[webkit.RefCntblBaseVirtualDtor] Allow CRTP classes without a virtual destructor. (#92837)

Exempt CRTP (Curiously Recurring Template Pattern) classes with a delete
operation acting on "this" pointer with an appropriate cast from the
requirement that a ref-countable superclass must have a virtual
destructor.

To do this, this PR introduces new DerefFuncDeleteExprVisitor, which
looks for a delete operation with an explicit cast to the derived class
in a base class.

This PR also changes the checker so that we only check a given class's
immediate base class instead of all ancestor base classes in the class
hierarchy. This is sufficient because the checker will eventually see
the definition for every class in the class hierarchy and transitively
proves every ref-counted base class has a virtual destructor or deref
function which casts this pointer back to the derived class before
deleting. Without this change, we would keep traversing the same list of
base classes whenever we encounter a new subclass, which is wholly
unnecessary.

It's possible for DerefFuncDeleteExprVisitor to come to a conclusoin that
there isn't enough information to determine whether a given templated
superclass invokes delete operation on a subclass when the template
isn't fully specialized for the subclass. In this case, we return
std::nullopt in HasSpecializedDelete, and visitCXXRecordDecl will skip
this declaration. This is okay because the checker will eventually see a
concreate fully specialized class definition if it ever gets
instantiated.

Author: rniwa

clang/lib/StaticAnalyzer/Checkers/WebKit/RefCntblBaseVirtualDtorChecker.cpp

@@ -11,16 +11,116 @@
 #include "PtrTypesSemantics.h"
 #include "clang/AST/CXXInheritance.h"
 #include "clang/AST/RecursiveASTVisitor.h"
+#include "clang/AST/StmtVisitor.h"
 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
 #include "clang/StaticAnalyzer/Core/BugReporter/BugReporter.h"
 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
 #include "clang/StaticAnalyzer/Core/Checker.h"
+#include "llvm/ADT/DenseSet.h"
+#include "llvm/ADT/SetVector.h"
 #include <optional>
 
 using namespace clang;
 using namespace ento;
 
 namespace {
+
+class DerefFuncDeleteExprVisitor
+    : public ConstStmtVisitor<DerefFuncDeleteExprVisitor, bool> {
+  // Returns true if any of child statements return true.
+  bool VisitChildren(const Stmt *S) {
+    for (const Stmt *Child : S->children()) {
+      if (Child && Visit(Child))
+        return true;
+    }
+    return false;
+  }
+
+  bool VisitBody(const Stmt *Body) {
+    if (!Body)
+      return false;
+
+    auto [It, IsNew] = VisitedBody.insert(Body);
+    if (!IsNew) // This body is recursive
+      return false;
+
+    return Visit(Body);
+  }
+
+public:
+  DerefFuncDeleteExprVisitor(const TemplateArgumentList &ArgList,
+                             const CXXRecordDecl *ClassDecl)
+      : ArgList(&ArgList), ClassDecl(ClassDecl) {}
+
+  DerefFuncDeleteExprVisitor(const CXXRecordDecl *ClassDecl)
+      : ClassDecl(ClassDecl) {}
+
+  std::optional<bool> HasSpecializedDelete(CXXMethodDecl *Decl) {
+    if (auto *Body = Decl->getBody())
+      return VisitBody(Body);
+    if (auto *Tmpl = Decl->getTemplateInstantiationPattern())
+      return std::nullopt; // Indeterminate. There was no concrete instance.
+    return false;
+  }
+
+  bool VisitCallExpr(const CallExpr *CE) {
+    const Decl *D = CE->getCalleeDecl();
+    if (D && D->hasBody())
+      return VisitBody(D->getBody());
+    return false;
+  }
+
+  bool VisitCXXDeleteExpr(const CXXDeleteExpr *E) {
+    auto *Arg = E->getArgument();
+    while (Arg) {
+      if (auto *Paren = dyn_cast<ParenExpr>(Arg))
+        Arg = Paren->getSubExpr();
+      else if (auto *Cast = dyn_cast<CastExpr>(Arg)) {
+        Arg = Cast->getSubExpr();
+        auto CastType = Cast->getType();
+        if (auto *PtrType = dyn_cast<PointerType>(CastType)) {
+          auto PointeeType = PtrType->getPointeeType();
+          while (auto *ET = dyn_cast<ElaboratedType>(PointeeType)) {
+            if (ET->isSugared())
+              PointeeType = ET->desugar();
+          }
+          if (auto *ParmType = dyn_cast<TemplateTypeParmType>(PointeeType)) {
+            if (ArgList) {
+              auto ParmIndex = ParmType->getIndex();
+              auto Type = ArgList->get(ParmIndex).getAsType();
+              if (Type->getAsCXXRecordDecl() == ClassDecl)
+                return true;
+            }
+          } else if (auto *RD = dyn_cast<RecordType>(PointeeType)) {
+            if (RD->getDecl() == ClassDecl)
+              return true;
+          } else if (auto *ST =
+                         dyn_cast<SubstTemplateTypeParmType>(PointeeType)) {
+            auto Type = ST->getReplacementType();
+            if (auto *RD = dyn_cast<RecordType>(Type)) {
+              if (RD->getDecl() == ClassDecl)
+                return true;
+            }
+          }
+        }
+      } else
+        break;
+    }
+    return false;
+  }
+
+  bool VisitStmt(const Stmt *S) { return VisitChildren(S); }
+
+  // Return false since the contents of lambda isn't necessarily executed.
+  // If it is executed, VisitCallExpr above will visit its body.
+  bool VisitLambdaExpr(const LambdaExpr *) { return false; }
+
+private:
+  const TemplateArgumentList *ArgList{nullptr};
+  const CXXRecordDecl *ClassDecl;
+  llvm::DenseSet<const Stmt *> VisitedBody;
+};
+
 class RefCntblBaseVirtualDtorChecker
     : public Checker<check::ASTDecl<TranslationUnitDecl>> {
 private:
@@ -51,92 +151,136 @@ class RefCntblBaseVirtualDtorChecker
       bool shouldVisitImplicitCode() const { return false; }
 
       bool VisitCXXRecordDecl(const CXXRecordDecl *RD) {
-        Checker->visitCXXRecordDecl(RD);
+        if (!RD->hasDefinition())
+          return true;
+
+        Decls.insert(RD);
+
+        for (auto &Base : RD->bases()) {
+          const auto AccSpec = Base.getAccessSpecifier();
+          if (AccSpec == AS_protected || AccSpec == AS_private ||
+              (AccSpec == AS_none && RD->isClass()))
+            continue;
+
+          QualType T = Base.getType();
+          if (T.isNull())
+            continue;
+
+          const CXXRecordDecl *C = T->getAsCXXRecordDecl();
+          if (!C)
+            continue;
+
+          if (auto *CTSD = dyn_cast<ClassTemplateSpecializationDecl>(C)) {
+            for (auto &Arg : CTSD->getTemplateArgs().asArray()) {
+              if (Arg.getKind() != TemplateArgument::Type)
+                continue;
+              auto TemplT = Arg.getAsType();
+              if (TemplT.isNull())
+                continue;
+
+              bool IsCRTP = TemplT->getAsCXXRecordDecl() == RD;
+              if (!IsCRTP)
+                continue;
+              CRTPs.insert(C);
+            }
+          }
+        }
+
         return true;
       }
+
+      llvm::SetVector<const CXXRecordDecl *> Decls;
+      llvm::DenseSet<const CXXRecordDecl *> CRTPs;
     };
 
     LocalVisitor visitor(this);
     visitor.TraverseDecl(const_cast<TranslationUnitDecl *>(TUD));
+    for (auto *RD : visitor.Decls) {
+      if (visitor.CRTPs.contains(RD))
+        continue;
+      visitCXXRecordDecl(RD);
+    }
   }
 
   void visitCXXRecordDecl(const CXXRecordDecl *RD) const {
     if (shouldSkipDecl(RD))
       return;
 
-    CXXBasePaths Paths;
-    Paths.setOrigin(RD);
+    for (auto &Base : RD->bases()) {
+      const auto AccSpec = Base.getAccessSpecifier();
+      if (AccSpec == AS_protected || AccSpec == AS_private ||
+          (AccSpec == AS_none && RD->isClass()))
+        continue;
 
-    const CXXBaseSpecifier *ProblematicBaseSpecifier = nullptr;
-    const CXXRecordDecl *ProblematicBaseClass = nullptr;
+      auto hasRefInBase = clang::hasPublicMethodInBase(&Base, "ref");
+      auto hasDerefInBase = clang::hasPublicMethodInBase(&Base, "deref");
 
-    const auto IsPublicBaseRefCntblWOVirtualDtor =
-        [RD, &ProblematicBaseSpecifier,
-         &ProblematicBaseClass](const CXXBaseSpecifier *Base, CXXBasePath &) {
-          const auto AccSpec = Base->getAccessSpecifier();
-          if (AccSpec == AS_protected || AccSpec == AS_private ||
-              (AccSpec == AS_none && RD->isClass()))
-            return false;
+      bool hasRef = hasRefInBase && *hasRefInBase != nullptr;
+      bool hasDeref = hasDerefInBase && *hasDerefInBase != nullptr;
 
-          auto hasRefInBase = clang::hasPublicMethodInBase(Base, "ref");
-          auto hasDerefInBase = clang::hasPublicMethodInBase(Base, "deref");
+      QualType T = Base.getType();
+      if (T.isNull())
+        continue;
 
-          bool hasRef = hasRefInBase && *hasRefInBase != nullptr;
-          bool hasDeref = hasDerefInBase && *hasDerefInBase != nullptr;
+      const CXXRecordDecl *C = T->getAsCXXRecordDecl();
+      if (!C)
+        continue;
 
-          QualType T = Base->getType();
-          if (T.isNull())
-            return false;
-
-          const CXXRecordDecl *C = T->getAsCXXRecordDecl();
-          if (!C)
-            return false;
-          if (isRefCountedClass(C))
-            return false;
-
-          bool AnyInconclusiveBase = false;
-          const auto hasPublicRefInBase =
-              [&AnyInconclusiveBase](const CXXBaseSpecifier *Base,
-                                     CXXBasePath &) {
-                auto hasRefInBase = clang::hasPublicMethodInBase(Base, "ref");
-                if (!hasRefInBase) {
-                  AnyInconclusiveBase = true;
-                  return false;
-                }
-                return (*hasRefInBase) != nullptr;
-              };
-          const auto hasPublicDerefInBase = [&AnyInconclusiveBase](
-                                                const CXXBaseSpecifier *Base,
-                                                CXXBasePath &) {
+      bool AnyInconclusiveBase = false;
+      const auto hasPublicRefInBase =
+          [&AnyInconclusiveBase](const CXXBaseSpecifier *Base, CXXBasePath &) {
+            auto hasRefInBase = clang::hasPublicMethodInBase(Base, "ref");
+            if (!hasRefInBase) {
+              AnyInconclusiveBase = true;
+              return false;
+            }
+            return (*hasRefInBase) != nullptr;
+          };
+      const auto hasPublicDerefInBase =
+          [&AnyInconclusiveBase](const CXXBaseSpecifier *Base, CXXBasePath &) {
             auto hasDerefInBase = clang::hasPublicMethodInBase(Base, "deref");
             if (!hasDerefInBase) {
               AnyInconclusiveBase = true;
               return false;
             }
             return (*hasDerefInBase) != nullptr;
           };
-          CXXBasePaths Paths;
-          Paths.setOrigin(C);
-          hasRef = hasRef || C->lookupInBases(hasPublicRefInBase, Paths,
+      CXXBasePaths Paths;
+      Paths.setOrigin(C);
+      hasRef = hasRef || C->lookupInBases(hasPublicRefInBase, Paths,
+                                          /*LookupInDependent =*/true);
+      hasDeref = hasDeref || C->lookupInBases(hasPublicDerefInBase, Paths,
                                               /*LookupInDependent =*/true);
-          hasDeref = hasDeref || C->lookupInBases(hasPublicDerefInBase, Paths,
-                                                  /*LookupInDependent =*/true);
-          if (AnyInconclusiveBase || !hasRef || !hasDeref)
-            return false;
-
-          const auto *Dtor = C->getDestructor();
-          if (!Dtor || !Dtor->isVirtual()) {
-            ProblematicBaseSpecifier = Base;
-            ProblematicBaseClass = C;
-            return true;
-          }
-
-          return false;
-        };
-
-    if (RD->lookupInBases(IsPublicBaseRefCntblWOVirtualDtor, Paths,
-                          /*LookupInDependent =*/true)) {
-      reportBug(RD, ProblematicBaseSpecifier, ProblematicBaseClass);
+      if (AnyInconclusiveBase || !hasRef || !hasDeref)
+        continue;
+
+      auto HasSpecializedDelete = isClassWithSpecializedDelete(C, RD);
+      if (!HasSpecializedDelete || *HasSpecializedDelete)
+        continue;
+      if (C->lookupInBases(
+              [&](const CXXBaseSpecifier *Base, CXXBasePath &) {
+                auto *T = Base->getType().getTypePtrOrNull();
+                if (!T)
+                  return false;
+                auto *R = T->getAsCXXRecordDecl();
+                if (!R)
+                  return false;
+                auto Result = isClassWithSpecializedDelete(R, RD);
+                if (!Result)
+                  AnyInconclusiveBase = true;
+                return Result && *Result;
+              },
+              Paths, /*LookupInDependent =*/true))
+        continue;
+      if (AnyInconclusiveBase)
+        continue;
+
+      const auto *Dtor = C->getDestructor();
+      if (!Dtor || !Dtor->isVirtual()) {
+        auto *ProblematicBaseSpecifier = &Base;
+        auto *ProblematicBaseClass = C;
+        reportBug(RD, ProblematicBaseSpecifier, ProblematicBaseClass);
+      }
     }
   }
 
@@ -182,6 +326,32 @@ class RefCntblBaseVirtualDtorChecker
             ClsName == "ThreadSafeRefCountedAndCanMakeThreadSafeWeakPtr");
   }
 
+  static std::optional<bool>
+  isClassWithSpecializedDelete(const CXXRecordDecl *C,
+                               const CXXRecordDecl *DerivedClass) {
+    if (auto *ClsTmplSpDecl = dyn_cast<ClassTemplateSpecializationDecl>(C)) {
+      for (auto *MethodDecl : C->methods()) {
+        if (safeGetName(MethodDecl) == "deref") {
+          DerefFuncDeleteExprVisitor Visitor(ClsTmplSpDecl->getTemplateArgs(),
+                                             DerivedClass);
+          auto Result = Visitor.HasSpecializedDelete(MethodDecl);
+          if (!Result || *Result)
+            return Result;
+        }
+      }
+      return false;
+    }
+    for (auto *MethodDecl : C->methods()) {
+      if (safeGetName(MethodDecl) == "deref") {
+        DerefFuncDeleteExprVisitor Visitor(DerivedClass);
+        auto Result = Visitor.HasSpecializedDelete(MethodDecl);
+        if (!Result || *Result)
+          return Result;
+      }
+    }
+    return false;
+  }
+
   void reportBug(const CXXRecordDecl *DerivedClass,
                  const CXXBaseSpecifier *BaseSpec,
                  const CXXRecordDecl *ProblematicBaseClass) const {

clang/test/Analysis/Checkers/WebKit/ref-cntbl-base-virtual-dtor-ref-deref-on-diff-classes.cpp

@@ -19,4 +19,5 @@ struct Derived : Base { };
 
 void foo () {
   Derived d;
+  d.deref();
 }