ObjCContainersChecker.cpp revision 166d502d5367ceacd1313a33cac43b1048b8524d 
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/StaticAnalyzer/Core/Checker.h"
21#include "clang/StaticAnalyzer/Core/CheckerManager.h"
22#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
23#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramStateTrait.h"
24#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
25#include "clang/AST/ParentMap.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(State->set<ArraySizeMap>(ArraySym, cast<DefinedSVal>(SizeV)));
76  return;
77}
78
79void ObjCContainersChecker::checkPostStmt(const CallExpr *CE,
80                                          CheckerContext &C) const {
81  StringRef Name = C.getCalleeName(CE);
82  if (Name.empty() || CE->getNumArgs() < 1)
83    return;
84
85  // Add array size information to the state.
86  if (Name.equals("CFArrayCreate")) {
87    if (CE->getNumArgs() < 3)
88      return;
89    // Note, we can visit the Create method in the post-visit because
90    // the CFIndex parameter is passed in by value and will not be invalidated
91    // by the call.
92    addSizeInfo(CE, CE->getArg(2), C);
93    return;
94  }
95
96  if (Name.equals("CFArrayGetCount")) {
97    addSizeInfo(CE->getArg(0), CE, C);
98    return;
99  }
100}
101
102void ObjCContainersChecker::checkPreStmt(const CallExpr *CE,
103                                         CheckerContext &C) const {
104  StringRef Name = C.getCalleeName(CE);
105  if (Name.empty() || CE->getNumArgs() < 2)
106    return;
107
108  // Check the array access.
109  if (Name.equals("CFArrayGetValueAtIndex")) {
110    ProgramStateRef State = C.getState();
111    // Retrieve the size.
112    // Find out if we saw this array symbol before and have information about it.
113    const Expr *ArrayExpr = CE->getArg(0);
114    SymbolRef ArraySym = getArraySym(ArrayExpr, C);
115    if (!ArraySym)
116      return;
117
118    const DefinedSVal *Size = State->get<ArraySizeMap>(ArraySym);
119
120    if (!Size)
121      return;
122
123    // Get the index.
124    const Expr *IdxExpr = CE->getArg(1);
125    SVal IdxVal = State->getSVal(IdxExpr, C.getLocationContext());
126    if (IdxVal.isUnknownOrUndef())
127      return;
128    DefinedSVal Idx = cast<DefinedSVal>(IdxVal);
129
130    // Now, check if 'Idx in [0, Size-1]'.
131    const QualType T = IdxExpr->getType();
132    ProgramStateRef StInBound = State->assumeInBound(Idx, *Size, true, T);
133    ProgramStateRef StOutBound = State->assumeInBound(Idx, *Size, false, T);
134    if (StOutBound && !StInBound) {
135      ExplodedNode *N = C.generateSink(StOutBound);
136      if (!N)
137        return;
138      initBugType();
139      BugReport *R = new BugReport(*BT, "Index is out of bounds", N);
140      R->addRange(IdxExpr->getSourceRange());
141      C.emitReport(R);
142      return;
143    }
144  }
145}
146
147/// Register checker.
148void ento::registerObjCContainersChecker(CheckerManager &mgr) {
149  mgr.registerChecker<ObjCContainersChecker>();
150}
151