//=== CastSizeChecker.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

//

//===----------------------------------------------------------------------===//

//

// CastSizeChecker checks when casting a malloc'ed symbolic region to type T,

// whether the size of the symbolic region is a multiple of the size of T.

//

//===----------------------------------------------------------------------===//

#include "clang/AST/CharUnits.h"

#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.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"

#include "clang/StaticAnalyzer/Core/PathSensitive/DynamicExtent.h"

using namespace clang;

using namespace ento;

namespace {

class CastSizeChecker : public Checker< check::PreStmt<CastExpr> > {

  mutable std::unique_ptr<BugType> BT;

public:

  void checkPreStmt(const CastExpr *CE, CheckerContext &C) const;

};

}

/// Check if we are casting to a struct with a flexible array at the end.

/// \code

/// struct foo {

///   size_t len;

///   struct bar data[];

/// };

/// \endcode

/// or

/// \code

/// struct foo {

///   size_t len;

///   struct bar data[0];

/// }

/// \endcode

/// In these cases it is also valid to allocate size of struct foo + a multiple

/// of struct bar.

static bool evenFlexibleArraySize(ASTContext &Ctx, CharUnits RegionSize,

                                  CharUnits TypeSize, QualType ToPointeeTy) {

  const RecordType *RT = ToPointeeTy->getAs<RecordType>();

  if (!RT)

    return false;

  const RecordDecl *RD = RT->getDecl();

  RecordDecl::field_iterator Iter(RD->field_begin());

  RecordDecl::field_iterator End(RD->field_end());

  const FieldDecl *Last = nullptr;

  for (; Iter != End; 
++Iter30
)

    Last = *Iter;

  assert(Last && "empty structs should already be handled");

  const Type *ElemType = Last->getType()->getArrayElementTypeNoTypeQual();

  CharUnits FlexSize;

  if (const ConstantArrayType *ArrayTy =

        Ctx.getAsConstantArrayType(Last->getType())) {

    FlexSize = Ctx.getTypeSizeInChars(ElemType);

    if (ArrayTy->getSize() == 1 && 
TypeSize > FlexSize5
)

      TypeSize -= FlexSize;

    else if (ArrayTy->getSize() != 0)

      return false;

  } else 
if (4
RD->hasFlexibleArrayMember()4
) {

    FlexSize = Ctx.getTypeSizeInChars(ElemType);

  } else {

    return false;

  }

  if (FlexSize.isZero())

    return false;

  CharUnits Left = RegionSize - TypeSize;

  if (Left.isNegative())

    return false;

  return Left % FlexSize == 0;

}

void CastSizeChecker::checkPreStmt(const CastExpr *CE,CheckerContext &C) const {

  const Expr *E = CE->getSubExpr();

  ASTContext &Ctx = C.getASTContext();

  QualType ToTy = Ctx.getCanonicalType(CE->getType());

  const PointerType *ToPTy = dyn_cast<PointerType>(ToTy.getTypePtr());

  if (!ToPTy)

    return;

  QualType ToPointeeTy = ToPTy->getPointeeType();

  // Only perform the check if 'ToPointeeTy' is a complete type.

  if (ToPointeeTy->isIncompleteType())

    return;

  ProgramStateRef state = C.getState();

  const MemRegion *R = C.getSVal(E).getAsRegion();

  if (!R)

    return;

  const SymbolicRegion *SR = dyn_cast<SymbolicRegion>(R);

  if (!SR)

    return;

  SValBuilder &svalBuilder = C.getSValBuilder();

  DefinedOrUnknownSVal Size = getDynamicExtent(state, SR, svalBuilder);

  const llvm::APSInt *SizeInt = svalBuilder.getKnownValue(state, Size);

  if (!SizeInt)

    return;

  CharUnits regionSize = CharUnits::fromQuantity(SizeInt->getZExtValue());

  CharUnits typeSize = C.getASTContext().getTypeSizeInChars(ToPointeeTy);

  // Ignore void, and a few other un-sizeable types.

  if (typeSize.isZero())

    return;

  if (regionSize % typeSize == 0)

    return;

  if (evenFlexibleArraySize(Ctx, regionSize, typeSize, ToPointeeTy))

    return;

  if (ExplodedNode *errorNode = C.generateErrorNode()) {

    if (!BT)

      BT.reset(new BugType(this, "Cast region with wrong size."));

    constexpr llvm::StringLiteral Msg =

        "Cast a region whose size is not a multiple of the destination type "

        "size.";

    auto R = std::make_unique<PathSensitiveBugReport>(*BT, Msg, errorNode);

    R->addRange(CE->getSourceRange());

    C.emitReport(std::move(R));

  }

}

void ento::registerCastSizeChecker(CheckerManager &mgr) {

  mgr.registerChecker<CastSizeChecker>();

}

bool ento::shouldRegisterCastSizeChecker(const CheckerManager &mgr) {

  // PR31226: C++ is more complicated than what this checker currently supports.

  // There are derived-to-base casts, there are different rules for 0-size

  // structures, no flexible arrays, etc.

  // FIXME: Disabled on C++ for now.

  const LangOptions &LO = mgr.getLangOpts();

  return !LO.CPlusPlus;

}