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 
28 using namespace clang;
29 using namespace ento;
30 
31 namespace {
32 class ObjCContainersChecker : public Checker< check::PreStmt<CallExpr>,
33                                              check::PostStmt<CallExpr> > {
34   mutable OwningPtr<BugType> BT;
35   inline void initBugType() const {
36     if (!BT)
37       BT.reset(new BugType("CFArray API", "Core Foundation/Objective-C"));
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 
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 };
57 } // end anonymous namespace
58 
59 // ProgramState trait - a map from array symbol to it's state.
60 typedef llvm::ImmutableMap<SymbolRef, DefinedSVal> ArraySizeM;
61 
62 namespace { struct ArraySizeMap {}; }
63 namespace clang { namespace ento {
64 template<> struct ProgramStateTrait<ArraySizeMap>
65     :  public ProgramStatePartialTrait<ArraySizeM > {
66   static void *GDMIndex() { return ObjCContainersChecker::getTag(); }
67 };
68 }}
69 
70 void ObjCContainersChecker::addSizeInfo(const Expr *Array, const Expr *Size,
71                                         CheckerContext &C) const {
72   ProgramStateRef State = C.getState();
73   SVal SizeV = State->getSVal(Size, C.getLocationContext());
74   // Undefined is reported by another checker.
75   if (SizeV.isUnknownOrUndef())
76     return;
77 
78   // Get the ArrayRef symbol.
79   SVal ArrayRef = State->getSVal(Array, C.getLocationContext());
80   SymbolRef ArraySym = ArrayRef.getAsSymbol();
81   if (!ArraySym)
82     return;
83 
84   C.addTransition(State->set<ArraySizeMap>(ArraySym, cast<DefinedSVal>(SizeV)));
85   return;
86 }
87 
88 void ObjCContainersChecker::checkPostStmt(const CallExpr *CE,
89                                           CheckerContext &C) const {
90   StringRef Name = C.getCalleeName(CE);
91   if (Name.empty() || CE->getNumArgs() < 1)
92     return;
93 
94   // Add array size information to the state.
95   if (Name.equals("CFArrayCreate")) {
96     if (CE->getNumArgs() < 3)
97       return;
98     // Note, we can visit the Create method in the post-visit because
99     // the CFIndex parameter is passed in by value and will not be invalidated
100     // by the call.
101     addSizeInfo(CE, CE->getArg(2), C);
102     return;
103   }
104 
105   if (Name.equals("CFArrayGetCount")) {
106     addSizeInfo(CE->getArg(0), CE, C);
107     return;
108   }
109 }
110 
111 void ObjCContainersChecker::checkPreStmt(const CallExpr *CE,
112                                          CheckerContext &C) const {
113   StringRef Name = C.getCalleeName(CE);
114   if (Name.empty() || CE->getNumArgs() < 2)
115     return;
116 
117   // Check the array access.
118   if (Name.equals("CFArrayGetValueAtIndex")) {
119     ProgramStateRef State = C.getState();
120     // Retrieve the size.
121     // Find out if we saw this array symbol before and have information about it.
122     const Expr *ArrayExpr = CE->getArg(0);
123     const DefinedSVal *Size =
124                             State->get<ArraySizeMap>(getArraySym(ArrayExpr, C));
125     if (!Size)
126       return;
127 
128     // Get the index.
129     const Expr *IdxExpr = CE->getArg(1);
130     SVal IdxVal = State->getSVal(IdxExpr, C.getLocationContext());
131     if (IdxVal.isUnknownOrUndef())
132       return;
133     DefinedSVal Idx = cast<DefinedSVal>(IdxVal);
134 
135     // Now, check if 'Idx in [0, Size-1]'.
136     const QualType T = IdxExpr->getType();
137     ProgramStateRef StInBound = State->assumeInBound(Idx, *Size, true, T);
138     ProgramStateRef StOutBound = State->assumeInBound(Idx, *Size, false, T);
139     if (StOutBound && !StInBound) {
140       ExplodedNode *N = C.generateSink(StOutBound);
141       if (!N)
142         return;
143       initBugType();
144       BugReport *R = new BugReport(*BT, "Index is out of bounds", N);
145       R->addRange(IdxExpr->getSourceRange());
146       C.EmitReport(R);
147       return;
148     }
149   }
150 }
151 
152 /// Register checker.
153 void ento::registerObjCContainersChecker(CheckerManager &mgr) {
154   mgr.registerChecker<ObjCContainersChecker>();
155 }
156