text: //=== CastToStructChecker.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
  //
  //===----------------------------------------------------------------------===//
  //
  // This files defines CastToStructChecker, a builtin checker that checks for
  // cast from non-struct pointer to struct pointer and widening struct data cast.
  // This check corresponds to CWE-588.
  //
  //===----------------------------------------------------------------------===//
  
  #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
  #include "clang/AST/RecursiveASTVisitor.h"
  #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
  #include "clang/StaticAnalyzer/Core/Checker.h"
  #include "clang/StaticAnalyzer/Core/CheckerManager.h"
  #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
  
  using namespace clang;
  using namespace ento;
  
  namespace {
  class CastToStructVisitor : public RecursiveASTVisitor<CastToStructVisitor> {
    BugReporter &BR;
    const CheckerBase *Checker;
    AnalysisDeclContext *AC;
  
  public:
    explicit CastToStructVisitor(BugReporter &B, const CheckerBase *Checker,
                                 AnalysisDeclContext *A)
        : BR(B), Checker(Checker), AC(A) {}
    bool VisitCastExpr(const CastExpr *CE);
  };
  }
  
  bool CastToStructVisitor::VisitCastExpr(const CastExpr *CE) {
    const Expr *E = CE->getSubExpr();
    ASTContext &Ctx = AC->getASTContext();
    QualType OrigTy = Ctx.getCanonicalType(E->getType());
    QualType ToTy = Ctx.getCanonicalType(CE->getType());
  
    const PointerType *OrigPTy = dyn_cast<PointerType>(OrigTy.getTypePtr());
    const PointerType *ToPTy = dyn_cast<PointerType>(ToTy.getTypePtr());
  
    if (!ToPTy || !OrigPTy)
      return true;
  
    QualType OrigPointeeTy = OrigPTy->getPointeeType();
    QualType ToPointeeTy = ToPTy->getPointeeType();
  
    if (!ToPointeeTy->isStructureOrClassType())
      return true;
  
    // We allow cast from void*.
    if (OrigPointeeTy->isVoidType())
      return true;
  
    // Now the cast-to-type is struct pointer, the original type is not void*.
    if (!OrigPointeeTy->isRecordType()) {
      SourceRange Sr[1] = {CE->getSourceRange()};
      PathDiagnosticLocation Loc(CE, BR.getSourceManager(), AC);
      BR.EmitBasicReport(
          AC->getDecl(), Checker, "Cast from non-struct type to struct type",
          categories::LogicError, "Casting a non-structure type to a structure "
                                  "type and accessing a field can lead to memory "
                                  "access errors or data corruption.",
          Loc, Sr);
    } else {
      // Don't warn when size of data is unknown.
      const auto *U = dyn_cast<UnaryOperator>(E);
      if (!U || U->getOpcode() != UO_AddrOf)
        return true;
  
      // Don't warn for references
      const ValueDecl *VD = nullptr;
      if (const auto *SE = dyn_cast<DeclRefExpr>(U->getSubExpr()))
        VD = SE->getDecl();
      else if (const auto *SE = dyn_cast<MemberExpr>(U->getSubExpr()))
        VD = SE->getMemberDecl();
      if (!VD || VD->getType()->isReferenceType())
        return true;
  
      if (ToPointeeTy->isIncompleteType() ||
          OrigPointeeTy->isIncompleteType())
        return true;
  
      // Warn when there is widening cast.
      unsigned ToWidth = Ctx.getTypeInfo(ToPointeeTy).Width;
      unsigned OrigWidth = Ctx.getTypeInfo(OrigPointeeTy).Width;
      if (ToWidth <= OrigWidth)
        return true;
  
      PathDiagnosticLocation Loc(CE, BR.getSourceManager(), AC);
      BR.EmitBasicReport(AC->getDecl(), Checker, "Widening cast to struct type",
                         categories::LogicError,
                         "Casting data to a larger structure type and accessing "
                         "a field can lead to memory access errors or data "
                         "corruption.",
                         Loc, CE->getSourceRange());
    }
  
    return true;
  }
  
  namespace {
  class CastToStructChecker : public Checker<check::ASTCodeBody> {
  public:
    void checkASTCodeBody(const Decl *D, AnalysisManager &Mgr,
                          BugReporter &BR) const {
      CastToStructVisitor Visitor(BR, this, Mgr.getAnalysisDeclContext(D));
      Visitor.TraverseDecl(const_cast<Decl *>(D));
    }
  };
  } // end anonymous namespace
  
  void ento::registerCastToStructChecker(CheckerManager &mgr) {
    mgr.registerChecker<CastToStructChecker>();
  }
  
  bool ento::shouldRegisterCastToStructChecker(const LangOptions &LO) {
    return true;
  }
  