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
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 OwningPtr<BugType> BT;
initBugType() const34 inline void initBugType() const {
35 if (!BT)
36 BT.reset(new BugType("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 it's state.
59 typedef llvm::ImmutableMap<SymbolRef, DefinedSVal> ArraySizeM;
60
61 namespace { struct ArraySizeMap {}; }
62 namespace clang { namespace ento {
63 template<> struct ProgramStateTrait<ArraySizeMap>
64 : public ProgramStatePartialTrait<ArraySizeM > {
GDMIndexclang::ento::ProgramStateTrait65 static void *GDMIndex() { return ObjCContainersChecker::getTag(); }
66 };
67 }}
68
addSizeInfo(const Expr * Array,const Expr * Size,CheckerContext & C) const69 void 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
checkPostStmt(const CallExpr * CE,CheckerContext & C) const87 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
checkPreStmt(const CallExpr * CE,CheckerContext & C) const110 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 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.
registerObjCContainersChecker(CheckerManager & mgr)156 void ento::registerObjCContainersChecker(CheckerManager &mgr) {
157 mgr.registerChecker<ObjCContainersChecker>();
158 }
159