1 //== ObjCContainersChecker.cpp - Path sensitive checker for CFArray *- C++ -*=//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // Performs path sensitive checks of Core Foundation static containers like
10 // CFArray.
11 // 1) Check for buffer overflows:
12 // In CFArrayGetArrayAtIndex( myArray, index), if the index is outside the
13 // index space of theArray (0 to N-1 inclusive (where N is the count of
14 // theArray), the behavior is undefined.
15 //
16 //===----------------------------------------------------------------------===//
17
18 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
19 #include "clang/AST/ParentMap.h"
20 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
21 #include "clang/StaticAnalyzer/Core/Checker.h"
22 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
23 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
24 #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramStateTrait.h"
25
26 using namespace clang;
27 using namespace ento;
28
29 namespace {
30 class ObjCContainersChecker : public Checker< check::PreStmt<CallExpr>,
31 check::PostStmt<CallExpr>,
32 check::PointerEscape> {
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.getSVal(E);
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 ProgramStateRef checkPointerEscape(ProgramStateRef State,
56 const InvalidatedSymbols &Escaped,
57 const CallEvent *Call,
58 PointerEscapeKind Kind) const;
59
60 void printState(raw_ostream &OS, ProgramStateRef State,
61 const char *NL, const char *Sep) const override;
62 };
63 } // end anonymous namespace
64
65 // ProgramState trait - a map from array symbol to its state.
REGISTER_MAP_WITH_PROGRAMSTATE(ArraySizeMap,SymbolRef,DefinedSVal)66 REGISTER_MAP_WITH_PROGRAMSTATE(ArraySizeMap, SymbolRef, DefinedSVal)
67
68 void ObjCContainersChecker::addSizeInfo(const Expr *Array, const Expr *Size,
69 CheckerContext &C) const {
70 ProgramStateRef State = C.getState();
71 SVal SizeV = C.getSVal(Size);
72 // Undefined is reported by another checker.
73 if (SizeV.isUnknownOrUndef())
74 return;
75
76 // Get the ArrayRef symbol.
77 SVal ArrayRef = C.getSVal(Array);
78 SymbolRef ArraySym = ArrayRef.getAsSymbol();
79 if (!ArraySym)
80 return;
81
82 C.addTransition(
83 State->set<ArraySizeMap>(ArraySym, SizeV.castAs<DefinedSVal>()));
84 }
85
checkPostStmt(const CallExpr * CE,CheckerContext & C) const86 void ObjCContainersChecker::checkPostStmt(const CallExpr *CE,
87 CheckerContext &C) const {
88 StringRef Name = C.getCalleeName(CE);
89 if (Name.empty() || CE->getNumArgs() < 1)
90 return;
91
92 // Add array size information to the state.
93 if (Name.equals("CFArrayCreate")) {
94 if (CE->getNumArgs() < 3)
95 return;
96 // Note, we can visit the Create method in the post-visit because
97 // the CFIndex parameter is passed in by value and will not be invalidated
98 // by the call.
99 addSizeInfo(CE, CE->getArg(2), C);
100 return;
101 }
102
103 if (Name.equals("CFArrayGetCount")) {
104 addSizeInfo(CE->getArg(0), CE, C);
105 return;
106 }
107 }
108
checkPreStmt(const CallExpr * CE,CheckerContext & C) const109 void ObjCContainersChecker::checkPreStmt(const CallExpr *CE,
110 CheckerContext &C) const {
111 StringRef Name = C.getCalleeName(CE);
112 if (Name.empty() || CE->getNumArgs() < 2)
113 return;
114
115 // Check the array access.
116 if (Name.equals("CFArrayGetValueAtIndex")) {
117 ProgramStateRef State = C.getState();
118 // Retrieve the size.
119 // Find out if we saw this array symbol before and have information about
120 // 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 = C.getSVal(IdxExpr);
134 if (IdxVal.isUnknownOrUndef())
135 return;
136 DefinedSVal Idx = IdxVal.castAs<DefinedSVal>();
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.generateErrorNode(StOutBound);
144 if (!N)
145 return;
146 initBugType();
147 auto R = std::make_unique<PathSensitiveBugReport>(
148 *BT, "Index is out of bounds", N);
149 R->addRange(IdxExpr->getSourceRange());
150 bugreporter::trackExpressionValue(
151 N, IdxExpr, *R, bugreporter::TrackingKind::Thorough, false);
152 C.emitReport(std::move(R));
153 return;
154 }
155 }
156 }
157
158 ProgramStateRef
checkPointerEscape(ProgramStateRef State,const InvalidatedSymbols & Escaped,const CallEvent * Call,PointerEscapeKind Kind) const159 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
printState(raw_ostream & OS,ProgramStateRef State,const char * NL,const char * Sep) const174 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.
registerObjCContainersChecker(CheckerManager & mgr)187 void ento::registerObjCContainersChecker(CheckerManager &mgr) {
188 mgr.registerChecker<ObjCContainersChecker>();
189 }
190
shouldRegisterObjCContainersChecker(const CheckerManager & mgr)191 bool ento::shouldRegisterObjCContainersChecker(const CheckerManager &mgr) {
192 return true;
193 }
194