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/CallDescription.h"
18 #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
19 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
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, check::PreStmt<UnaryOperator>,
31                    check::PreStmt<BinaryOperator>,
32                    check::PreStmt<ArraySubscriptExpr>,
33                    check::PreStmt<MemberExpr>> {
34 
35   std::unique_ptr<BugType> OutOfRangeBugType;
36 
37   void verifyDereference(CheckerContext &C, SVal Val) const;
38   void verifyIncrement(CheckerContext &C, SVal Iter) const;
39   void verifyDecrement(CheckerContext &C, SVal Iter) const;
40   void verifyRandomIncrOrDecr(CheckerContext &C, OverloadedOperatorKind Op,
41                               SVal LHS, SVal RHS) const;
42   void verifyAdvance(CheckerContext &C, SVal LHS, SVal RHS) const;
43   void verifyPrev(CheckerContext &C, SVal LHS, SVal RHS) const;
44   void verifyNext(CheckerContext &C, SVal LHS, SVal RHS) const;
45   void reportBug(const StringRef &Message, SVal Val, CheckerContext &C,
46                  ExplodedNode *ErrNode) const;
47 
48 public:
49   IteratorRangeChecker();
50 
51   void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
52   void checkPreStmt(const UnaryOperator *UO, CheckerContext &C) const;
53   void checkPreStmt(const BinaryOperator *BO, CheckerContext &C) const;
54   void checkPreStmt(const ArraySubscriptExpr *ASE, CheckerContext &C) const;
55   void checkPreStmt(const MemberExpr *ME, CheckerContext &C) const;
56 
57   using AdvanceFn = void (IteratorRangeChecker::*)(CheckerContext &, SVal,
58                                                    SVal) const;
59 
60   CallDescriptionMap<AdvanceFn> AdvanceFunctions = {
61       {{{"std", "advance"}, 2}, &IteratorRangeChecker::verifyAdvance},
62       {{{"std", "prev"}, 2}, &IteratorRangeChecker::verifyPrev},
63       {{{"std", "next"}, 2}, &IteratorRangeChecker::verifyNext},
64   };
65 };
66 
67 bool isPastTheEnd(ProgramStateRef State, const IteratorPosition &Pos);
68 bool isAheadOfRange(ProgramStateRef State, const IteratorPosition &Pos);
69 bool isBehindPastTheEnd(ProgramStateRef State, const IteratorPosition &Pos);
70 bool isZero(ProgramStateRef State, const NonLoc &Val);
71 
72 } //namespace
73 
IteratorRangeChecker()74 IteratorRangeChecker::IteratorRangeChecker() {
75   OutOfRangeBugType.reset(
76       new BugType(this, "Iterator out of range", "Misuse of STL APIs"));
77 }
78 
checkPreCall(const CallEvent & Call,CheckerContext & C) const79 void IteratorRangeChecker::checkPreCall(const CallEvent &Call,
80                                         CheckerContext &C) const {
81   // Check for out of range access
82   const auto *Func = dyn_cast_or_null<FunctionDecl>(Call.getDecl());
83   if (!Func)
84     return;
85 
86   if (Func->isOverloadedOperator()) {
87     if (isIncrementOperator(Func->getOverloadedOperator())) {
88       // Check for out-of-range incrementions
89       if (const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call)) {
90         verifyIncrement(C, InstCall->getCXXThisVal());
91       } else {
92         if (Call.getNumArgs() >= 1) {
93           verifyIncrement(C, Call.getArgSVal(0));
94         }
95       }
96     } else if (isDecrementOperator(Func->getOverloadedOperator())) {
97       // Check for out-of-range decrementions
98       if (const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call)) {
99         verifyDecrement(C, InstCall->getCXXThisVal());
100       } else {
101         if (Call.getNumArgs() >= 1) {
102           verifyDecrement(C, Call.getArgSVal(0));
103         }
104       }
105     } else if (isRandomIncrOrDecrOperator(Func->getOverloadedOperator())) {
106       if (const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call)) {
107         // Check for out-of-range incrementions and decrementions
108         if (Call.getNumArgs() >= 1 &&
109             Call.getArgExpr(0)->getType()->isIntegralOrEnumerationType()) {
110           verifyRandomIncrOrDecr(C, Func->getOverloadedOperator(),
111                                  InstCall->getCXXThisVal(),
112                                  Call.getArgSVal(0));
113         }
114       } else {
115         if (Call.getNumArgs() >= 2 &&
116             Call.getArgExpr(1)->getType()->isIntegralOrEnumerationType()) {
117           verifyRandomIncrOrDecr(C, Func->getOverloadedOperator(),
118                                  Call.getArgSVal(0), Call.getArgSVal(1));
119         }
120       }
121     } else if (isDereferenceOperator(Func->getOverloadedOperator())) {
122       // Check for dereference of out-of-range iterators
123       if (const auto *InstCall = dyn_cast<CXXInstanceCall>(&Call)) {
124         verifyDereference(C, InstCall->getCXXThisVal());
125       } else {
126         verifyDereference(C, Call.getArgSVal(0));
127       }
128     }
129   } else {
130     const AdvanceFn *Verifier = AdvanceFunctions.lookup(Call);
131     if (Verifier) {
132       if (Call.getNumArgs() > 1) {
133         (this->**Verifier)(C, Call.getArgSVal(0), Call.getArgSVal(1));
134       } else {
135         auto &BVF = C.getSValBuilder().getBasicValueFactory();
136         (this->**Verifier)(
137             C, Call.getArgSVal(0),
138             nonloc::ConcreteInt(BVF.getValue(llvm::APSInt::get(1))));
139       }
140     }
141   }
142 }
143 
checkPreStmt(const UnaryOperator * UO,CheckerContext & C) const144 void IteratorRangeChecker::checkPreStmt(const UnaryOperator *UO,
145                                         CheckerContext &C) const {
146   if (isa<CXXThisExpr>(UO->getSubExpr()))
147     return;
148 
149   ProgramStateRef State = C.getState();
150   UnaryOperatorKind OK = UO->getOpcode();
151   SVal SubVal = State->getSVal(UO->getSubExpr(), C.getLocationContext());
152 
153   if (isDereferenceOperator(OK)) {
154     verifyDereference(C, SubVal);
155   } else if (isIncrementOperator(OK)) {
156     verifyIncrement(C, SubVal);
157   } else if (isDecrementOperator(OK)) {
158     verifyDecrement(C, SubVal);
159   }
160 }
161 
checkPreStmt(const BinaryOperator * BO,CheckerContext & C) const162 void IteratorRangeChecker::checkPreStmt(const BinaryOperator *BO,
163                                         CheckerContext &C) const {
164   ProgramStateRef State = C.getState();
165   BinaryOperatorKind OK = BO->getOpcode();
166   SVal LVal = State->getSVal(BO->getLHS(), C.getLocationContext());
167 
168   if (isDereferenceOperator(OK)) {
169     verifyDereference(C, LVal);
170   } else if (isRandomIncrOrDecrOperator(OK)) {
171     SVal RVal = State->getSVal(BO->getRHS(), C.getLocationContext());
172     if (!BO->getRHS()->getType()->isIntegralOrEnumerationType())
173       return;
174     verifyRandomIncrOrDecr(C, BinaryOperator::getOverloadedOperator(OK), LVal,
175                            RVal);
176   }
177 }
178 
checkPreStmt(const ArraySubscriptExpr * ASE,CheckerContext & C) const179 void IteratorRangeChecker::checkPreStmt(const ArraySubscriptExpr *ASE,
180                                         CheckerContext &C) const {
181   ProgramStateRef State = C.getState();
182   SVal LVal = State->getSVal(ASE->getLHS(), C.getLocationContext());
183   verifyDereference(C, LVal);
184 }
185 
checkPreStmt(const MemberExpr * ME,CheckerContext & C) const186 void IteratorRangeChecker::checkPreStmt(const MemberExpr *ME,
187                                         CheckerContext &C) const {
188   if (!ME->isArrow() || ME->isImplicitAccess())
189     return;
190 
191   ProgramStateRef State = C.getState();
192   SVal BaseVal = State->getSVal(ME->getBase(), C.getLocationContext());
193   verifyDereference(C, BaseVal);
194 }
195 
verifyDereference(CheckerContext & C,SVal Val) const196 void IteratorRangeChecker::verifyDereference(CheckerContext &C,
197                                              SVal Val) const {
198   auto State = C.getState();
199   const auto *Pos = getIteratorPosition(State, Val);
200   if (Pos && isPastTheEnd(State, *Pos)) {
201     auto *N = C.generateErrorNode(State);
202     if (!N)
203       return;
204     reportBug("Past-the-end iterator dereferenced.", Val, C, N);
205     return;
206   }
207 }
208 
verifyIncrement(CheckerContext & C,SVal Iter) const209 void IteratorRangeChecker::verifyIncrement(CheckerContext &C, SVal Iter) const {
210   auto &BVF = C.getSValBuilder().getBasicValueFactory();
211   verifyRandomIncrOrDecr(C, OO_Plus, Iter,
212                      nonloc::ConcreteInt(BVF.getValue(llvm::APSInt::get(1))));
213 }
214 
verifyDecrement(CheckerContext & C,SVal Iter) const215 void IteratorRangeChecker::verifyDecrement(CheckerContext &C, SVal Iter) const {
216   auto &BVF = C.getSValBuilder().getBasicValueFactory();
217   verifyRandomIncrOrDecr(C, OO_Minus, Iter,
218                      nonloc::ConcreteInt(BVF.getValue(llvm::APSInt::get(1))));
219 }
220 
verifyRandomIncrOrDecr(CheckerContext & C,OverloadedOperatorKind Op,SVal LHS,SVal RHS) const221 void IteratorRangeChecker::verifyRandomIncrOrDecr(CheckerContext &C,
222                                                   OverloadedOperatorKind Op,
223                                                   SVal LHS, SVal RHS) const {
224   auto State = C.getState();
225 
226   auto Value = RHS;
227   if (auto ValAsLoc = RHS.getAs<Loc>()) {
228     Value = State->getRawSVal(*ValAsLoc);
229   }
230 
231   if (Value.isUnknownOrUndef())
232     return;
233 
234   // Incremention or decremention by 0 is never a bug.
235   if (isZero(State, Value.castAs<NonLoc>()))
236     return;
237 
238   // The result may be the past-end iterator of the container, but any other
239   // out of range position is undefined behaviour
240   auto StateAfter = advancePosition(State, LHS, Op, Value);
241   if (!StateAfter)
242     return;
243 
244   const auto *PosAfter = getIteratorPosition(StateAfter, LHS);
245   assert(PosAfter &&
246          "Iterator should have position after successful advancement");
247   if (isAheadOfRange(State, *PosAfter)) {
248     auto *N = C.generateErrorNode(State);
249     if (!N)
250       return;
251     reportBug("Iterator decremented ahead of its valid range.", LHS,
252                         C, N);
253   }
254   if (isBehindPastTheEnd(State, *PosAfter)) {
255     auto *N = C.generateErrorNode(State);
256     if (!N)
257       return;
258     reportBug("Iterator incremented behind the past-the-end "
259                         "iterator.", LHS, C, N);
260   }
261 }
262 
verifyAdvance(CheckerContext & C,SVal LHS,SVal RHS) const263 void IteratorRangeChecker::verifyAdvance(CheckerContext &C, SVal LHS,
264                                          SVal RHS) const {
265   verifyRandomIncrOrDecr(C, OO_PlusEqual, LHS, RHS);
266 }
267 
verifyPrev(CheckerContext & C,SVal LHS,SVal RHS) const268 void IteratorRangeChecker::verifyPrev(CheckerContext &C, SVal LHS,
269                                       SVal RHS) const {
270   verifyRandomIncrOrDecr(C, OO_Minus, LHS, RHS);
271 }
272 
verifyNext(CheckerContext & C,SVal LHS,SVal RHS) const273 void IteratorRangeChecker::verifyNext(CheckerContext &C, SVal LHS,
274                                       SVal RHS) const {
275   verifyRandomIncrOrDecr(C, OO_Plus, LHS, RHS);
276 }
277 
reportBug(const StringRef & Message,SVal Val,CheckerContext & C,ExplodedNode * ErrNode) const278 void IteratorRangeChecker::reportBug(const StringRef &Message, SVal Val,
279                                      CheckerContext &C,
280                                      ExplodedNode *ErrNode) const {
281   auto R = std::make_unique<PathSensitiveBugReport>(*OutOfRangeBugType, Message,
282                                                     ErrNode);
283 
284   const auto *Pos = getIteratorPosition(C.getState(), Val);
285   assert(Pos && "Iterator without known position cannot be out-of-range.");
286 
287   R->markInteresting(Val);
288   R->markInteresting(Pos->getContainer());
289   C.emitReport(std::move(R));
290 }
291 
292 namespace {
293 
294 bool isLess(ProgramStateRef State, SymbolRef Sym1, SymbolRef Sym2);
295 bool isGreater(ProgramStateRef State, SymbolRef Sym1, SymbolRef Sym2);
296 bool isEqual(ProgramStateRef State, SymbolRef Sym1, SymbolRef Sym2);
297 
isZero(ProgramStateRef State,const NonLoc & Val)298 bool isZero(ProgramStateRef State, const NonLoc &Val) {
299   auto &BVF = State->getBasicVals();
300   return compare(State, Val,
301                  nonloc::ConcreteInt(BVF.getValue(llvm::APSInt::get(0))),
302                  BO_EQ);
303 }
304 
isPastTheEnd(ProgramStateRef State,const IteratorPosition & Pos)305 bool isPastTheEnd(ProgramStateRef State, const IteratorPosition &Pos) {
306   const auto *Cont = Pos.getContainer();
307   const auto *CData = getContainerData(State, Cont);
308   if (!CData)
309     return false;
310 
311   const auto End = CData->getEnd();
312   if (End) {
313     if (isEqual(State, Pos.getOffset(), End)) {
314       return true;
315     }
316   }
317 
318   return false;
319 }
320 
isAheadOfRange(ProgramStateRef State,const IteratorPosition & Pos)321 bool isAheadOfRange(ProgramStateRef State, const IteratorPosition &Pos) {
322   const auto *Cont = Pos.getContainer();
323   const auto *CData = getContainerData(State, Cont);
324   if (!CData)
325     return false;
326 
327   const auto Beg = CData->getBegin();
328   if (Beg) {
329     if (isLess(State, Pos.getOffset(), Beg)) {
330       return true;
331     }
332   }
333 
334   return false;
335 }
336 
isBehindPastTheEnd(ProgramStateRef State,const IteratorPosition & Pos)337 bool isBehindPastTheEnd(ProgramStateRef State, const IteratorPosition &Pos) {
338   const auto *Cont = Pos.getContainer();
339   const auto *CData = getContainerData(State, Cont);
340   if (!CData)
341     return false;
342 
343   const auto End = CData->getEnd();
344   if (End) {
345     if (isGreater(State, Pos.getOffset(), End)) {
346       return true;
347     }
348   }
349 
350   return false;
351 }
352 
isLess(ProgramStateRef State,SymbolRef Sym1,SymbolRef Sym2)353 bool isLess(ProgramStateRef State, SymbolRef Sym1, SymbolRef Sym2) {
354   return compare(State, Sym1, Sym2, BO_LT);
355 }
356 
isGreater(ProgramStateRef State,SymbolRef Sym1,SymbolRef Sym2)357 bool isGreater(ProgramStateRef State, SymbolRef Sym1, SymbolRef Sym2) {
358   return compare(State, Sym1, Sym2, BO_GT);
359 }
360 
isEqual(ProgramStateRef State,SymbolRef Sym1,SymbolRef Sym2)361 bool isEqual(ProgramStateRef State, SymbolRef Sym1, SymbolRef Sym2) {
362   return compare(State, Sym1, Sym2, BO_EQ);
363 }
364 
365 } // namespace
366 
registerIteratorRangeChecker(CheckerManager & mgr)367 void ento::registerIteratorRangeChecker(CheckerManager &mgr) {
368   mgr.registerChecker<IteratorRangeChecker>();
369 }
370 
shouldRegisterIteratorRangeChecker(const CheckerManager & mgr)371 bool ento::shouldRegisterIteratorRangeChecker(const CheckerManager &mgr) {
372   return true;
373 }
374