C++: Generate IR for destruction of unconditionally constructed temporaries

cpp/ql/lib/semmle/code/cpp/PrintAST.qll

@@ -364,6 +364,8 @@ class ConversionNode extends ExprNode {
     childIndex = 0 and
     result.getAst() = conv.getExpr() and
     conv.getExpr() instanceof Conversion
+    or
+    result.getAst() = expr.getImplicitDestructorCall(childIndex - 1)
   }
 }
 

cpp/ql/lib/semmle/code/cpp/exprs/Expr.qll

@@ -63,6 +63,12 @@ class Expr extends StmtParent, @expr {
    * order of destruction.
    */
   DestructorCall getImplicitDestructorCall(int n) {
+    exists(Expr e |
+      e = this.(TemporaryObjectExpr).getExpr() and
+      synthetic_destructor_call(e, max(int i | synthetic_destructor_call(e, i, _)) - n, result)
+    )
+    or
+    not this = any(TemporaryObjectExpr temp).getExpr() and
     synthetic_destructor_call(this, max(int i | synthetic_destructor_call(this, i, _)) - n, result)
   }
 

cpp/ql/lib/semmle/code/cpp/ir/implementation/raw/internal/TranslatedElement.qll

@@ -128,8 +128,10 @@ private predicate ignoreExprAndDescendants(Expr expr) {
     vaStartExpr.getLastNamedParameter().getFullyConverted() = expr
   )
   or
-  // suppress destructors of temporary variables until proper support is added for them.
-  exists(Expr parent | parent.getAnImplicitDestructorCall() = expr)
+  // Do not translate implicit destructor calls for unnamed temporary variables that are
+  // conditionally constructed (until we have a mechanism for calling these only when the
+  // temporary's constructor was run)
+  isConditionalTemporaryDestructorCall(expr)
 }
 
 /**
@@ -255,6 +257,39 @@ private predicate usedAsCondition(Expr expr) {
   )
 }
 
+private predicate hasThrowingChild(Expr e) {
+  e = any(ThrowExpr throw).getFullyConverted()
+  or
+  exists(Expr child |
+    e = getRealParent(child) and
+    hasThrowingChild(child)
+  )
+}
+
+private predicate isInConditionalEvaluation(Expr e) {
+  exists(ConditionalExpr cond |
+    e = cond.getThen().getFullyConverted() and not cond.isTwoOperand()
+    or
+    e = cond.getElse().getFullyConverted()
+    or
+    // If one of the operands throws then the temporaries constructed in either
+    // branch will also be attached to the ternary expression. We suppress
+    // those destructor calls as well.
+    hasThrowingChild([cond.getThen(), cond.getElse()]) and
+    e = cond.getFullyConverted()
+  )
+  or
+  e = any(LogicalAndExpr lae).getRightOperand().getFullyConverted()
+  or
+  e = any(LogicalOrExpr loe).getRightOperand().getFullyConverted()
+  or
+  isInConditionalEvaluation(getRealParent(e))
+}
+
+private predicate isConditionalTemporaryDestructorCall(DestructorCall dc) {
+  isInConditionalEvaluation(dc.getQualifier().(ReuseExpr).getReusedExpr())
+}
+
 /**
  * Holds if `conv` is an `InheritanceConversion` that requires a `TranslatedLoad`, despite not being
  * marked as having an lvalue-to-rvalue conversion.
@@ -783,6 +818,16 @@ newtype TTranslatedElement =
     not ignoreSideEffects(expr) and
     opcode = getCallSideEffectOpcode(expr)
   } or
+  // The set of destructors to invoke after a `throw`. These need to be special
+  // cased because the edge kind following a throw is an `ExceptionEdge`, and
+  // we need to make sure that the edge kind is still an `ExceptionEdge` after
+  // all the destructors have run.
+  TTranslatedDestructorsAfterThrow(ThrowExpr throw) {
+    exists(DestructorCall dc |
+      dc = throw.getAnImplicitDestructorCall() and
+      not ignoreExpr(dc)
+    )
+  } or
   // A precise side effect of an argument to a `Call`
   TTranslatedArgumentExprSideEffect(Call call, Expr expr, int n, SideEffectOpcode opcode) {
     not ignoreExpr(expr) and

cpp/ql/lib/semmle/code/cpp/ir/implementation/raw/internal/TranslatedExpr.qll

@@ -90,10 +90,26 @@ abstract class TranslatedExpr extends TranslatedElement {
   final override TranslatedElement getChild(int id) {
     result = this.getChildInternal(id)
     or
-    exists(int maxChildId, int destructorIndex |
-      maxChildId = max(int childId | exists(this.getChildInternal(childId))) and
-      result.(TranslatedExpr).getExpr() = expr.getImplicitDestructorCall(destructorIndex) and
-      id = maxChildId + 1 + destructorIndex
+    exists(int destructorIndex |
+      result = this.getImplicitDestructorCall(destructorIndex) and
+      id = this.getFirstDestructorCallIndex() + destructorIndex
+    )
+  }
+
+  final private TranslatedExpr getImplicitDestructorCall(int index) {
+    result.getExpr() = expr.getImplicitDestructorCall(index)
+  }
+
+  final override predicate hasAnImplicitDestructorCall() {
+    exists(this.getImplicitDestructorCall(_))
+  }
+
+  final override int getFirstDestructorCallIndex() {
+    not this.handlesDestructorsExplicitly() and
+    (
+      result = max(int childId | exists(this.getChildInternal(childId))) + 1
+      or
+      not exists(this.getChildInternal(_)) and result = 0
     )
   }
 
@@ -395,6 +411,14 @@ class TranslatedLoad extends TranslatedValueCategoryAdjustment, TTranslatedLoad
       result = this.getOperand().getResult()
     )
   }
+
+  override predicate handlesDestructorsExplicitly() {
+    // The class that generates IR for `e` will (implicitly or explicitly)
+    // handle the generation of destructor calls for `e`. Without disabling
+    // destructor call generation here the destructor will get multiple
+    // parents.
+    any()
+  }
 }
 
 /**
@@ -1999,6 +2023,13 @@ abstract class TranslatedAllocationSize extends TranslatedExpr, TTranslatedAlloc
   final override predicate producesExprResult() { none() }
 
   final override Instruction getResult() { result = this.getInstruction(AllocationSizeTag()) }
+
+  final override predicate handlesDestructorsExplicitly() {
+    // Since the enclosing `TranslatedNewOrNewArrayExpr` (implicitly) handles the destructors
+    // we need to disable the implicit handling here as otherwise the destructors will have
+    // multiple parents
+    any()
+  }
 }
 
 TranslatedAllocationSize getTranslatedAllocationSize(NewOrNewArrayExpr newExpr) {
@@ -2156,6 +2187,13 @@ class TranslatedAllocatorCall extends TTranslatedAllocatorCall, TranslatedDirect
 
   final override predicate producesExprResult() { none() }
 
+  final override predicate handlesDestructorsExplicitly() {
+    // Since the enclosing `TranslatedNewOrNewArrayExpr` (implicitly) handles the destructors
+    // we need to disable the implicit handling here as otherwise the destructors will have
+    // multiple parents
+    any()
+  }
+
   override Function getInstructionFunction(InstructionTag tag) {
     tag = CallTargetTag() and result = expr.getAllocator()
   }
@@ -2817,6 +2855,68 @@ class TranslatedReuseExpr extends TranslatedNonConstantExpr {
   }
 }
 
+/**
+ * The IR translation of the destructor calls of the parent `TranslatedThrow`.
+ *
+ * This object does not itself generate the destructor calls. Instead, its
+ * children provide the actual calls, and this object ensures that we correctly
+ * exit with an `ExceptionEdge` after executing all the destructor calls.
+ */
+class TranslatedDestructorsAfterThrow extends TranslatedElement, TTranslatedDestructorsAfterThrow {
+  ThrowExpr throw;
+
+  TranslatedDestructorsAfterThrow() { this = TTranslatedDestructorsAfterThrow(throw) }
+
+  override string toString() { result = "Destructor calls after throw: " + throw }
+
+  private TranslatedCall getTranslatedImplicitDestructorCall(int id) {
+    result.getExpr() = throw.getImplicitDestructorCall(id)
+  }
+
+  override Instruction getFirstInstruction(EdgeKind kind) {
+    result = this.getChild(0).getFirstInstruction(kind)
+  }
+
+  override ThrowExpr getAst() { result = throw }
+
+  override Instruction getInstructionSuccessorInternal(InstructionTag tag, EdgeKind kind) { none() }
+
+  override TranslatedElement getChild(int id) {
+    result = this.getTranslatedImplicitDestructorCall(id)
+  }
+
+  override predicate handlesDestructorsExplicitly() { any() }
+
+  override Declaration getFunction() { result = throw.getEnclosingFunction() }
+
+  override Instruction getChildSuccessorInternal(TranslatedElement child, EdgeKind kind) {
+    exists(int id | child = this.getChild(id) |
+      // Transition to the next child, if any.
+      result = this.getChild(id + 1).getFirstInstruction(kind)
+      or
+      // And otherwise, exit this element with an exceptional edge
+      not exists(this.getChild(id + 1)) and
+      kind instanceof ExceptionEdge and
+      result = this.getParent().getExceptionSuccessorInstruction(any(GotoEdge edge))
+    )
+  }
+
+  override TranslatedElement getLastChild() {
+    result =
+      this.getTranslatedImplicitDestructorCall(max(int id |
+          exists(throw.getImplicitDestructorCall(id))
+        ))
+  }
+
+  override Instruction getALastInstructionInternal() {
+    result = this.getLastChild().getALastInstruction()
+  }
+
+  override predicate hasInstruction(Opcode opcode, InstructionTag tag, CppType resultType) {
+    none()
+  }
+}
+
 /**
  * IR translation of a `throw` expression.
  */
@@ -2831,13 +2931,22 @@ abstract class TranslatedThrowExpr extends TranslatedNonConstantExpr {
 
   override Instruction getInstructionSuccessorInternal(InstructionTag tag, EdgeKind kind) {
     tag = ThrowTag() and
-    kind instanceof ExceptionEdge and
-    result = this.getParent().getExceptionSuccessorInstruction(any(GotoEdge edge))
+    (
+      result = this.getDestructors().getFirstInstruction(kind)
+      or
+      not exists(this.getDestructors()) and
+      kind instanceof ExceptionEdge and
+      result = this.getParent().getExceptionSuccessorInstruction(any(GotoEdge edge))
+    )
   }
 
   override Instruction getResult() { none() }
 
   abstract Opcode getThrowOpcode();
+
+  override predicate handlesDestructorsExplicitly() { any() }
+
+  TranslatedDestructorsAfterThrow getDestructors() { result.getAst() = expr }
 }
 
 /**
@@ -2849,6 +2958,9 @@ class TranslatedThrowValueExpr extends TranslatedThrowExpr, TranslatedVariableIn
 
   final override TranslatedElement getChildInternal(int id) {
     result = TranslatedVariableInitialization.super.getChildInternal(id)
+    or
+    id = max(int i | exists(TranslatedVariableInitialization.super.getChildInternal(i))) + 1 and
+    result = this.getDestructors()
   }
 
   final override Instruction getChildSuccessorInternal(TranslatedElement elem, EdgeKind kind) {
@@ -2914,14 +3026,22 @@ class TranslatedThrowValueExpr extends TranslatedThrowExpr, TranslatedVariableIn
 class TranslatedReThrowExpr extends TranslatedThrowExpr {
   override ReThrowExpr expr;
 
-  override TranslatedElement getChildInternal(int id) { none() }
+  override TranslatedElement getChildInternal(int id) {
+    id = 0 and
+    result = this.getDestructors()
+  }
 
   override Instruction getFirstInstruction(EdgeKind kind) {
     result = this.getInstruction(ThrowTag()) and
     kind instanceof GotoEdge
   }
 
-  override Instruction getALastInstructionInternal() { result = this.getInstruction(ThrowTag()) }
+  override Instruction getALastInstructionInternal() {
+    result = this.getDestructors().getALastInstruction()
+    or
+    not this.hasAnImplicitDestructorCall() and
+    result = this.getInstruction(ThrowTag())
+  }
 
   override Instruction getChildSuccessorInternal(TranslatedElement child, EdgeKind kind) { none() }
 

cpp/ql/test/experimental/query-tests/Security/CWE/CWE-416/IteratorToExpiredContainer.expected

@@ -0,0 +1,14 @@
+| test.cpp:680:30:680:30 | call to operator[] | This object is destroyed before $@ is called. | test.cpp:680:17:680:17 | call to begin | call to begin |
+| test.cpp:680:30:680:30 | call to operator[] | This object is destroyed before $@ is called. | test.cpp:680:17:680:17 | call to end | call to end |
+| test.cpp:683:31:683:32 | call to at | This object is destroyed before $@ is called. | test.cpp:683:17:683:17 | call to begin | call to begin |
+| test.cpp:683:31:683:32 | call to at | This object is destroyed before $@ is called. | test.cpp:683:17:683:17 | call to end | call to end |
+| test.cpp:689:17:689:29 | temporary object | This object is destroyed before $@ is called. | test.cpp:689:31:689:35 | call to begin | call to begin |
+| test.cpp:689:46:689:58 | temporary object | This object is destroyed before $@ is called. | test.cpp:689:60:689:62 | call to end | call to end |
+| test.cpp:702:27:702:27 | call to operator[] | This object is destroyed before $@ is called. | test.cpp:703:19:703:23 | call to begin | call to begin |
+| test.cpp:702:27:702:27 | call to operator[] | This object is destroyed before $@ is called. | test.cpp:703:36:703:38 | call to end | call to end |
+| test.cpp:716:36:716:48 | temporary object | This object is destroyed before $@ is called. | test.cpp:716:17:716:17 | call to begin | call to begin |
+| test.cpp:716:36:716:48 | temporary object | This object is destroyed before $@ is called. | test.cpp:716:17:716:17 | call to end | call to end |
+| test.cpp:727:23:727:23 | call to operator[] | This object is destroyed before $@ is called. | test.cpp:750:17:750:17 | call to begin | call to begin |
+| test.cpp:727:23:727:23 | call to operator[] | This object is destroyed before $@ is called. | test.cpp:750:17:750:17 | call to end | call to end |
+| test.cpp:735:23:735:23 | call to operator[] | This object is destroyed before $@ is called. | test.cpp:759:17:759:17 | call to begin | call to begin |
+| test.cpp:735:23:735:23 | call to operator[] | This object is destroyed before $@ is called. | test.cpp:759:17:759:17 | call to end | call to end |

cpp/ql/test/experimental/query-tests/Security/CWE/CWE-416/test.cpp

@@ -677,10 +677,10 @@ std::vector<std::vector<int>> return_self_by_value(const std::vector<std::vector
 
 void test() {
   for (auto x : returnValue()) {} // GOOD
-  for (auto x : returnValue()[0]) {} // BAD [NOT DETECTED] (see *)
+  for (auto x : returnValue()[0]) {} // BAD
   for (auto x : external_by_value(returnValue())) {} // GOOD
   for (auto x : external_by_const_ref(returnValue())) {} // GOOD
-  for (auto x : returnValue().at(0)) {} // BAD [NOT DETECTED] (see *)
+  for (auto x : returnValue().at(0)) {} // BAD
 
   for (auto x : returnRef()) {} // GOOD
   for (auto x : returnRef()[0]) {} // GOOD
@@ -700,7 +700,7 @@ void test() {
 
   {
   auto&& v = returnValue()[0];
-  for(auto it = v.begin(); it != v.end(); ++it) {} // BAD [NOT DETECTED] (see *)
+  for(auto it = v.begin(); it != v.end(); ++it) {} // BAD
   }
 
   {
@@ -713,7 +713,7 @@ void test() {
   for(auto it = v.begin(); it != v.end(); ++it) {} // GOOD
   }
 
-  for (auto x : return_self_by_ref(returnValue())) {} // BAD [NOT DETECTED] (see *)
+  for (auto x : return_self_by_ref(returnValue())) {} // BAD
 
   for (auto x : return_self_by_value(returnValue())) {} // GOOD
 }
@@ -724,15 +724,15 @@ void iterate(const std::vector<T>& v) {
 }
 
 std::vector<int>& ref_to_first_in_returnValue_1() {
-  return returnValue()[0]; // BAD [NOT DETECTED] (see *)
+  return returnValue()[0]; // BAD
 }
 
 std::vector<int>& ref_to_first_in_returnValue_2() {
   return returnValue()[0]; // BAD [NOT DETECTED]
 }
 
 std::vector<int>& ref_to_first_in_returnValue_3() {
-  return returnValue()[0]; // BAD [NOT DETECTED] (see *)
+  return returnValue()[0]; // BAD
 }
 
 std::vector<int> first_in_returnValue_1() {