
+   * Holds if this is the starting point of type tracking.
+   */
+  predicate start() {
+    hasCall = false
+  }
+
+  /**
+   * INTERNAL. DO NOT USE.
+   *
+   * Holds if this type has been tracked into a call.
+   */
+  boolean hasCall() {
+    result = hasCall
+  }
+}