PointerSubChecker.cpp revision 8bef8238181a30e52dea380789a7e2d760eac532 
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/Checker.h"
18#include "clang/StaticAnalyzer/Core/CheckerManager.h"
19#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
20#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
21
22using namespace clang;
23using namespace ento;
24
25namespace {
26class PointerSubChecker
27  : public Checker< check::PreStmt<BinaryOperator> > {
28  mutable llvm::OwningPtr<BuiltinBug> BT;
29
30public:
31  void checkPreStmt(const BinaryOperator *B, CheckerContext &C) const;
32};
33}
34
35void PointerSubChecker::checkPreStmt(const BinaryOperator *B,
36                                     CheckerContext &C) const {
37  // When doing pointer subtraction, if the two pointers do not point to the
38  // same memory chunk, emit a warning.
39  if (B->getOpcode() != BO_Sub)
40    return;
41
42  ProgramStateRef state = C.getState();
43  const LocationContext *LCtx = C.getLocationContext();
44  SVal LV = state->getSVal(B->getLHS(), LCtx);
45  SVal RV = state->getSVal(B->getRHS(), LCtx);
46
47  const MemRegion *LR = LV.getAsRegion();
48  const MemRegion *RR = RV.getAsRegion();
49
50  if (!(LR && RR))
51    return;
52
53  const MemRegion *BaseLR = LR->getBaseRegion();
54  const MemRegion *BaseRR = RR->getBaseRegion();
55
56  if (BaseLR == BaseRR)
57    return;
58
59  // Allow arithmetic on different symbolic regions.
60  if (isa<SymbolicRegion>(BaseLR) || isa<SymbolicRegion>(BaseRR))
61    return;
62
63  if (ExplodedNode *N = C.addTransition()) {
64    if (!BT)
65      BT.reset(new BuiltinBug("Pointer subtraction",
66                          "Subtraction of two pointers that do not point to "
67                          "the same memory chunk may cause incorrect result."));
68    BugReport *R = new BugReport(*BT, BT->getDescription(), N);
69    R->addRange(B->getSourceRange());
70    C.EmitReport(R);
71  }
72}
73
74void ento::registerPointerSubChecker(CheckerManager &mgr) {
75  mgr.registerChecker<PointerSubChecker>();
76}
77