//=== PointerSubChecker.cpp - Pointer subtraction checker ------*- 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 PointerSubChecker, a builtin checker that checks for

// pointer subtractions on two pointers pointing to different memory chunks.

// This check corresponds to CWE-469.

//

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

#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 "llvm/ADT/StringRef.h"

using namespace clang;

using namespace ento;

namespace {

class PointerSubChecker

  : public Checker< check::PreStmt<BinaryOperator> > {

  mutable std::unique_ptr<BugType> BT;

public:

  void checkPreStmt(const BinaryOperator *B, CheckerContext &C) const;

};

}

void PointerSubChecker::checkPreStmt(const BinaryOperator *B,

                                     CheckerContext &C) const {

  // When doing pointer subtraction, if the two pointers do not point to the

  // same memory chunk, emit a warning.

  if (B->getOpcode() != BO_Sub)

    return;

  SVal LV = C.getSVal(B->getLHS());

  SVal RV = C.getSVal(B->getRHS());

  const MemRegion *LR = LV.getAsRegion();

  const MemRegion *RR = RV.getAsRegion();

  if (!(LR && 
RR68
))

    return;

  const MemRegion *BaseLR = LR->getBaseRegion();

  const MemRegion *BaseRR = RR->getBaseRegion();

  if (BaseLR == BaseRR)

    return;

  // Allow arithmetic on different symbolic regions.

  if (isa<SymbolicRegion>(BaseLR) || 
isa<SymbolicRegion>(BaseRR)2
)

    return;

  if (ExplodedNode *N = C.generateNonFatalErrorNode()) {

    if (!BT)

      BT.reset(new BugType(this, "Pointer subtraction"));

    constexpr llvm::StringLiteral Msg =

        "Subtraction of two pointers that do not point to the same memory "

        "chunk may cause incorrect result.";

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

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

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

  }

}

void ento::registerPointerSubChecker(CheckerManager &mgr) {

  mgr.registerChecker<PointerSubChecker>();

}

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

  return true;

}