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 void checkPostStmt(const CallExpr *CE, CheckerContext &C) const;
51 void checkPreStmt(const CallExpr *CE, CheckerContext &C) const;
52 ProgramStateRef checkPointerEscape(ProgramStateRef State,
53 const InvalidatedSymbols &Escaped,
54 const CallEvent *Call,
55 PointerEscapeKind Kind) const;
56
57 void printState(raw_ostream &OS, ProgramStateRef State,
58 const char *NL, const char *Sep) const override;
59 };
60 } // end anonymous namespace
61
62 // ProgramState trait - a map from array symbol to its state.
REGISTER_MAP_WITH_PROGRAMSTATE(ArraySizeMap,SymbolRef,DefinedSVal)63 REGISTER_MAP_WITH_PROGRAMSTATE(ArraySizeMap, SymbolRef, DefinedSVal)
64
65 void ObjCContainersChecker::addSizeInfo(const Expr *Array, const Expr *Size,
66 CheckerContext &C) const {
67 ProgramStateRef State = C.getState();
68 SVal SizeV = C.getSVal(Size);
69 // Undefined is reported by another checker.
70 if (SizeV.isUnknownOrUndef())
71 return;
72
73 // Get the ArrayRef symbol.
74 SVal ArrayRef = C.getSVal(Array);
75 SymbolRef ArraySym = ArrayRef.getAsSymbol();
76 if (!ArraySym)
77 return;
78
79 C.addTransition(
80 State->set<ArraySizeMap>(ArraySym, SizeV.castAs<DefinedSVal>()));
81 }
82
checkPostStmt(const CallExpr * CE,CheckerContext & C) const83 void ObjCContainersChecker::checkPostStmt(const CallExpr *CE,
84 CheckerContext &C) const {
85 StringRef Name = C.getCalleeName(CE);
86 if (Name.empty() || CE->getNumArgs() < 1)
87 return;
88
89 // Add array size information to the state.
90 if (Name.equals("CFArrayCreate")) {
91 if (CE->getNumArgs() < 3)
92 return;
93 // Note, we can visit the Create method in the post-visit because
94 // the CFIndex parameter is passed in by value and will not be invalidated
95 // by the call.
96 addSizeInfo(CE, CE->getArg(2), C);
97 return;
98 }
99
100 if (Name.equals("CFArrayGetCount")) {
101 addSizeInfo(CE->getArg(0), CE, C);
102 return;
103 }
104 }
105
checkPreStmt(const CallExpr * CE,CheckerContext & C) const106 void ObjCContainersChecker::checkPreStmt(const CallExpr *CE,
107 CheckerContext &C) const {
108 StringRef Name = C.getCalleeName(CE);
109 if (Name.empty() || CE->getNumArgs() < 2)
110 return;
111
112 // Check the array access.
113 if (Name.equals("CFArrayGetValueAtIndex")) {
114 ProgramStateRef State = C.getState();
115 // Retrieve the size.
116 // Find out if we saw this array symbol before and have information about
117 // it.
118 const Expr *ArrayExpr = CE->getArg(0);
119 SymbolRef ArraySym = getArraySym(ArrayExpr, C);
120 if (!ArraySym)
121 return;
122
123 const DefinedSVal *Size = State->get<ArraySizeMap>(ArraySym);
124
125 if (!Size)
126 return;
127
128 // Get the index.
129 const Expr *IdxExpr = CE->getArg(1);
130 SVal IdxVal = C.getSVal(IdxExpr);
131 if (IdxVal.isUnknownOrUndef())
132 return;
133 DefinedSVal Idx = IdxVal.castAs<DefinedSVal>();
134
135 // Now, check if 'Idx in [0, Size-1]'.
136 const QualType T = IdxExpr->getType();
137 ProgramStateRef StInBound, StOutBound;
138 std::tie(StInBound, StOutBound) = State->assumeInBoundDual(Idx, *Size, T);
139 if (StOutBound && !StInBound) {
140 ExplodedNode *N = C.generateErrorNode(StOutBound);
141 if (!N)
142 return;
143 initBugType();
144 auto R = std::make_unique<PathSensitiveBugReport>(
145 *BT, "Index is out of bounds", N);
146 R->addRange(IdxExpr->getSourceRange());
147 bugreporter::trackExpressionValue(N, IdxExpr, *R,
148 {bugreporter::TrackingKind::Thorough,
149 /*EnableNullFPSuppression=*/false});
150 C.emitReport(std::move(R));
151 return;
152 }
153 }
154 }
155
156 ProgramStateRef
checkPointerEscape(ProgramStateRef State,const InvalidatedSymbols & Escaped,const CallEvent * Call,PointerEscapeKind Kind) const157 ObjCContainersChecker::checkPointerEscape(ProgramStateRef State,
158 const InvalidatedSymbols &Escaped,
159 const CallEvent *Call,
160 PointerEscapeKind Kind) const {
161 for (const auto &Sym : Escaped) {
162 // When a symbol for a mutable array escapes, we can't reason precisely
163 // about its size any more -- so remove it from the map.
164 // Note that we aren't notified here when a CFMutableArrayRef escapes as a
165 // CFArrayRef. This is because CFArrayRef is typedef'd as a pointer to a
166 // const-qualified type.
167 State = State->remove<ArraySizeMap>(Sym);
168 }
169 return State;
170 }
171
printState(raw_ostream & OS,ProgramStateRef State,const char * NL,const char * Sep) const172 void ObjCContainersChecker::printState(raw_ostream &OS, ProgramStateRef State,
173 const char *NL, const char *Sep) const {
174 ArraySizeMapTy Map = State->get<ArraySizeMap>();
175 if (Map.isEmpty())
176 return;
177
178 OS << Sep << "ObjC container sizes :" << NL;
179 for (auto I : Map) {
180 OS << I.first << " : " << I.second << NL;
181 }
182 }
183
184 /// Register checker.
registerObjCContainersChecker(CheckerManager & mgr)185 void ento::registerObjCContainersChecker(CheckerManager &mgr) {
186 mgr.registerChecker<ObjCContainersChecker>();
187 }
188
shouldRegisterObjCContainersChecker(const CheckerManager & mgr)189 bool ento::shouldRegisterObjCContainersChecker(const CheckerManager &mgr) {
190 return true;
191 }
192