1//== ArrayBoundChecker.cpp ------------------------------*- C++ -*--==//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file defines ArrayBoundChecker, which is a path-sensitive check
11// which looks for an out-of-bound array element access.
12//
13//===----------------------------------------------------------------------===//
14
15#include "ClangSACheckers.h"
16#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
17#include "clang/StaticAnalyzer/Core/Checker.h"
18#include "clang/StaticAnalyzer/Core/CheckerManager.h"
19#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.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 NumElements
59    = C.getStoreManager().getSizeInElements(state, ER->getSuperRegion(),
60                                            ER->getValueType());
61
62  ProgramStateRef StInBound = state->assumeInBound(Idx, NumElements, true);
63  ProgramStateRef StOutBound = state->assumeInBound(Idx, NumElements, false);
64  if (StOutBound && !StInBound) {
65    ExplodedNode *N = C.generateSink(StOutBound);
66    if (!N)
67      return;
68
69    if (!BT)
70      BT.reset(new BuiltinBug(
71          this, "Out-of-bound array access",
72          "Access out-of-bound array element (buffer overflow)"));
73
74    // FIXME: It would be nice to eventually make this diagnostic more clear,
75    // e.g., by referencing the original declaration or by saying *why* this
76    // reference is outside the range.
77
78    // Generate a report for this bug.
79    BugReport *report =
80      new BugReport(*BT, BT->getDescription(), N);
81
82    report->addRange(LoadS->getSourceRange());
83    C.emitReport(report);
84    return;
85  }
86
87  // Array bound check succeeded.  From this point forward the array bound
88  // should always succeed.
89  C.addTransition(StInBound);
90}
91
92void ento::registerArrayBoundChecker(CheckerManager &mgr) {
93  mgr.registerChecker<ArrayBoundChecker>();
94}
95