PointerSubChecker.cpp revision 695fb502825a53ccd178ec1c85c77929d88acb71 
1//=== PointerSubChecker.cpp - Pointer subtraction checker ------*- 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 files defines PointerSubChecker, a builtin checker that checks for
11// pointer subtractions on two pointers pointing to different memory chunks.
12// This check corresponds to CWE-469.
13//
14//===----------------------------------------------------------------------===//
15
16#include "ClangSACheckers.h"
17#include "clang/StaticAnalyzer/Core/CheckerManager.h"
18#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
19#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerVisitor.h"
20
21using namespace clang;
22using namespace ento;
23
24namespace {
25class PointerSubChecker
26  : public CheckerVisitor<PointerSubChecker> {
27  BuiltinBug *BT;
28public:
29  PointerSubChecker() : BT(0) {}
30  static void *getTag();
31  void PreVisitBinaryOperator(CheckerContext &C, const BinaryOperator *B);
32};
33}
34
35void *PointerSubChecker::getTag() {
36  static int x;
37  return &x;
38}
39
40void PointerSubChecker::PreVisitBinaryOperator(CheckerContext &C,
41                                               const BinaryOperator *B) {
42  // When doing pointer subtraction, if the two pointers do not point to the
43  // same memory chunk, emit a warning.
44  if (B->getOpcode() != BO_Sub)
45    return;
46
47  const GRState *state = C.getState();
48  SVal LV = state->getSVal(B->getLHS());
49  SVal RV = state->getSVal(B->getRHS());
50
51  const MemRegion *LR = LV.getAsRegion();
52  const MemRegion *RR = RV.getAsRegion();
53
54  if (!(LR && RR))
55    return;
56
57  const MemRegion *BaseLR = LR->getBaseRegion();
58  const MemRegion *BaseRR = RR->getBaseRegion();
59
60  if (BaseLR == BaseRR)
61    return;
62
63  // Allow arithmetic on different symbolic regions.
64  if (isa<SymbolicRegion>(BaseLR) || isa<SymbolicRegion>(BaseRR))
65    return;
66
67  if (ExplodedNode *N = C.generateNode()) {
68    if (!BT)
69      BT = new BuiltinBug("Pointer subtraction",
70                          "Subtraction of two pointers that do not point to "
71                          "the same memory chunk may cause incorrect result.");
72    RangedBugReport *R = new RangedBugReport(*BT, BT->getDescription(), N);
73    R->addRange(B->getSourceRange());
74    C.EmitReport(R);
75  }
76}
77
78static void RegisterPointerSubChecker(ExprEngine &Eng) {
79  Eng.registerCheck(new PointerSubChecker());
80}
81
82void ento::registerPointerSubChecker(CheckerManager &mgr) {
83  mgr.addCheckerRegisterFunction(RegisterPointerSubChecker);
84}
85