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 "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.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 
27 using namespace clang;
28 using namespace ento;
29 
30 namespace {
31 class ObjCContainersChecker : public Checker< check::PreStmt<CallExpr>,
32                                              check::PostStmt<CallExpr>,
33                                              check::PointerEscape> {
34   mutable std::unique_ptr<BugType> BT;
35   inline void initBugType() const {
36     if (!BT)
37       BT.reset(new BugType(this, "CFArray API",
38                            categories::CoreFoundationObjectiveC));
39   }
40 
41   inline SymbolRef getArraySym(const Expr *E, CheckerContext &C) const {
42     SVal ArrayRef = C.getSVal(E);
43     SymbolRef ArraySym = ArrayRef.getAsSymbol();
44     return ArraySym;
45   }
46 
47   void addSizeInfo(const Expr *Array, const Expr *Size,
48                    CheckerContext &C) const;
49 
50 public:
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   ProgramStateRef checkPointerEscape(ProgramStateRef State,
57                                      const InvalidatedSymbols &Escaped,
58                                      const CallEvent *Call,
59                                      PointerEscapeKind Kind) const;
60 
61   void printState(raw_ostream &OS, ProgramStateRef State,
62                   const char *NL, const char *Sep) const;
63 };
64 } // end anonymous namespace
65 
66 // ProgramState trait - a map from array symbol to its state.
67 REGISTER_MAP_WITH_PROGRAMSTATE(ArraySizeMap, SymbolRef, DefinedSVal)
68 
69 void ObjCContainersChecker::addSizeInfo(const Expr *Array, const Expr *Size,
70                                         CheckerContext &C) const {
71   ProgramStateRef State = C.getState();
72   SVal SizeV = C.getSVal(Size);
73   // Undefined is reported by another checker.
74   if (SizeV.isUnknownOrUndef())
75     return;
76 
77   // Get the ArrayRef symbol.
78   SVal ArrayRef = C.getSVal(Array);
79   SymbolRef ArraySym = ArrayRef.getAsSymbol();
80   if (!ArraySym)
81     return;
82 
83   C.addTransition(
84       State->set<ArraySizeMap>(ArraySym, SizeV.castAs<DefinedSVal>()));
85 }
86 
87 void 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 
110 void 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
121     // it.
122     const Expr *ArrayExpr = CE->getArg(0);
123     SymbolRef ArraySym = getArraySym(ArrayExpr, C);
124     if (!ArraySym)
125       return;
126 
127     const DefinedSVal *Size = State->get<ArraySizeMap>(ArraySym);
128 
129     if (!Size)
130       return;
131 
132     // Get the index.
133     const Expr *IdxExpr = CE->getArg(1);
134     SVal IdxVal = C.getSVal(IdxExpr);
135     if (IdxVal.isUnknownOrUndef())
136       return;
137     DefinedSVal Idx = IdxVal.castAs<DefinedSVal>();
138 
139     // Now, check if 'Idx in [0, Size-1]'.
140     const QualType T = IdxExpr->getType();
141     ProgramStateRef StInBound = State->assumeInBound(Idx, *Size, true, T);
142     ProgramStateRef StOutBound = State->assumeInBound(Idx, *Size, false, T);
143     if (StOutBound && !StInBound) {
144       ExplodedNode *N = C.generateErrorNode(StOutBound);
145       if (!N)
146         return;
147       initBugType();
148       auto R = llvm::make_unique<BugReport>(*BT, "Index is out of bounds", N);
149       R->addRange(IdxExpr->getSourceRange());
150       bugreporter::trackExpressionValue(N, IdxExpr, *R,
151                                         /*EnableNullFPSuppression=*/false);
152       C.emitReport(std::move(R));
153       return;
154     }
155   }
156 }
157 
158 ProgramStateRef
159 ObjCContainersChecker::checkPointerEscape(ProgramStateRef State,
160                                           const InvalidatedSymbols &Escaped,
161                                           const CallEvent *Call,
162                                           PointerEscapeKind Kind) const {
163   for (const auto &Sym : Escaped) {
164     // When a symbol for a mutable array escapes, we can't reason precisely
165     // about its size any more -- so remove it from the map.
166     // Note that we aren't notified here when a CFMutableArrayRef escapes as a
167     // CFArrayRef. This is because CFArrayRef is typedef'd as a pointer to a
168     // const-qualified type.
169     State = State->remove<ArraySizeMap>(Sym);
170   }
171   return State;
172 }
173 
174 void ObjCContainersChecker::printState(raw_ostream &OS, ProgramStateRef State,
175                                        const char *NL, const char *Sep) const {
176   ArraySizeMapTy Map = State->get<ArraySizeMap>();
177   if (Map.isEmpty())
178     return;
179 
180   OS << Sep << "ObjC container sizes :" << NL;
181   for (auto I : Map) {
182     OS << I.first << " : " << I.second << NL;
183   }
184 }
185 
186 /// Register checker.
187 void ento::registerObjCContainersChecker(CheckerManager &mgr) {
188   mgr.registerChecker<ObjCContainersChecker>();
189 }
190