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/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   mutable std::unique_ptr<BugType> BT;
34   inline void initBugType() const {
35     if (!BT)
36       BT.reset(new BugType(this, "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 
49 public:
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.
59 REGISTER_MAP_WITH_PROGRAMSTATE(ArraySizeMap, SymbolRef, DefinedSVal)
60 
61 void 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(
76       State->set<ArraySizeMap>(ArraySym, SizeV.castAs<DefinedSVal>()));
77   return;
78 }
79 
80 void ObjCContainersChecker::checkPostStmt(const CallExpr *CE,
81                                           CheckerContext &C) const {
82   StringRef Name = C.getCalleeName(CE);
83   if (Name.empty() || CE->getNumArgs() < 1)
84     return;
85 
86   // Add array size information to the state.
87   if (Name.equals("CFArrayCreate")) {
88     if (CE->getNumArgs() < 3)
89       return;
90     // Note, we can visit the Create method in the post-visit because
91     // the CFIndex parameter is passed in by value and will not be invalidated
92     // by the call.
93     addSizeInfo(CE, CE->getArg(2), C);
94     return;
95   }
96 
97   if (Name.equals("CFArrayGetCount")) {
98     addSizeInfo(CE->getArg(0), CE, C);
99     return;
100   }
101 }
102 
103 void ObjCContainersChecker::checkPreStmt(const CallExpr *CE,
104                                          CheckerContext &C) const {
105   StringRef Name = C.getCalleeName(CE);
106   if (Name.empty() || CE->getNumArgs() < 2)
107     return;
108 
109   // Check the array access.
110   if (Name.equals("CFArrayGetValueAtIndex")) {
111     ProgramStateRef State = C.getState();
112     // Retrieve the size.
113     // Find out if we saw this array symbol before and have information about
114     // it.
115     const Expr *ArrayExpr = CE->getArg(0);
116     SymbolRef ArraySym = getArraySym(ArrayExpr, C);
117     if (!ArraySym)
118       return;
119 
120     const DefinedSVal *Size = State->get<ArraySizeMap>(ArraySym);
121 
122     if (!Size)
123       return;
124 
125     // Get the index.
126     const Expr *IdxExpr = CE->getArg(1);
127     SVal IdxVal = State->getSVal(IdxExpr, C.getLocationContext());
128     if (IdxVal.isUnknownOrUndef())
129       return;
130     DefinedSVal Idx = IdxVal.castAs<DefinedSVal>();
131 
132     // Now, check if 'Idx in [0, Size-1]'.
133     const QualType T = IdxExpr->getType();
134     ProgramStateRef StInBound = State->assumeInBound(Idx, *Size, true, T);
135     ProgramStateRef StOutBound = State->assumeInBound(Idx, *Size, false, T);
136     if (StOutBound && !StInBound) {
137       ExplodedNode *N = C.generateSink(StOutBound);
138       if (!N)
139         return;
140       initBugType();
141       BugReport *R = new BugReport(*BT, "Index is out of bounds", N);
142       R->addRange(IdxExpr->getSourceRange());
143       C.emitReport(R);
144       return;
145     }
146   }
147 }
148 
149 /// Register checker.
150 void ento::registerObjCContainersChecker(CheckerManager &mgr) {
151   mgr.registerChecker<ObjCContainersChecker>();
152 }
153