1 //===-- IteratorRangeChecker.cpp ----------------------------------*- 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 // Defines a checker for dereference of the past-the-end iterator and
10 // out-of-range increments and decrements.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
15 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
16 #include "clang/StaticAnalyzer/Core/Checker.h"
17 #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
18 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
19 
20 
21 #include "Iterator.h"
22 
23 using namespace clang;
24 using namespace ento;
25 using namespace iterator;
26 
27 namespace {
28 
29 class IteratorRangeChecker
30   : public Checker<check::PreCall> {
31 
32   std::unique_ptr<BugType> OutOfRangeBugType;
33 
34   void verifyDereference(CheckerContext &C, const SVal &Val) const;
35   void verifyIncrement(CheckerContext &C, const SVal &Iter) const;
36   void verifyDecrement(CheckerContext &C, const SVal &Iter) const;
37   void verifyRandomIncrOrDecr(CheckerContext &C, OverloadedOperatorKind Op,
38                               const SVal &LHS, const SVal &RHS) const;
39   void reportBug(const StringRef &Message, const SVal &Val,
40                  CheckerContext &C, ExplodedNode *ErrNode) const;
41 public:
42   IteratorRangeChecker();
43 
44   void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
45 
46 };
47 
48 bool isPastTheEnd(ProgramStateRef State, const IteratorPosition &Pos);
49 bool isAheadOfRange(ProgramStateRef State, const IteratorPosition &Pos);
50 bool isBehindPastTheEnd(ProgramStateRef State, const IteratorPosition &Pos);
51 bool isZero(ProgramStateRef State, const NonLoc &Val);
52 
53 } //namespace
54 
55 IteratorRangeChecker::IteratorRangeChecker() {
56   OutOfRangeBugType.reset(
57       new BugType(this, "Iterator out of range", "Misuse of STL APIs"));
58 }
59 
60 void IteratorRangeChecker::checkPreCall(const CallEvent &Call,
61                                         CheckerContext &C) const {
62   // Check for out of range access
63   const auto *Func = dyn_cast_or_null<FunctionDecl>(Call.getDecl());
64   if (!Func)
65     return;
66 
67   if (Func->isOverloadedOperator()) {
68     if (isIncrementOperator(Func->getOverloadedOperator())) {
69       // Check for out-of-range incrementions
70       if (const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call)) {
71         verifyIncrement(C, InstCall->getCXXThisVal());
72       } else {
73         if (Call.getNumArgs() >= 1) {
74           verifyIncrement(C, Call.getArgSVal(0));
75         }
76       }
77     } else if (isDecrementOperator(Func->getOverloadedOperator())) {
78       // Check for out-of-range decrementions
79       if (const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call)) {
80         verifyDecrement(C, InstCall->getCXXThisVal());
81       } else {
82         if (Call.getNumArgs() >= 1) {
83           verifyDecrement(C, Call.getArgSVal(0));
84         }
85       }
86     } else if (isRandomIncrOrDecrOperator(Func->getOverloadedOperator())) {
87       if (const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call)) {
88         // Check for out-of-range incrementions and decrementions
89         if (Call.getNumArgs() >= 1 &&
90             Call.getArgExpr(0)->getType()->isIntegralOrEnumerationType()) {
91           verifyRandomIncrOrDecr(C, Func->getOverloadedOperator(),
92                                  InstCall->getCXXThisVal(),
93                                  Call.getArgSVal(0));
94         }
95       } else {
96         if (Call.getNumArgs() >= 2 &&
97             Call.getArgExpr(1)->getType()->isIntegralOrEnumerationType()) {
98           verifyRandomIncrOrDecr(C, Func->getOverloadedOperator(),
99                                  Call.getArgSVal(0), Call.getArgSVal(1));
100         }
101       }
102     } else if (isDereferenceOperator(Func->getOverloadedOperator())) {
103       // Check for dereference of out-of-range iterators
104       if (const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call)) {
105         verifyDereference(C, InstCall->getCXXThisVal());
106       } else {
107         verifyDereference(C, Call.getArgSVal(0));
108       }
109     }
110   }
111 }
112 
113 void IteratorRangeChecker::verifyDereference(CheckerContext &C,
114                                              const SVal &Val) const {
115   auto State = C.getState();
116   const auto *Pos = getIteratorPosition(State, Val);
117   if (Pos && isPastTheEnd(State, *Pos)) {
118     auto *N = C.generateErrorNode(State);
119     if (!N)
120       return;
121     reportBug("Past-the-end iterator dereferenced.", Val, C, N);
122     return;
123   }
124 }
125 
126 void IteratorRangeChecker::verifyIncrement(CheckerContext &C,
127                                           const SVal &Iter) const {
128   auto &BVF = C.getSValBuilder().getBasicValueFactory();
129   verifyRandomIncrOrDecr(C, OO_Plus, Iter,
130                      nonloc::ConcreteInt(BVF.getValue(llvm::APSInt::get(1))));
131 }
132 
133 void IteratorRangeChecker::verifyDecrement(CheckerContext &C,
134                                           const SVal &Iter) const {
135   auto &BVF = C.getSValBuilder().getBasicValueFactory();
136   verifyRandomIncrOrDecr(C, OO_Minus, Iter,
137                      nonloc::ConcreteInt(BVF.getValue(llvm::APSInt::get(1))));
138 }
139 
140 void IteratorRangeChecker::verifyRandomIncrOrDecr(CheckerContext &C,
141                                                  OverloadedOperatorKind Op,
142                                                  const SVal &LHS,
143                                                  const SVal &RHS) const {
144   auto State = C.getState();
145 
146   auto Value = RHS;
147   if (auto ValAsLoc = RHS.getAs<Loc>()) {
148     Value = State->getRawSVal(*ValAsLoc);
149   }
150 
151   if (Value.isUnknown())
152     return;
153 
154   // Incremention or decremention by 0 is never a bug.
155   if (isZero(State, Value.castAs<NonLoc>()))
156     return;
157 
158   // The result may be the past-end iterator of the container, but any other
159   // out of range position is undefined behaviour
160   auto StateAfter = advancePosition(State, LHS, Op, Value);
161   if (!StateAfter)
162     return;
163 
164   const auto *PosAfter = getIteratorPosition(StateAfter, LHS);
165   assert(PosAfter &&
166          "Iterator should have position after successful advancement");
167   if (isAheadOfRange(State, *PosAfter)) {
168     auto *N = C.generateErrorNode(State);
169     if (!N)
170       return;
171     reportBug("Iterator decremented ahead of its valid range.", LHS,
172                         C, N);
173   }
174   if (isBehindPastTheEnd(State, *PosAfter)) {
175     auto *N = C.generateErrorNode(State);
176     if (!N)
177       return;
178     reportBug("Iterator incremented behind the past-the-end "
179                         "iterator.", LHS, C, N);
180   }
181 }
182 
183 void IteratorRangeChecker::reportBug(const StringRef &Message,
184                                     const SVal &Val, CheckerContext &C,
185                                     ExplodedNode *ErrNode) const {
186   auto R = std::make_unique<PathSensitiveBugReport>(*OutOfRangeBugType, Message,
187                                                     ErrNode);
188   R->markInteresting(Val);
189   C.emitReport(std::move(R));
190 }
191 
192 namespace {
193 
194 bool isLess(ProgramStateRef State, SymbolRef Sym1, SymbolRef Sym2);
195 bool isGreater(ProgramStateRef State, SymbolRef Sym1, SymbolRef Sym2);
196 bool isEqual(ProgramStateRef State, SymbolRef Sym1, SymbolRef Sym2);
197 
198 bool isZero(ProgramStateRef State, const NonLoc &Val) {
199   auto &BVF = State->getBasicVals();
200   return compare(State, Val,
201                  nonloc::ConcreteInt(BVF.getValue(llvm::APSInt::get(0))),
202                  BO_EQ);
203 }
204 
205 bool isPastTheEnd(ProgramStateRef State, const IteratorPosition &Pos) {
206   const auto *Cont = Pos.getContainer();
207   const auto *CData = getContainerData(State, Cont);
208   if (!CData)
209     return false;
210 
211   const auto End = CData->getEnd();
212   if (End) {
213     if (isEqual(State, Pos.getOffset(), End)) {
214       return true;
215     }
216   }
217 
218   return false;
219 }
220 
221 bool isAheadOfRange(ProgramStateRef State, const IteratorPosition &Pos) {
222   const auto *Cont = Pos.getContainer();
223   const auto *CData = getContainerData(State, Cont);
224   if (!CData)
225     return false;
226 
227   const auto Beg = CData->getBegin();
228   if (Beg) {
229     if (isLess(State, Pos.getOffset(), Beg)) {
230       return true;
231     }
232   }
233 
234   return false;
235 }
236 
237 bool isBehindPastTheEnd(ProgramStateRef State, const IteratorPosition &Pos) {
238   const auto *Cont = Pos.getContainer();
239   const auto *CData = getContainerData(State, Cont);
240   if (!CData)
241     return false;
242 
243   const auto End = CData->getEnd();
244   if (End) {
245     if (isGreater(State, Pos.getOffset(), End)) {
246       return true;
247     }
248   }
249 
250   return false;
251 }
252 
253 bool isLess(ProgramStateRef State, SymbolRef Sym1, SymbolRef Sym2) {
254   return compare(State, Sym1, Sym2, BO_LT);
255 }
256 
257 bool isGreater(ProgramStateRef State, SymbolRef Sym1, SymbolRef Sym2) {
258   return compare(State, Sym1, Sym2, BO_GT);
259 }
260 
261 bool isEqual(ProgramStateRef State, SymbolRef Sym1, SymbolRef Sym2) {
262   return compare(State, Sym1, Sym2, BO_EQ);
263 }
264 
265 } // namespace
266 
267 void ento::registerIteratorRangeChecker(CheckerManager &mgr) {
268   mgr.registerChecker<IteratorRangeChecker>();
269 }
270 
271 bool ento::shouldRegisterIteratorRangeChecker(const LangOptions &LO) {
272   return true;
273 }
274