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;
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.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.
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 
83 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 
106 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
157 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 
172 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.
185 void ento::registerObjCContainersChecker(CheckerManager &mgr) {
186   mgr.registerChecker<ObjCContainersChecker>();
187 }
188 
189 bool ento::shouldRegisterObjCContainersChecker(const CheckerManager &mgr) {
190   return true;
191 }
192