1//== ArrayBoundChecker.cpp ------------------------------*- C++ -*--==//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file defines ArrayBoundChecker, which is a path-sensitive check
10// which looks for an out-of-bound array element access.
11//
12//===----------------------------------------------------------------------===//
13
14#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
15#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
16#include "clang/StaticAnalyzer/Core/Checker.h"
17#include "clang/StaticAnalyzer/Core/CheckerManager.h"
18#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
19#include "clang/StaticAnalyzer/Core/PathSensitive/DynamicExtent.h"
20#include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
21
22using namespace clang;
23using namespace ento;
24
25namespace {
26class ArrayBoundChecker :
27    public Checker<check::Location> {
28  mutable std::unique_ptr<BuiltinBug> BT;
29
30public:
31  void checkLocation(SVal l, bool isLoad, const Stmt* S,
32                     CheckerContext &C) const;
33};
34}
35
36void ArrayBoundChecker::checkLocation(SVal l, bool isLoad, const Stmt* LoadS,
37                                      CheckerContext &C) const {
38  // Check for out of bound array element access.
39  const MemRegion *R = l.getAsRegion();
40  if (!R)
41    return;
42
43  const ElementRegion *ER = dyn_cast<ElementRegion>(R);
44  if (!ER)
45    return;
46
47  // Get the index of the accessed element.
48  DefinedOrUnknownSVal Idx = ER->getIndex().castAs<DefinedOrUnknownSVal>();
49
50  // Zero index is always in bound, this also passes ElementRegions created for
51  // pointer casts.
52  if (Idx.isZeroConstant())
53    return;
54
55  ProgramStateRef state = C.getState();
56
57  // Get the size of the array.
58  DefinedOrUnknownSVal ElementCount = getDynamicElementCount(
59      state, ER->getSuperRegion(), C.getSValBuilder(), ER->getValueType());
60
61  ProgramStateRef StInBound, StOutBound;
62  std::tie(StInBound, StOutBound) = state->assumeInBoundDual(Idx, ElementCount);
63  if (StOutBound && !StInBound) {
64    ExplodedNode *N = C.generateErrorNode(StOutBound);
65    if (!N)
66      return;
67
68    if (!BT)
69      BT.reset(new BuiltinBug(
70          this, "Out-of-bound array access",
71          "Access out-of-bound array element (buffer overflow)"));
72
73    // FIXME: It would be nice to eventually make this diagnostic more clear,
74    // e.g., by referencing the original declaration or by saying *why* this
75    // reference is outside the range.
76
77    // Generate a report for this bug.
78    auto report =
79        std::make_unique<PathSensitiveBugReport>(*BT, BT->getDescription(), N);
80
81    report->addRange(LoadS->getSourceRange());
82    C.emitReport(std::move(report));
83    return;
84  }
85
86  // Array bound check succeeded.  From this point forward the array bound
87  // should always succeed.
88  C.addTransition(StInBound);
89}
90
91void ento::registerArrayBoundChecker(CheckerManager &mgr) {
92  mgr.registerChecker<ArrayBoundChecker>();
93}
94
95bool ento::shouldRegisterArrayBoundChecker(const CheckerManager &mgr) {
96  return true;
97}
98