CastSizeChecker.cpp

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//=== 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> > {
  const BugType BT{this, "Cast region with wrong size."};
 
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; ++Iter)
    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 > FlexSize)
      TypeSize -= FlexSize;
    else if (!ArrayTy->isZeroSize())
      return false;
  } else if (RD->