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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> > {
mutable std::unique_ptr<BuiltinBug> 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; ++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->getSize() != 0)
return false;
} else if (RD->hasFlexibleArrayMember()) {
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 BuiltinBug(this, "Cast region with wrong size.",
"Cast a region whose size is not a multiple"
" of the destination type size."));
auto R = std::make_unique<PathSensitiveBugReport>(*BT, BT->getDescription(),
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;
}
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