ObjCContainersChecker.cpp revision 5251abea41b446c26e3239c8dd6c7edea6fc335d 
1//== ObjCContainersChecker.cpp - Path sensitive checker for CFArray *- 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// Performs path sensitive checks of Core Foundation static containers like
11// CFArray.
12// 1) Check for buffer overflows:
13//      In CFArrayGetArrayAtIndex( myArray, index), if the index is outside the
14//      index space of theArray (0 to N-1 inclusive (where N is the count of
15//      theArray), the behavior is undefined.
16//
17//===----------------------------------------------------------------------===//
18
19#include "ClangSACheckers.h"
20#include "clang/AST/ParentMap.h"
21#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
22#include "clang/StaticAnalyzer/Core/Checker.h"
23#include "clang/StaticAnalyzer/Core/CheckerManager.h"
24#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
25#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramStateTrait.h"
26
27using namespace clang;
28using namespace ento;
29
30namespace {
31class ObjCContainersChecker : public Checker< check::PreStmt<CallExpr>,
32                                             check::PostStmt<CallExpr> > {
33  mutable OwningPtr<BugType> BT;
34  inline void initBugType() const {
35    if (!BT)
36      BT.reset(new BugType("CFArray API",
37                           categories::CoreFoundationObjectiveC));
38  }
39
40  inline SymbolRef getArraySym(const Expr *E, CheckerContext &C) const {
41    SVal ArrayRef = C.getState()->getSVal(E, C.getLocationContext());
42    SymbolRef ArraySym = ArrayRef.getAsSymbol();
43    return ArraySym;
44  }
45
46  void addSizeInfo(const Expr *Array, const Expr *Size,
47                   CheckerContext &C) const;
48
49public:
50  /// A tag to id this checker.
51  static void *getTag() { static int Tag; return &Tag; }
52
53  void checkPostStmt(const CallExpr *CE, CheckerContext &C) const;
54  void checkPreStmt(const CallExpr *CE, CheckerContext &C) const;
55};
56} // end anonymous namespace
57
58// ProgramState trait - a map from array symbol to its state.
59REGISTER_MAP_WITH_PROGRAMSTATE(ArraySizeMap, SymbolRef, DefinedSVal)
60
61void ObjCContainersChecker::addSizeInfo(const Expr *Array, const Expr *Size,
62                                        CheckerContext &C) const {
63  ProgramStateRef State = C.getState();
64  SVal SizeV = State->getSVal(Size, C.getLocationContext());
65  // Undefined is reported by another checker.
66  if (SizeV.isUnknownOrUndef())
67    return;
68
69  // Get the ArrayRef symbol.
70  SVal ArrayRef = State->getSVal(Array, C.getLocationContext());
71  SymbolRef ArraySym = ArrayRef.getAsSymbol();
72  if (!ArraySym)
73    return;
74
75  C.addTransition(
76      State->set<ArraySizeMap>(ArraySym, SizeV.castAs<DefinedSVal>()));
77  return;
78}
79
80void ObjCContainersChecker::checkPostStmt(const CallExpr *CE,
81                                          CheckerContext &C) const {
82  StringRef Name = C.getCalleeName(CE);
83  if (Name.empty() || CE->getNumArgs() < 1)
84    return;
85
86  // Add array size information to the state.
87  if (Name.equals("CFArrayCreate")) {
88    if (CE->getNumArgs() < 3)
89      return;
90    // Note, we can visit the Create method in the post-visit because
91    // the CFIndex parameter is passed in by value and will not be invalidated
92    // by the call.
93    addSizeInfo(CE, CE->getArg(2), C);
94    return;
95  }
96
97  if (Name.equals("CFArrayGetCount")) {
98    addSizeInfo(CE->getArg(0), CE, C);
99    return;
100  }
101}
102
103void ObjCContainersChecker::checkPreStmt(const CallExpr *CE,
104                                         CheckerContext &C) const {
105  StringRef Name = C.getCalleeName(CE);
106  if (Name.empty() || CE->getNumArgs() < 2)
107    return;
108
109  // Check the array access.
110  if (Name.equals("CFArrayGetValueAtIndex")) {
111    ProgramStateRef State = C.getState();
112    // Retrieve the size.
113    // Find out if we saw this array symbol before and have information about it.
114    const Expr *ArrayExpr = CE->getArg(0);
115    SymbolRef ArraySym = getArraySym(ArrayExpr, C);
116    if (!ArraySym)
117      return;
118
119    const DefinedSVal *Size = State->get<ArraySizeMap>(ArraySym);
120
121    if (!Size)
122      return;
123
124    // Get the index.
125    const Expr *IdxExpr = CE->getArg(1);
126    SVal IdxVal = State->getSVal(IdxExpr, C.getLocationContext());
127    if (IdxVal.isUnknownOrUndef())
128      return;
129    DefinedSVal Idx = IdxVal.castAs<DefinedSVal>();
130
131    // Now, check if 'Idx in [0, Size-1]'.
132    const QualType T = IdxExpr->getType();
133    ProgramStateRef StInBound = State->assumeInBound(Idx, *Size, true, T);
134    ProgramStateRef StOutBound = State->assumeInBound(Idx, *Size, false, T);
135    if (StOutBound && !StInBound) {
136      ExplodedNode *N = C.generateSink(StOutBound);
137      if (!N)
138        return;
139      initBugType();
140      BugReport *R = new BugReport(*BT, "Index is out of bounds", N);
141      R->addRange(IdxExpr->getSourceRange());
142      C.emitReport(R);
143      return;
144    }
145  }
146}
147
148/// Register checker.
149void ento::registerObjCContainersChecker(CheckerManager &mgr) {
150  mgr.registerChecker<ObjCContainersChecker>();
151}
152