//== ArrayBoundChecker.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 file defines ArrayBoundChecker, which is a path-sensitive check

// which looks for an out-of-bound array element access.

//

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

#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"

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

using namespace clang;

using namespace ento;

namespace {

class ArrayBoundChecker :

    public Checker<check::Location> {

  mutable std::unique_ptr<BugType> BT;

public:

  void checkLocation(SVal l, bool isLoad, const Stmt* S,

                     CheckerContext &C) const;

};

}

void ArrayBoundChecker::checkLocation(SVal l, bool isLoad, const Stmt* LoadS,

                                      CheckerContext &C) const {

  // Check for out of bound array element access.

  const MemRegion *R = l.getAsRegion();

  if (!R)

    return;

  const ElementRegion *ER = dyn_cast<ElementRegion>(R);

  if (!ER)

    return;

  // Get the index of the accessed element.

  DefinedOrUnknownSVal Idx = ER->getIndex().castAs<DefinedOrUnknownSVal>();

  // Zero index is always in bound, this also passes ElementRegions created for

  // pointer casts.

  if (Idx.isZeroConstant())

    return;

  ProgramStateRef state = C.getState();

  // Get the size of the array.

  DefinedOrUnknownSVal ElementCount = getDynamicElementCount(

      state, ER->getSuperRegion(), C.getSValBuilder(), ER->getValueType());

  ProgramStateRef StInBound, StOutBound;

  std::tie(StInBound, StOutBound) = state->assumeInBoundDual(Idx, ElementCount);

  if (StOutBound && 
!StInBound83
) {

    ExplodedNode *N = C.generateErrorNode(StOutBound);

    if (!N)

      return;

    if (!BT)

      BT.reset(new BugType(this, "Out-of-bound array access"));

    // FIXME: It would be nice to eventually make this diagnostic more clear,

    // e.g., by referencing the original declaration or by saying *why* this

    // reference is outside the range.

    // Generate a report for this bug.

    auto report = std::make_unique<PathSensitiveBugReport>(

        *BT, "Access out-of-bound array element (buffer overflow)", N);

    report->addRange(LoadS->getSourceRange());

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

    return;

  }

  // Array bound check succeeded.  From this point forward the array bound

  // should always succeed.

  C.addTransition(StInBound);

}

void ento::registerArrayBoundChecker(CheckerManager &mgr) {

  mgr.registerChecker<ArrayBoundChecker>();

}

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

  return true;

}