ObjCContainersChecker.cpp revision 785950e59424dca7ce0081bebf13c0acd2c4fff6 
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 it's state.
59typedef llvm::ImmutableMap<SymbolRef, DefinedSVal> ArraySizeM;
60
61namespace { struct ArraySizeMap {}; }
62namespace clang { namespace ento {
63template<> struct ProgramStateTrait<ArraySizeMap>
64    :  public ProgramStatePartialTrait<ArraySizeM > {
65  static void *GDMIndex() { return ObjCContainersChecker::getTag(); }
66};
67}}
68
69void ObjCContainersChecker::addSizeInfo(const Expr *Array, const Expr *Size,
70                                        CheckerContext &C) const {
71  ProgramStateRef State = C.getState();
72  SVal SizeV = State->getSVal(Size, C.getLocationContext());
73  // Undefined is reported by another checker.
74  if (SizeV.isUnknownOrUndef())
75    return;
76
77  // Get the ArrayRef symbol.
78  SVal ArrayRef = State->getSVal(Array, C.getLocationContext());
79  SymbolRef ArraySym = ArrayRef.getAsSymbol();
80  if (!ArraySym)
81    return;
82
83  C.addTransition(State->set<ArraySizeMap>(ArraySym, cast<DefinedSVal>(SizeV)));
84  return;
85}
86
87void ObjCContainersChecker::checkPostStmt(const CallExpr *CE,
88                                          CheckerContext &C) const {
89  StringRef Name = C.getCalleeName(CE);
90  if (Name.empty() || CE->getNumArgs() < 1)
91    return;
92
93  // Add array size information to the state.
94  if (Name.equals("CFArrayCreate")) {
95    if (CE->getNumArgs() < 3)
96      return;
97    // Note, we can visit the Create method in the post-visit because
98    // the CFIndex parameter is passed in by value and will not be invalidated
99    // by the call.
100    addSizeInfo(CE, CE->getArg(2), C);
101    return;
102  }
103
104  if (Name.equals("CFArrayGetCount")) {
105    addSizeInfo(CE->getArg(0), CE, C);
106    return;
107  }
108}
109
110void ObjCContainersChecker::checkPreStmt(const CallExpr *CE,
111                                         CheckerContext &C) const {
112  StringRef Name = C.getCalleeName(CE);
113  if (Name.empty() || CE->getNumArgs() < 2)
114    return;
115
116  // Check the array access.
117  if (Name.equals("CFArrayGetValueAtIndex")) {
118    ProgramStateRef State = C.getState();
119    // Retrieve the size.
120    // Find out if we saw this array symbol before and have information about it.
121    const Expr *ArrayExpr = CE->getArg(0);
122    SymbolRef ArraySym = getArraySym(ArrayExpr, C);
123    if (!ArraySym)
124      return;
125
126    const DefinedSVal *Size = State->get<ArraySizeMap>(ArraySym);
127
128    if (!Size)
129      return;
130
131    // Get the index.
132    const Expr *IdxExpr = CE->getArg(1);
133    SVal IdxVal = State->getSVal(IdxExpr, C.getLocationContext());
134    if (IdxVal.isUnknownOrUndef())
135      return;
136    DefinedSVal Idx = cast<DefinedSVal>(IdxVal);
137
138    // Now, check if 'Idx in [0, Size-1]'.
139    const QualType T = IdxExpr->getType();
140    ProgramStateRef StInBound = State->assumeInBound(Idx, *Size, true, T);
141    ProgramStateRef StOutBound = State->assumeInBound(Idx, *Size, false, T);
142    if (StOutBound && !StInBound) {
143      ExplodedNode *N = C.generateSink(StOutBound);
144      if (!N)
145        return;
146      initBugType();
147      BugReport *R = new BugReport(*BT, "Index is out of bounds", N);
148      R->addRange(IdxExpr->getSourceRange());
149      C.emitReport(R);
150      return;
151    }
152  }
153}
154
155/// Register checker.
156void ento::registerObjCContainersChecker(CheckerManager &mgr) {
157  mgr.registerChecker<ObjCContainersChecker>();
158}
159