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;
initBugType() const34 inline void initBugType() const {
35 if (!BT)
36 BT.reset(new BugType(this, "CFArray API",
37 categories::CoreFoundationObjectiveC));
38 }
39
getArraySym(const Expr * E,CheckerContext & C) const40 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.
getTag()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.
REGISTER_MAP_WITH_PROGRAMSTATE(ArraySizeMap,SymbolRef,DefinedSVal)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
checkPostStmt(const CallExpr * CE,CheckerContext & C) const80 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
checkPreStmt(const CallExpr * CE,CheckerContext & C) const103 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 it.
114 const Expr *ArrayExpr = CE->getArg(0);
115 SymbolRef ArraySym = getArraySym(ArrayExpr, C);
116 if (!ArraySym)
117 return;
118
119 const DefinedSVal *Size = State->get<ArraySizeMap>(ArraySym);
120
121 if (!Size)
122 return;
123
124 // Get the index.
125 const Expr *IdxExpr = CE->getArg(1);
126 SVal IdxVal = State->getSVal(IdxExpr, C.getLocationContext());
127 if (IdxVal.isUnknownOrUndef())
128 return;
129 DefinedSVal Idx = IdxVal.castAs<DefinedSVal>();
130
131 // Now, check if 'Idx in [0, Size-1]'.
132 const QualType T = IdxExpr->getType();
133 ProgramStateRef StInBound = State->assumeInBound(Idx, *Size, true, T);
134 ProgramStateRef StOutBound = State->assumeInBound(Idx, *Size, false, T);
135 if (StOutBound && !StInBound) {
136 ExplodedNode *N = C.generateSink(StOutBound);
137 if (!N)
138 return;
139 initBugType();
140 BugReport *R = new BugReport(*BT, "Index is out of bounds", N);
141 R->addRange(IdxExpr->getSourceRange());
142 C.emitReport(R);
143 return;
144 }
145 }
146 }
147
148 /// Register checker.
registerObjCContainersChecker(CheckerManager & mgr)149 void ento::registerObjCContainersChecker(CheckerManager &mgr) {
150 mgr.registerChecker<ObjCContainersChecker>();
151 }
152