PointerSubChecker.cpp revision 0bd6b110e908892d4b5c8671a9f435a1d72ad16a 
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  const ProgramState *state = C.getState();
43  SVal LV = state->getSVal(B->getLHS());
44  SVal RV = state->getSVal(B->getRHS());
45
46  const MemRegion *LR = LV.getAsRegion();
47  const MemRegion *RR = RV.getAsRegion();
48
49  if (!(LR && RR))
50    return;
51
52  const MemRegion *BaseLR = LR->getBaseRegion();
53  const MemRegion *BaseRR = RR->getBaseRegion();
54
55  if (BaseLR == BaseRR)
56    return;
57
58  // Allow arithmetic on different symbolic regions.
59  if (isa<SymbolicRegion>(BaseLR) || isa<SymbolicRegion>(BaseRR))
60    return;
61
62  if (ExplodedNode *N = C.addTransition()) {
63    if (!BT)
64      BT.reset(new BuiltinBug("Pointer subtraction",
65                          "Subtraction of two pointers that do not point to "
66                          "the same memory chunk may cause incorrect result."));
67    BugReport *R = new BugReport(*BT, BT->getDescription(), N);
68    R->addRange(B->getSourceRange());
69    C.EmitReport(R);
70  }
71}
72
73void ento::registerPointerSubChecker(CheckerManager &mgr) {
74  mgr.registerChecker<PointerSubChecker>();
75}
76