ObjCContainersChecker.cpp revision af5f550de34525b27f0ff31dafce792caf8158b6 
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/PathSensitive/ObjCMessage.h"
25#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
26#include "clang/AST/ParentMap.h"
27
28using namespace clang;
29using namespace ento;
30
31namespace {
32class ObjCContainersChecker : public Checker< check::PreStmt<CallExpr>,
33                                             check::PostStmt<CallExpr> > {
34  mutable llvm::OwningPtr<BugType> BT;
35  inline void initBugType() const {
36    if (!BT)
37      BT.reset(new BugType("CFArray API", "Core Foundation/Objective-C API"));
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    assert(ArraySym);
44    return ArraySym;
45  }
46
47  void addSizeInfo(const Expr *Array, const Expr *Size,
48                   CheckerContext &C) const;
49
50public:
51  /// A tag to id this checker.
52  static void *getTag() { static int Tag; return &Tag; }
53
54  void checkPostStmt(const CallExpr *CE, CheckerContext &C) const;
55  void checkPreStmt(const CallExpr *CE, CheckerContext &C) const;
56};
57} // end anonymous namespace
58
59// Array state stores the array size on creation (allocation).
60// Size might be an unsigned or a symbol.
61struct ArraySize {
62  SVal NLSize;
63  ArraySize(SVal s) : NLSize(s) {}
64  void Profile(llvm::FoldingSetNodeID &ID) const {
65    NLSize.Profile(ID);
66  }
67};
68
69// ProgramState trait - a map from array symbol to it's state.
70typedef llvm::ImmutableMap<SymbolRef, SVal> ArraySizeM;
71
72namespace { struct ArraySizeMap {}; }
73namespace clang { namespace ento {
74template<> struct ProgramStateTrait<ArraySizeMap>
75    :  public ProgramStatePartialTrait<ArraySizeM > {
76  static void *GDMIndex() { return ObjCContainersChecker::getTag(); }
77};
78}}
79
80void ObjCContainersChecker::addSizeInfo(const Expr *Array, const Expr *Size,
81                                        CheckerContext &C) const {
82  const ProgramState *State = C.getState();
83  SVal SizeV = State->getSVal(Size, C.getLocationContext());
84  // Undefined is reported by another checker.
85  if (SizeV.isUnknownOrUndef())
86    return;
87
88  // Get the ArrayRef symbol.
89  SVal ArrayRef = State->getSVal(Array, C.getLocationContext());
90  SymbolRef ArraySym = ArrayRef.getAsSymbol();
91  if (!ArraySym)
92    return;
93
94  C.addTransition(State->set<ArraySizeMap>(ArraySym, SizeV));
95  return;
96}
97
98void ObjCContainersChecker::checkPostStmt(const CallExpr *CE,
99                                          CheckerContext &C) const {
100  StringRef Name = C.getCalleeName(CE);
101  if (Name.empty())
102    return;
103
104  // Add array size information to the state.
105  if (Name.equals("CFArrayCreate")) {
106    // Note, we can visit the Create method in the post-visit because
107    // the CFIndex parameter is passed in by value and will not be invalidated
108    // by the call.
109    addSizeInfo(CE, CE->getArg(2), C);
110    return;
111  }
112
113  if (Name.equals("CFArrayGetCount")) {
114    addSizeInfo(CE->getArg(0), CE, C);
115    return;
116  }
117}
118
119void ObjCContainersChecker::checkPreStmt(const CallExpr *CE,
120                                         CheckerContext &C) const {
121  StringRef Name = C.getCalleeName(CE);
122  if (Name.empty())
123    return;
124
125  // Check the array access.
126  if (Name.equals("CFArrayGetValueAtIndex")) {
127    const ProgramState *State = C.getState();
128    // Retrieve the size.
129    // Find out if we saw this array symbol before and have information about it.
130    const Expr *ArrayExpr = CE->getArg(0);
131    const SVal *SizeVal = State->get<ArraySizeMap>(getArraySym(ArrayExpr, C));
132    if (!SizeVal)
133      return;
134    DefinedOrUnknownSVal Size = cast<DefinedOrUnknownSVal>(*SizeVal);
135
136    // Get the index.
137    const Expr *IdxExpr = CE->getArg(1);
138    SVal IdxVal = State->getSVal(IdxExpr, C.getLocationContext());
139    DefinedOrUnknownSVal Idx = cast<DefinedOrUnknownSVal>(IdxVal);
140
141    // Now, check if 'Idx in [0, Size-1]'.
142    const QualType T = IdxExpr->getType();
143    const ProgramState *StInBound = State->assumeInBound(Idx, Size, true, T);
144    const ProgramState *StOutBound = State->assumeInBound(Idx, Size, false, T);
145    if (StOutBound && !StInBound) {
146      ExplodedNode *N = C.generateSink(StOutBound);
147      if (!N)
148        return;
149      initBugType();
150      BugReport *R = new BugReport(*BT, "Index is out of bounds", N);
151      R->addRange(IdxExpr->getSourceRange());
152      C.EmitReport(R);
153      return;
154    }
155  }
156}
157
158/// Register checker.
159void ento::registerObjCContainersChecker(CheckerManager &mgr) {
160  mgr.registerChecker<ObjCContainersChecker>();
161}
162