UncountedLocalVarsChecker.cpp

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//=======- UncountedLocalVarsChecker.cpp -------------------------*- C++ -*-==//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
 
#include "ASTUtils.h"
#include "DiagOutputUtils.h"
#include "PtrTypesSemantics.h"
#include "clang/AST/CXXInheritance.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/ParentMapContext.h"
#include "clang/AST/RecursiveASTVisitor.h"
#include "clang/Basic/SourceLocation.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 <optional>
 
using namespace clang;
using namespace ento;
 
namespace {
 
// FIXME: should be defined by anotations in the future
bool isRefcountedStringsHack(const VarDecl *V) {
  assert(V);
  auto safeClass = [](const std::string &className) {
    return className == "String" || className == "AtomString" ||
           className == "UniquedString" || className == "Identifier";
  };
  QualType QT = V->getType();
  auto *T = QT.getTypePtr();
  if (auto *CXXRD = T->getAsCXXRecordDecl()) {
    if (safeClass(safeGetName(CXXRD)))
      return true;
  }
  if (T->isPointerType() || T->isReferenceType()) {
    if (auto *CXXRD = T->getPointeeCXXRecordDecl()) {
      if (safeClass(safeGetName(CXXRD)))
        return true;
    }
  }
  return false;
}
 
bool isGuardedScopeEmbeddedInGuardianScope(const VarDecl *Guarded,
                                           const VarDecl *MaybeGuardian) {
  assert(Guarded);
  assert(MaybeGuardian);
 
  if (!MaybeGuardian->isLocalVarDecl())
    return false;
 
  const CompoundStmt *guardiansClosestCompStmtAncestor = nullptr;
 
  ASTContext &ctx = MaybeGuardian->getASTContext();
 
  for (DynTypedNodeList guardianAncestors = ctx.getParents(*MaybeGuardian);
       !guardianAncestors.empty();
       guardianAncestors = ctx.getParents(
           *guardianAncestors
                .begin()) // FIXME - should we handle all of the parents?
  ) {
    for (auto &guardianAncestor : guardianAncestors) {
      if (auto *CStmtParentAncestor = guardianAncestor.get<CompoundStmt>()) {
        guardiansClosestCompStmtAncestor = CStmtParentAncestor;
        break;
      }
    }
    if (guardiansClosestCompStmtAncestor)
      break;
  }
 
  if (!guardiansClosestCompStmtAncestor)
    return false;
 
  // We need to skip the first CompoundStmt to avoid situation when guardian is
  // defined in the same scope as guarded variable.
  bool HaveSkippedFirstCompoundStmt = false;
  for (DynTypedNodeList guardedVarAncestors = ctx.getParents(*Guarded);
       !guardedVarAncestors.empty();
       guardedVarAncestors = ctx.getParents(
           *guardedVarAncestors
                .begin()) // FIXME - should we handle all of the parents?
  ) {
    for (auto &guardedVarAncestor : guardedVarAncestors) {
      if (auto *CStmtAncestor = guardedVarAncestor.get<CompoundStmt>()) {
        if (!HaveSkippedFirstCompoundStmt) {
          HaveSkippedFirstCompoundStmt = true;
          continue;
        }
        if (CStmtAncestor == guardiansClosestCompStmtAncestor)
          return true;
      }
    }
  }
 
  return false;
}
 
class UncountedLocalVarsChecker
    : public Checker<check::ASTDecl<TranslationUnitDecl>> {
  BugType Bug{this,
              "Uncounted raw pointer or reference not provably backed by "
              "ref-counted variable",
              "WebKit coding guidelines"};
  mutable BugReporter *BR;
 
public:
  void checkASTDecl(const TranslationUnitDecl *TUD, AnalysisManager &MGR,
                    BugReporter &BRArg) const {
    BR = &BRArg;
 
    // The calls to checkAST* from AnalysisConsumer don't
    // visit template instantiations or lambda classes. We
    // want to visit those, so we make our own RecursiveASTVisitor.
    struct LocalVisitor : public RecursiveASTVisitor<LocalVisitor> {
      const UncountedLocalVarsChecker *Checker;
 
      TrivialFunctionAnalysis TFA;
 
      using Base = RecursiveASTVisitor<LocalVisitor>;
 
      explicit LocalVisitor(const UncountedLocalVarsChecker *Checker)
          : Checker(Checker) {
        assert(Checker);
      }
 
      bool shouldVisitTemplateInstantiations() const { return true; }
      bool shouldVisitImplicitCode() const { return false; }
 
      bool VisitVarDecl(VarDecl *V) {
        auto *Init = V->getInit();
        if (Init && V->isLocalVarDecl())
          Checker->visitVarDecl(V, Init);
        return true;
      }
 
      bool VisitBinaryOperator(const BinaryOperator *BO) {
        if (BO->isAssignmentOp()) {
          if (auto *VarRef = dyn_cast<DeclRefExpr>(BO->getLHS())) {
            if (auto *V = dyn_cast<VarDecl>(VarRef->getDecl()))
              Checker->visitVarDecl(V, BO->getRHS());
          }
        }
        return true;
      }
 
      bool TraverseIfStmt(IfStmt *IS) {
        if (!TFA.isTrivial(IS))
          return Base::TraverseIfStmt(IS);
        return true;
      }
 
      bool TraverseForStmt(ForStmt *FS) {
        if (!TFA.isTrivial(FS))
          return Base::TraverseForStmt(FS);
        return true;
      }
 
      bool TraverseCXXForRangeStmt(CXXForRangeStmt *FRS) {
        if (!TFA.isTrivial(FRS))
          return Base::TraverseCXXForRangeStmt(FRS);
        return true;
      }
 
      bool TraverseWhileStmt(WhileStmt *WS) {
        if (!TFA.isTrivial(WS))
          return Base::TraverseWhileStmt(WS);
        return true;
      }
 
      bool TraverseCompoundStmt(CompoundStmt *CS) {
        if (!TFA.isTrivial(CS))
          return Base::TraverseCompoundStmt(CS);
        return true;
      }
    };
 
    LocalVisitor visitor(this);
    visitor.TraverseDecl(const_cast<TranslationUnitDecl *>(TUD));
  }
 
  void visitVarDecl(const VarDecl *V, const Expr *Value) const {
    if (shouldSkipVarDecl(V))
      return;
 
    const auto *ArgType = V->getType().getTypePtr();
    if (!ArgType)
      return;
 
    std::optional<bool> IsUncountedPtr = isUncountedPtr(ArgType);
    if (IsUncountedPtr && *IsUncountedPtr) {
      if (tryToFindPtrOrigin(
              Value, /*StopAtFirstRefCountedObj=*/false,
              [&](const clang::Expr *InitArgOrigin, bool IsSafe) {
                if (!InitArgOrigin)
                  return true;
 
                if (isa<CXXThisExpr>(InitArgOrigin))
                  return true;
 
                if (isa<CXXNullPtrLiteralExpr>(InitArgOrigin))
                  return true;
 
                if (isa<IntegerLiteral>(InitArgOrigin))
                  return true;
 
                if (auto *Ref = llvm::dyn_cast<DeclRefExpr>(InitArgOrigin)) {
                  if (auto *MaybeGuardian =
                          dyn_cast_or_null<VarDecl>(Ref->getFoundDecl())) {
                    const auto *MaybeGuardianArgType =
                        MaybeGuardian->getType().getTypePtr();
                    if (MaybeGuardianArgType) {
                      const CXXRecordDecl *const MaybeGuardianArgCXXRecord =
                          MaybeGuardianArgType->getAsCXXRecordDecl();
                      if (MaybeGuardianArgCXXRecord) {
                        if (MaybeGuardian->isLocalVarDecl() &&
                            (isRefCounted(MaybeGuardianArgCXXRecord) ||
                             isRefcountedStringsHack(MaybeGuardian)) &&
                            isGuardedScopeEmbeddedInGuardianScope(
                                V, MaybeGuardian))
                          return true;
                      }
                    }
 
                    // Parameters are guaranteed to be safe for the duration of
                    // the call by another checker.
                    if (isa<ParmVarDecl>(MaybeGuardian))
                      return true;
                  }
                }
 
                return false;
              }))
        return;
 
      reportBug(V, Value);
    }
  }
 
  bool shouldSkipVarDecl(const VarDecl *V) const {
    assert(V);
    return BR->getSourceManager().isInSystemHeader(V->getLocation());
  }
 
  void reportBug(const VarDecl *V, const Expr *Value) const {
    assert(V);
    SmallString<100> Buf;
    llvm::raw_svector_ostream Os(Buf);
 
    if (dyn_cast<ParmVarDecl>(V)) {
      Os << "Assignment to an uncounted parameter ";
      printQuotedQualifiedName(Os, V);
      Os << " is unsafe.";
 
      PathDiagnosticLocation BSLoc(Value->getExprLoc(), BR->getSourceManager());
      auto Report = std::make_unique<BasicBugReport>(Bug, Os.str(), BSLoc);
      Report->addRange(Value->getSourceRange());
      BR->emitReport(std::move(Report));
    } else {
      if (V->hasLocalStorage())
        Os << "Local variable ";
      else if (V->isStaticLocal())
        Os << "Static local variable ";
      else if (V->hasGlobalStorage())
        Os << "Global variable ";
      else
        Os << "Variable ";
      printQuotedQualifiedName(Os, V);
      Os << " is uncounted and unsafe.";
 
      PathDiagnosticLocation BSLoc(V->getLocation(), BR->getSourceManager());
      auto Report = std::make_unique<BasicBugReport>(Bug, Os.str(), BSLoc);
      Report->addRange(V->getSourceRange());
      BR->emitReport(std::move(Report));
    }
  }
};
} // namespace
 
void ento::registerUncountedLocalVarsChecker(CheckerManager &Mgr) {
  Mgr.registerChecker<UncountedLocalVarsChecker>();
}
 
bool ento::shouldRegisterUncountedLocalVarsChecker(const CheckerManager &) {
  return true;
}