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1 // BugReporterVisitors.cpp - Helpers for reporting bugs -----------*- C++ -*--//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 //  This file defines a set of BugReporter "visitors" which can be used to
11 //  enhance the diagnostics reported for a bug.
12 //
13 //===----------------------------------------------------------------------===//
14 #include "clang/StaticAnalyzer/Core/BugReporter/BugReporterVisitor.h"
15 #include "clang/AST/Expr.h"
16 #include "clang/AST/ExprObjC.h"
17 #include "clang/Analysis/CFGStmtMap.h"
18 #include "clang/StaticAnalyzer/Core/BugReporter/BugReporter.h"
19 #include "clang/StaticAnalyzer/Core/BugReporter/PathDiagnostic.h"
20 #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
21 #include "clang/StaticAnalyzer/Core/PathSensitive/ExplodedGraph.h"
22 #include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
23 #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
24 #include "llvm/ADT/SmallString.h"
25 #include "llvm/ADT/StringExtras.h"
26 #include "llvm/Support/raw_ostream.h"
27 
28 using namespace clang;
29 using namespace ento;
30 
31 using llvm::FoldingSetNodeID;
32 
33 //===----------------------------------------------------------------------===//
34 // Utility functions.
35 //===----------------------------------------------------------------------===//
36 
isDeclRefExprToReference(const Expr * E)37 bool bugreporter::isDeclRefExprToReference(const Expr *E) {
38   if (const DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E)) {
39     return DRE->getDecl()->getType()->isReferenceType();
40   }
41   return false;
42 }
43 
getDerefExpr(const Stmt * S)44 const Expr *bugreporter::getDerefExpr(const Stmt *S) {
45   // Pattern match for a few useful cases:
46   //   a[0], p->f, *p
47   const Expr *E = dyn_cast<Expr>(S);
48   if (!E)
49     return nullptr;
50   E = E->IgnoreParenCasts();
51 
52   while (true) {
53     if (const BinaryOperator *B = dyn_cast<BinaryOperator>(E)) {
54       assert(B->isAssignmentOp());
55       E = B->getLHS()->IgnoreParenCasts();
56       continue;
57     }
58     else if (const UnaryOperator *U = dyn_cast<UnaryOperator>(E)) {
59       if (U->getOpcode() == UO_Deref)
60         return U->getSubExpr()->IgnoreParenCasts();
61     }
62     else if (const MemberExpr *ME = dyn_cast<MemberExpr>(E)) {
63       if (ME->isArrow() || isDeclRefExprToReference(ME->getBase())) {
64         return ME->getBase()->IgnoreParenCasts();
65       } else {
66         // If we have a member expr with a dot, the base must have been
67         // dereferenced.
68         return getDerefExpr(ME->getBase());
69       }
70     }
71     else if (const ObjCIvarRefExpr *IvarRef = dyn_cast<ObjCIvarRefExpr>(E)) {
72       return IvarRef->getBase()->IgnoreParenCasts();
73     }
74     else if (const ArraySubscriptExpr *AE = dyn_cast<ArraySubscriptExpr>(E)) {
75       return AE->getBase();
76     }
77     else if (isDeclRefExprToReference(E)) {
78       return E;
79     }
80     break;
81   }
82 
83   return nullptr;
84 }
85 
GetDenomExpr(const ExplodedNode * N)86 const Stmt *bugreporter::GetDenomExpr(const ExplodedNode *N) {
87   const Stmt *S = N->getLocationAs<PreStmt>()->getStmt();
88   if (const BinaryOperator *BE = dyn_cast<BinaryOperator>(S))
89     return BE->getRHS();
90   return nullptr;
91 }
92 
GetRetValExpr(const ExplodedNode * N)93 const Stmt *bugreporter::GetRetValExpr(const ExplodedNode *N) {
94   const Stmt *S = N->getLocationAs<PostStmt>()->getStmt();
95   if (const ReturnStmt *RS = dyn_cast<ReturnStmt>(S))
96     return RS->getRetValue();
97   return nullptr;
98 }
99 
100 //===----------------------------------------------------------------------===//
101 // Definitions for bug reporter visitors.
102 //===----------------------------------------------------------------------===//
103 
104 std::unique_ptr<PathDiagnosticPiece>
getEndPath(BugReporterContext & BRC,const ExplodedNode * EndPathNode,BugReport & BR)105 BugReporterVisitor::getEndPath(BugReporterContext &BRC,
106                                const ExplodedNode *EndPathNode, BugReport &BR) {
107   return nullptr;
108 }
109 
getDefaultEndPath(BugReporterContext & BRC,const ExplodedNode * EndPathNode,BugReport & BR)110 std::unique_ptr<PathDiagnosticPiece> BugReporterVisitor::getDefaultEndPath(
111     BugReporterContext &BRC, const ExplodedNode *EndPathNode, BugReport &BR) {
112   PathDiagnosticLocation L =
113     PathDiagnosticLocation::createEndOfPath(EndPathNode,BRC.getSourceManager());
114 
115   const auto &Ranges = BR.getRanges();
116 
117   // Only add the statement itself as a range if we didn't specify any
118   // special ranges for this report.
119   auto P = llvm::make_unique<PathDiagnosticEventPiece>(
120       L, BR.getDescription(), Ranges.begin() == Ranges.end());
121   for (SourceRange Range : Ranges)
122     P->addRange(Range);
123 
124   return std::move(P);
125 }
126 
127 
128 namespace {
129 /// Emits an extra note at the return statement of an interesting stack frame.
130 ///
131 /// The returned value is marked as an interesting value, and if it's null,
132 /// adds a visitor to track where it became null.
133 ///
134 /// This visitor is intended to be used when another visitor discovers that an
135 /// interesting value comes from an inlined function call.
136 class ReturnVisitor : public BugReporterVisitorImpl<ReturnVisitor> {
137   const StackFrameContext *StackFrame;
138   enum {
139     Initial,
140     MaybeUnsuppress,
141     Satisfied
142   } Mode;
143 
144   bool EnableNullFPSuppression;
145 
146 public:
ReturnVisitor(const StackFrameContext * Frame,bool Suppressed)147   ReturnVisitor(const StackFrameContext *Frame, bool Suppressed)
148     : StackFrame(Frame), Mode(Initial), EnableNullFPSuppression(Suppressed) {}
149 
getTag()150   static void *getTag() {
151     static int Tag = 0;
152     return static_cast<void *>(&Tag);
153   }
154 
Profile(llvm::FoldingSetNodeID & ID) const155   void Profile(llvm::FoldingSetNodeID &ID) const override {
156     ID.AddPointer(ReturnVisitor::getTag());
157     ID.AddPointer(StackFrame);
158     ID.AddBoolean(EnableNullFPSuppression);
159   }
160 
161   /// Adds a ReturnVisitor if the given statement represents a call that was
162   /// inlined.
163   ///
164   /// This will search back through the ExplodedGraph, starting from the given
165   /// node, looking for when the given statement was processed. If it turns out
166   /// the statement is a call that was inlined, we add the visitor to the
167   /// bug report, so it can print a note later.
addVisitorIfNecessary(const ExplodedNode * Node,const Stmt * S,BugReport & BR,bool InEnableNullFPSuppression)168   static void addVisitorIfNecessary(const ExplodedNode *Node, const Stmt *S,
169                                     BugReport &BR,
170                                     bool InEnableNullFPSuppression) {
171     if (!CallEvent::isCallStmt(S))
172       return;
173 
174     // First, find when we processed the statement.
175     do {
176       if (Optional<CallExitEnd> CEE = Node->getLocationAs<CallExitEnd>())
177         if (CEE->getCalleeContext()->getCallSite() == S)
178           break;
179       if (Optional<StmtPoint> SP = Node->getLocationAs<StmtPoint>())
180         if (SP->getStmt() == S)
181           break;
182 
183       Node = Node->getFirstPred();
184     } while (Node);
185 
186     // Next, step over any post-statement checks.
187     while (Node && Node->getLocation().getAs<PostStmt>())
188       Node = Node->getFirstPred();
189     if (!Node)
190       return;
191 
192     // Finally, see if we inlined the call.
193     Optional<CallExitEnd> CEE = Node->getLocationAs<CallExitEnd>();
194     if (!CEE)
195       return;
196 
197     const StackFrameContext *CalleeContext = CEE->getCalleeContext();
198     if (CalleeContext->getCallSite() != S)
199       return;
200 
201     // Check the return value.
202     ProgramStateRef State = Node->getState();
203     SVal RetVal = State->getSVal(S, Node->getLocationContext());
204 
205     // Handle cases where a reference is returned and then immediately used.
206     if (cast<Expr>(S)->isGLValue())
207       if (Optional<Loc> LValue = RetVal.getAs<Loc>())
208         RetVal = State->getSVal(*LValue);
209 
210     // See if the return value is NULL. If so, suppress the report.
211     SubEngine *Eng = State->getStateManager().getOwningEngine();
212     assert(Eng && "Cannot file a bug report without an owning engine");
213     AnalyzerOptions &Options = Eng->getAnalysisManager().options;
214 
215     bool EnableNullFPSuppression = false;
216     if (InEnableNullFPSuppression && Options.shouldSuppressNullReturnPaths())
217       if (Optional<Loc> RetLoc = RetVal.getAs<Loc>())
218         EnableNullFPSuppression = State->isNull(*RetLoc).isConstrainedTrue();
219 
220     BR.markInteresting(CalleeContext);
221     BR.addVisitor(llvm::make_unique<ReturnVisitor>(CalleeContext,
222                                                    EnableNullFPSuppression));
223   }
224 
225   /// Returns true if any counter-suppression heuristics are enabled for
226   /// ReturnVisitor.
hasCounterSuppression(AnalyzerOptions & Options)227   static bool hasCounterSuppression(AnalyzerOptions &Options) {
228     return Options.shouldAvoidSuppressingNullArgumentPaths();
229   }
230 
visitNodeInitial(const ExplodedNode * N,const ExplodedNode * PrevN,BugReporterContext & BRC,BugReport & BR)231   PathDiagnosticPiece *visitNodeInitial(const ExplodedNode *N,
232                                         const ExplodedNode *PrevN,
233                                         BugReporterContext &BRC,
234                                         BugReport &BR) {
235     // Only print a message at the interesting return statement.
236     if (N->getLocationContext() != StackFrame)
237       return nullptr;
238 
239     Optional<StmtPoint> SP = N->getLocationAs<StmtPoint>();
240     if (!SP)
241       return nullptr;
242 
243     const ReturnStmt *Ret = dyn_cast<ReturnStmt>(SP->getStmt());
244     if (!Ret)
245       return nullptr;
246 
247     // Okay, we're at the right return statement, but do we have the return
248     // value available?
249     ProgramStateRef State = N->getState();
250     SVal V = State->getSVal(Ret, StackFrame);
251     if (V.isUnknownOrUndef())
252       return nullptr;
253 
254     // Don't print any more notes after this one.
255     Mode = Satisfied;
256 
257     const Expr *RetE = Ret->getRetValue();
258     assert(RetE && "Tracking a return value for a void function");
259 
260     // Handle cases where a reference is returned and then immediately used.
261     Optional<Loc> LValue;
262     if (RetE->isGLValue()) {
263       if ((LValue = V.getAs<Loc>())) {
264         SVal RValue = State->getRawSVal(*LValue, RetE->getType());
265         if (RValue.getAs<DefinedSVal>())
266           V = RValue;
267       }
268     }
269 
270     // Ignore aggregate rvalues.
271     if (V.getAs<nonloc::LazyCompoundVal>() ||
272         V.getAs<nonloc::CompoundVal>())
273       return nullptr;
274 
275     RetE = RetE->IgnoreParenCasts();
276 
277     // If we can't prove the return value is 0, just mark it interesting, and
278     // make sure to track it into any further inner functions.
279     if (!State->isNull(V).isConstrainedTrue()) {
280       BR.markInteresting(V);
281       ReturnVisitor::addVisitorIfNecessary(N, RetE, BR,
282                                            EnableNullFPSuppression);
283       return nullptr;
284     }
285 
286     // If we're returning 0, we should track where that 0 came from.
287     bugreporter::trackNullOrUndefValue(N, RetE, BR, /*IsArg*/ false,
288                                        EnableNullFPSuppression);
289 
290     // Build an appropriate message based on the return value.
291     SmallString<64> Msg;
292     llvm::raw_svector_ostream Out(Msg);
293 
294     if (V.getAs<Loc>()) {
295       // If we have counter-suppression enabled, make sure we keep visiting
296       // future nodes. We want to emit a path note as well, in case
297       // the report is resurrected as valid later on.
298       ExprEngine &Eng = BRC.getBugReporter().getEngine();
299       AnalyzerOptions &Options = Eng.getAnalysisManager().options;
300       if (EnableNullFPSuppression && hasCounterSuppression(Options))
301         Mode = MaybeUnsuppress;
302 
303       if (RetE->getType()->isObjCObjectPointerType())
304         Out << "Returning nil";
305       else
306         Out << "Returning null pointer";
307     } else {
308       Out << "Returning zero";
309     }
310 
311     if (LValue) {
312       if (const MemRegion *MR = LValue->getAsRegion()) {
313         if (MR->canPrintPretty()) {
314           Out << " (reference to ";
315           MR->printPretty(Out);
316           Out << ")";
317         }
318       }
319     } else {
320       // FIXME: We should have a more generalized location printing mechanism.
321       if (const DeclRefExpr *DR = dyn_cast<DeclRefExpr>(RetE))
322         if (const DeclaratorDecl *DD = dyn_cast<DeclaratorDecl>(DR->getDecl()))
323           Out << " (loaded from '" << *DD << "')";
324     }
325 
326     PathDiagnosticLocation L(Ret, BRC.getSourceManager(), StackFrame);
327     if (!L.isValid() || !L.asLocation().isValid())
328       return nullptr;
329 
330     return new PathDiagnosticEventPiece(L, Out.str());
331   }
332 
visitNodeMaybeUnsuppress(const ExplodedNode * N,const ExplodedNode * PrevN,BugReporterContext & BRC,BugReport & BR)333   PathDiagnosticPiece *visitNodeMaybeUnsuppress(const ExplodedNode *N,
334                                                 const ExplodedNode *PrevN,
335                                                 BugReporterContext &BRC,
336                                                 BugReport &BR) {
337 #ifndef NDEBUG
338     ExprEngine &Eng = BRC.getBugReporter().getEngine();
339     AnalyzerOptions &Options = Eng.getAnalysisManager().options;
340     assert(hasCounterSuppression(Options));
341 #endif
342 
343     // Are we at the entry node for this call?
344     Optional<CallEnter> CE = N->getLocationAs<CallEnter>();
345     if (!CE)
346       return nullptr;
347 
348     if (CE->getCalleeContext() != StackFrame)
349       return nullptr;
350 
351     Mode = Satisfied;
352 
353     // Don't automatically suppress a report if one of the arguments is
354     // known to be a null pointer. Instead, start tracking /that/ null
355     // value back to its origin.
356     ProgramStateManager &StateMgr = BRC.getStateManager();
357     CallEventManager &CallMgr = StateMgr.getCallEventManager();
358 
359     ProgramStateRef State = N->getState();
360     CallEventRef<> Call = CallMgr.getCaller(StackFrame, State);
361     for (unsigned I = 0, E = Call->getNumArgs(); I != E; ++I) {
362       Optional<Loc> ArgV = Call->getArgSVal(I).getAs<Loc>();
363       if (!ArgV)
364         continue;
365 
366       const Expr *ArgE = Call->getArgExpr(I);
367       if (!ArgE)
368         continue;
369 
370       // Is it possible for this argument to be non-null?
371       if (!State->isNull(*ArgV).isConstrainedTrue())
372         continue;
373 
374       if (bugreporter::trackNullOrUndefValue(N, ArgE, BR, /*IsArg=*/true,
375                                              EnableNullFPSuppression))
376         BR.removeInvalidation(ReturnVisitor::getTag(), StackFrame);
377 
378       // If we /can't/ track the null pointer, we should err on the side of
379       // false negatives, and continue towards marking this report invalid.
380       // (We will still look at the other arguments, though.)
381     }
382 
383     return nullptr;
384   }
385 
VisitNode(const ExplodedNode * N,const ExplodedNode * PrevN,BugReporterContext & BRC,BugReport & BR)386   PathDiagnosticPiece *VisitNode(const ExplodedNode *N,
387                                  const ExplodedNode *PrevN,
388                                  BugReporterContext &BRC,
389                                  BugReport &BR) override {
390     switch (Mode) {
391     case Initial:
392       return visitNodeInitial(N, PrevN, BRC, BR);
393     case MaybeUnsuppress:
394       return visitNodeMaybeUnsuppress(N, PrevN, BRC, BR);
395     case Satisfied:
396       return nullptr;
397     }
398 
399     llvm_unreachable("Invalid visit mode!");
400   }
401 
getEndPath(BugReporterContext & BRC,const ExplodedNode * N,BugReport & BR)402   std::unique_ptr<PathDiagnosticPiece> getEndPath(BugReporterContext &BRC,
403                                                   const ExplodedNode *N,
404                                                   BugReport &BR) override {
405     if (EnableNullFPSuppression)
406       BR.markInvalid(ReturnVisitor::getTag(), StackFrame);
407     return nullptr;
408   }
409 };
410 } // end anonymous namespace
411 
412 
Profile(llvm::FoldingSetNodeID & ID) const413 void FindLastStoreBRVisitor ::Profile(llvm::FoldingSetNodeID &ID) const {
414   static int tag = 0;
415   ID.AddPointer(&tag);
416   ID.AddPointer(R);
417   ID.Add(V);
418   ID.AddBoolean(EnableNullFPSuppression);
419 }
420 
421 /// Returns true if \p N represents the DeclStmt declaring and initializing
422 /// \p VR.
isInitializationOfVar(const ExplodedNode * N,const VarRegion * VR)423 static bool isInitializationOfVar(const ExplodedNode *N, const VarRegion *VR) {
424   Optional<PostStmt> P = N->getLocationAs<PostStmt>();
425   if (!P)
426     return false;
427 
428   const DeclStmt *DS = P->getStmtAs<DeclStmt>();
429   if (!DS)
430     return false;
431 
432   if (DS->getSingleDecl() != VR->getDecl())
433     return false;
434 
435   const MemSpaceRegion *VarSpace = VR->getMemorySpace();
436   const StackSpaceRegion *FrameSpace = dyn_cast<StackSpaceRegion>(VarSpace);
437   if (!FrameSpace) {
438     // If we ever directly evaluate global DeclStmts, this assertion will be
439     // invalid, but this still seems preferable to silently accepting an
440     // initialization that may be for a path-sensitive variable.
441     assert(VR->getDecl()->isStaticLocal() && "non-static stackless VarRegion");
442     return true;
443   }
444 
445   assert(VR->getDecl()->hasLocalStorage());
446   const LocationContext *LCtx = N->getLocationContext();
447   return FrameSpace->getStackFrame() == LCtx->getCurrentStackFrame();
448 }
449 
VisitNode(const ExplodedNode * Succ,const ExplodedNode * Pred,BugReporterContext & BRC,BugReport & BR)450 PathDiagnosticPiece *FindLastStoreBRVisitor::VisitNode(const ExplodedNode *Succ,
451                                                        const ExplodedNode *Pred,
452                                                        BugReporterContext &BRC,
453                                                        BugReport &BR) {
454 
455   if (Satisfied)
456     return nullptr;
457 
458   const ExplodedNode *StoreSite = nullptr;
459   const Expr *InitE = nullptr;
460   bool IsParam = false;
461 
462   // First see if we reached the declaration of the region.
463   if (const VarRegion *VR = dyn_cast<VarRegion>(R)) {
464     if (isInitializationOfVar(Pred, VR)) {
465       StoreSite = Pred;
466       InitE = VR->getDecl()->getInit();
467     }
468   }
469 
470   // If this is a post initializer expression, initializing the region, we
471   // should track the initializer expression.
472   if (Optional<PostInitializer> PIP = Pred->getLocationAs<PostInitializer>()) {
473     const MemRegion *FieldReg = (const MemRegion *)PIP->getLocationValue();
474     if (FieldReg && FieldReg == R) {
475       StoreSite = Pred;
476       InitE = PIP->getInitializer()->getInit();
477     }
478   }
479 
480   // Otherwise, see if this is the store site:
481   // (1) Succ has this binding and Pred does not, i.e. this is
482   //     where the binding first occurred.
483   // (2) Succ has this binding and is a PostStore node for this region, i.e.
484   //     the same binding was re-assigned here.
485   if (!StoreSite) {
486     if (Succ->getState()->getSVal(R) != V)
487       return nullptr;
488 
489     if (Pred->getState()->getSVal(R) == V) {
490       Optional<PostStore> PS = Succ->getLocationAs<PostStore>();
491       if (!PS || PS->getLocationValue() != R)
492         return nullptr;
493     }
494 
495     StoreSite = Succ;
496 
497     // If this is an assignment expression, we can track the value
498     // being assigned.
499     if (Optional<PostStmt> P = Succ->getLocationAs<PostStmt>())
500       if (const BinaryOperator *BO = P->getStmtAs<BinaryOperator>())
501         if (BO->isAssignmentOp())
502           InitE = BO->getRHS();
503 
504     // If this is a call entry, the variable should be a parameter.
505     // FIXME: Handle CXXThisRegion as well. (This is not a priority because
506     // 'this' should never be NULL, but this visitor isn't just for NULL and
507     // UndefinedVal.)
508     if (Optional<CallEnter> CE = Succ->getLocationAs<CallEnter>()) {
509       if (const VarRegion *VR = dyn_cast<VarRegion>(R)) {
510         const ParmVarDecl *Param = cast<ParmVarDecl>(VR->getDecl());
511 
512         ProgramStateManager &StateMgr = BRC.getStateManager();
513         CallEventManager &CallMgr = StateMgr.getCallEventManager();
514 
515         CallEventRef<> Call = CallMgr.getCaller(CE->getCalleeContext(),
516                                                 Succ->getState());
517         InitE = Call->getArgExpr(Param->getFunctionScopeIndex());
518         IsParam = true;
519       }
520     }
521 
522     // If this is a CXXTempObjectRegion, the Expr responsible for its creation
523     // is wrapped inside of it.
524     if (const CXXTempObjectRegion *TmpR = dyn_cast<CXXTempObjectRegion>(R))
525       InitE = TmpR->getExpr();
526   }
527 
528   if (!StoreSite)
529     return nullptr;
530   Satisfied = true;
531 
532   // If we have an expression that provided the value, try to track where it
533   // came from.
534   if (InitE) {
535     if (V.isUndef() ||
536         V.getAs<loc::ConcreteInt>() || V.getAs<nonloc::ConcreteInt>()) {
537       if (!IsParam)
538         InitE = InitE->IgnoreParenCasts();
539       bugreporter::trackNullOrUndefValue(StoreSite, InitE, BR, IsParam,
540                                          EnableNullFPSuppression);
541     } else {
542       ReturnVisitor::addVisitorIfNecessary(StoreSite, InitE->IgnoreParenCasts(),
543                                            BR, EnableNullFPSuppression);
544     }
545   }
546 
547   // Okay, we've found the binding. Emit an appropriate message.
548   SmallString<256> sbuf;
549   llvm::raw_svector_ostream os(sbuf);
550 
551   if (Optional<PostStmt> PS = StoreSite->getLocationAs<PostStmt>()) {
552     const Stmt *S = PS->getStmt();
553     const char *action = nullptr;
554     const DeclStmt *DS = dyn_cast<DeclStmt>(S);
555     const VarRegion *VR = dyn_cast<VarRegion>(R);
556 
557     if (DS) {
558       action = R->canPrintPretty() ? "initialized to " :
559                                      "Initializing to ";
560     } else if (isa<BlockExpr>(S)) {
561       action = R->canPrintPretty() ? "captured by block as " :
562                                      "Captured by block as ";
563       if (VR) {
564         // See if we can get the BlockVarRegion.
565         ProgramStateRef State = StoreSite->getState();
566         SVal V = State->getSVal(S, PS->getLocationContext());
567         if (const BlockDataRegion *BDR =
568               dyn_cast_or_null<BlockDataRegion>(V.getAsRegion())) {
569           if (const VarRegion *OriginalR = BDR->getOriginalRegion(VR)) {
570             if (Optional<KnownSVal> KV =
571                 State->getSVal(OriginalR).getAs<KnownSVal>())
572               BR.addVisitor(llvm::make_unique<FindLastStoreBRVisitor>(
573                   *KV, OriginalR, EnableNullFPSuppression));
574           }
575         }
576       }
577     }
578 
579     if (action) {
580       if (R->canPrintPretty()) {
581         R->printPretty(os);
582         os << " ";
583       }
584 
585       if (V.getAs<loc::ConcreteInt>()) {
586         bool b = false;
587         if (R->isBoundable()) {
588           if (const TypedValueRegion *TR = dyn_cast<TypedValueRegion>(R)) {
589             if (TR->getValueType()->isObjCObjectPointerType()) {
590               os << action << "nil";
591               b = true;
592             }
593           }
594         }
595 
596         if (!b)
597           os << action << "a null pointer value";
598       } else if (Optional<nonloc::ConcreteInt> CVal =
599                      V.getAs<nonloc::ConcreteInt>()) {
600         os << action << CVal->getValue();
601       }
602       else if (DS) {
603         if (V.isUndef()) {
604           if (isa<VarRegion>(R)) {
605             const VarDecl *VD = cast<VarDecl>(DS->getSingleDecl());
606             if (VD->getInit()) {
607               os << (R->canPrintPretty() ? "initialized" : "Initializing")
608                  << " to a garbage value";
609             } else {
610               os << (R->canPrintPretty() ? "declared" : "Declaring")
611                  << " without an initial value";
612             }
613           }
614         }
615         else {
616           os << (R->canPrintPretty() ? "initialized" : "Initialized")
617              << " here";
618         }
619       }
620     }
621   } else if (StoreSite->getLocation().getAs<CallEnter>()) {
622     if (const VarRegion *VR = dyn_cast<VarRegion>(R)) {
623       const ParmVarDecl *Param = cast<ParmVarDecl>(VR->getDecl());
624 
625       os << "Passing ";
626 
627       if (V.getAs<loc::ConcreteInt>()) {
628         if (Param->getType()->isObjCObjectPointerType())
629           os << "nil object reference";
630         else
631           os << "null pointer value";
632       } else if (V.isUndef()) {
633         os << "uninitialized value";
634       } else if (Optional<nonloc::ConcreteInt> CI =
635                      V.getAs<nonloc::ConcreteInt>()) {
636         os << "the value " << CI->getValue();
637       } else {
638         os << "value";
639       }
640 
641       // Printed parameter indexes are 1-based, not 0-based.
642       unsigned Idx = Param->getFunctionScopeIndex() + 1;
643       os << " via " << Idx << llvm::getOrdinalSuffix(Idx) << " parameter";
644       if (R->canPrintPretty()) {
645         os << " ";
646         R->printPretty(os);
647       }
648     }
649   }
650 
651   if (os.str().empty()) {
652     if (V.getAs<loc::ConcreteInt>()) {
653       bool b = false;
654       if (R->isBoundable()) {
655         if (const TypedValueRegion *TR = dyn_cast<TypedValueRegion>(R)) {
656           if (TR->getValueType()->isObjCObjectPointerType()) {
657             os << "nil object reference stored";
658             b = true;
659           }
660         }
661       }
662       if (!b) {
663         if (R->canPrintPretty())
664           os << "Null pointer value stored";
665         else
666           os << "Storing null pointer value";
667       }
668 
669     } else if (V.isUndef()) {
670       if (R->canPrintPretty())
671         os << "Uninitialized value stored";
672       else
673         os << "Storing uninitialized value";
674 
675     } else if (Optional<nonloc::ConcreteInt> CV =
676                    V.getAs<nonloc::ConcreteInt>()) {
677       if (R->canPrintPretty())
678         os << "The value " << CV->getValue() << " is assigned";
679       else
680         os << "Assigning " << CV->getValue();
681 
682     } else {
683       if (R->canPrintPretty())
684         os << "Value assigned";
685       else
686         os << "Assigning value";
687     }
688 
689     if (R->canPrintPretty()) {
690       os << " to ";
691       R->printPretty(os);
692     }
693   }
694 
695   // Construct a new PathDiagnosticPiece.
696   ProgramPoint P = StoreSite->getLocation();
697   PathDiagnosticLocation L;
698   if (P.getAs<CallEnter>() && InitE)
699     L = PathDiagnosticLocation(InitE, BRC.getSourceManager(),
700                                P.getLocationContext());
701 
702   if (!L.isValid() || !L.asLocation().isValid())
703     L = PathDiagnosticLocation::create(P, BRC.getSourceManager());
704 
705   if (!L.isValid() || !L.asLocation().isValid())
706     return nullptr;
707 
708   return new PathDiagnosticEventPiece(L, os.str());
709 }
710 
Profile(llvm::FoldingSetNodeID & ID) const711 void TrackConstraintBRVisitor::Profile(llvm::FoldingSetNodeID &ID) const {
712   static int tag = 0;
713   ID.AddPointer(&tag);
714   ID.AddBoolean(Assumption);
715   ID.Add(Constraint);
716 }
717 
718 /// Return the tag associated with this visitor.  This tag will be used
719 /// to make all PathDiagnosticPieces created by this visitor.
getTag()720 const char *TrackConstraintBRVisitor::getTag() {
721   return "TrackConstraintBRVisitor";
722 }
723 
isUnderconstrained(const ExplodedNode * N) const724 bool TrackConstraintBRVisitor::isUnderconstrained(const ExplodedNode *N) const {
725   if (IsZeroCheck)
726     return N->getState()->isNull(Constraint).isUnderconstrained();
727   return (bool)N->getState()->assume(Constraint, !Assumption);
728 }
729 
730 PathDiagnosticPiece *
VisitNode(const ExplodedNode * N,const ExplodedNode * PrevN,BugReporterContext & BRC,BugReport & BR)731 TrackConstraintBRVisitor::VisitNode(const ExplodedNode *N,
732                                     const ExplodedNode *PrevN,
733                                     BugReporterContext &BRC,
734                                     BugReport &BR) {
735   if (IsSatisfied)
736     return nullptr;
737 
738   // Start tracking after we see the first state in which the value is
739   // constrained.
740   if (!IsTrackingTurnedOn)
741     if (!isUnderconstrained(N))
742       IsTrackingTurnedOn = true;
743   if (!IsTrackingTurnedOn)
744     return nullptr;
745 
746   // Check if in the previous state it was feasible for this constraint
747   // to *not* be true.
748   if (isUnderconstrained(PrevN)) {
749 
750     IsSatisfied = true;
751 
752     // As a sanity check, make sure that the negation of the constraint
753     // was infeasible in the current state.  If it is feasible, we somehow
754     // missed the transition point.
755     assert(!isUnderconstrained(N));
756 
757     // We found the transition point for the constraint.  We now need to
758     // pretty-print the constraint. (work-in-progress)
759     SmallString<64> sbuf;
760     llvm::raw_svector_ostream os(sbuf);
761 
762     if (Constraint.getAs<Loc>()) {
763       os << "Assuming pointer value is ";
764       os << (Assumption ? "non-null" : "null");
765     }
766 
767     if (os.str().empty())
768       return nullptr;
769 
770     // Construct a new PathDiagnosticPiece.
771     ProgramPoint P = N->getLocation();
772     PathDiagnosticLocation L =
773       PathDiagnosticLocation::create(P, BRC.getSourceManager());
774     if (!L.isValid())
775       return nullptr;
776 
777     PathDiagnosticEventPiece *X = new PathDiagnosticEventPiece(L, os.str());
778     X->setTag(getTag());
779     return X;
780   }
781 
782   return nullptr;
783 }
784 
785 SuppressInlineDefensiveChecksVisitor::
SuppressInlineDefensiveChecksVisitor(DefinedSVal Value,const ExplodedNode * N)786 SuppressInlineDefensiveChecksVisitor(DefinedSVal Value, const ExplodedNode *N)
787   : V(Value), IsSatisfied(false), IsTrackingTurnedOn(false) {
788 
789     // Check if the visitor is disabled.
790     SubEngine *Eng = N->getState()->getStateManager().getOwningEngine();
791     assert(Eng && "Cannot file a bug report without an owning engine");
792     AnalyzerOptions &Options = Eng->getAnalysisManager().options;
793     if (!Options.shouldSuppressInlinedDefensiveChecks())
794       IsSatisfied = true;
795 
796     assert(N->getState()->isNull(V).isConstrainedTrue() &&
797            "The visitor only tracks the cases where V is constrained to 0");
798 }
799 
Profile(FoldingSetNodeID & ID) const800 void SuppressInlineDefensiveChecksVisitor::Profile(FoldingSetNodeID &ID) const {
801   static int id = 0;
802   ID.AddPointer(&id);
803   ID.Add(V);
804 }
805 
getTag()806 const char *SuppressInlineDefensiveChecksVisitor::getTag() {
807   return "IDCVisitor";
808 }
809 
810 PathDiagnosticPiece *
VisitNode(const ExplodedNode * Succ,const ExplodedNode * Pred,BugReporterContext & BRC,BugReport & BR)811 SuppressInlineDefensiveChecksVisitor::VisitNode(const ExplodedNode *Succ,
812                                                 const ExplodedNode *Pred,
813                                                 BugReporterContext &BRC,
814                                                 BugReport &BR) {
815   if (IsSatisfied)
816     return nullptr;
817 
818   // Start tracking after we see the first state in which the value is null.
819   if (!IsTrackingTurnedOn)
820     if (Succ->getState()->isNull(V).isConstrainedTrue())
821       IsTrackingTurnedOn = true;
822   if (!IsTrackingTurnedOn)
823     return nullptr;
824 
825   // Check if in the previous state it was feasible for this value
826   // to *not* be null.
827   if (!Pred->getState()->isNull(V).isConstrainedTrue()) {
828     IsSatisfied = true;
829 
830     assert(Succ->getState()->isNull(V).isConstrainedTrue());
831 
832     // Check if this is inlined defensive checks.
833     const LocationContext *CurLC =Succ->getLocationContext();
834     const LocationContext *ReportLC = BR.getErrorNode()->getLocationContext();
835     if (CurLC != ReportLC && !CurLC->isParentOf(ReportLC)) {
836       BR.markInvalid("Suppress IDC", CurLC);
837       return nullptr;
838     }
839 
840     // Treat defensive checks in function-like macros as if they were an inlined
841     // defensive check. If the bug location is not in a macro and the
842     // terminator for the current location is in a macro then suppress the
843     // warning.
844     auto BugPoint = BR.getErrorNode()->getLocation().getAs<StmtPoint>();
845 
846     if (!BugPoint)
847       return nullptr;
848 
849     SourceLocation BugLoc = BugPoint->getStmt()->getLocStart();
850     if (BugLoc.isMacroID())
851       return nullptr;
852 
853     ProgramPoint CurPoint = Succ->getLocation();
854     const Stmt *CurTerminatorStmt = nullptr;
855     if (auto BE = CurPoint.getAs<BlockEdge>()) {
856       CurTerminatorStmt = BE->getSrc()->getTerminator().getStmt();
857     } else if (auto SP = CurPoint.getAs<StmtPoint>()) {
858       const Stmt *CurStmt = SP->getStmt();
859       if (!CurStmt->getLocStart().isMacroID())
860         return nullptr;
861 
862       CFGStmtMap *Map = CurLC->getAnalysisDeclContext()->getCFGStmtMap();
863       CurTerminatorStmt = Map->getBlock(CurStmt)->getTerminator();
864     } else {
865       return nullptr;
866     }
867 
868     if (!CurTerminatorStmt)
869       return nullptr;
870 
871     SourceLocation TerminatorLoc = CurTerminatorStmt->getLocStart();
872     if (TerminatorLoc.isMacroID()) {
873       const SourceManager &SMgr = BRC.getSourceManager();
874       std::pair<FileID, unsigned> TLInfo = SMgr.getDecomposedLoc(TerminatorLoc);
875       SrcMgr::SLocEntry SE = SMgr.getSLocEntry(TLInfo.first);
876       const SrcMgr::ExpansionInfo &EInfo = SE.getExpansion();
877       if (EInfo.isFunctionMacroExpansion()) {
878         BR.markInvalid("Suppress Macro IDC", CurLC);
879         return nullptr;
880       }
881     }
882   }
883   return nullptr;
884 }
885 
getLocationRegionIfReference(const Expr * E,const ExplodedNode * N)886 static const MemRegion *getLocationRegionIfReference(const Expr *E,
887                                                      const ExplodedNode *N) {
888   if (const DeclRefExpr *DR = dyn_cast<DeclRefExpr>(E)) {
889     if (const VarDecl *VD = dyn_cast<VarDecl>(DR->getDecl())) {
890       if (!VD->getType()->isReferenceType())
891         return nullptr;
892       ProgramStateManager &StateMgr = N->getState()->getStateManager();
893       MemRegionManager &MRMgr = StateMgr.getRegionManager();
894       return MRMgr.getVarRegion(VD, N->getLocationContext());
895     }
896   }
897 
898   // FIXME: This does not handle other kinds of null references,
899   // for example, references from FieldRegions:
900   //   struct Wrapper { int &ref; };
901   //   Wrapper w = { *(int *)0 };
902   //   w.ref = 1;
903 
904   return nullptr;
905 }
906 
peelOffOuterExpr(const Expr * Ex,const ExplodedNode * N)907 static const Expr *peelOffOuterExpr(const Expr *Ex,
908                                     const ExplodedNode *N) {
909   Ex = Ex->IgnoreParenCasts();
910   if (const ExprWithCleanups *EWC = dyn_cast<ExprWithCleanups>(Ex))
911     return peelOffOuterExpr(EWC->getSubExpr(), N);
912   if (const OpaqueValueExpr *OVE = dyn_cast<OpaqueValueExpr>(Ex))
913     return peelOffOuterExpr(OVE->getSourceExpr(), N);
914   if (auto *POE = dyn_cast<PseudoObjectExpr>(Ex)) {
915     auto *PropRef = dyn_cast<ObjCPropertyRefExpr>(POE->getSyntacticForm());
916     if (PropRef && PropRef->isMessagingGetter()) {
917       const Expr *GetterMessageSend =
918           POE->getSemanticExpr(POE->getNumSemanticExprs() - 1);
919       assert(isa<ObjCMessageExpr>(GetterMessageSend));
920       return peelOffOuterExpr(GetterMessageSend, N);
921     }
922   }
923 
924   // Peel off the ternary operator.
925   if (const ConditionalOperator *CO = dyn_cast<ConditionalOperator>(Ex)) {
926     // Find a node where the branching occurred and find out which branch
927     // we took (true/false) by looking at the ExplodedGraph.
928     const ExplodedNode *NI = N;
929     do {
930       ProgramPoint ProgPoint = NI->getLocation();
931       if (Optional<BlockEdge> BE = ProgPoint.getAs<BlockEdge>()) {
932         const CFGBlock *srcBlk = BE->getSrc();
933         if (const Stmt *term = srcBlk->getTerminator()) {
934           if (term == CO) {
935             bool TookTrueBranch = (*(srcBlk->succ_begin()) == BE->getDst());
936             if (TookTrueBranch)
937               return peelOffOuterExpr(CO->getTrueExpr(), N);
938             else
939               return peelOffOuterExpr(CO->getFalseExpr(), N);
940           }
941         }
942       }
943       NI = NI->getFirstPred();
944     } while (NI);
945   }
946   return Ex;
947 }
948 
trackNullOrUndefValue(const ExplodedNode * N,const Stmt * S,BugReport & report,bool IsArg,bool EnableNullFPSuppression)949 bool bugreporter::trackNullOrUndefValue(const ExplodedNode *N,
950                                         const Stmt *S,
951                                         BugReport &report, bool IsArg,
952                                         bool EnableNullFPSuppression) {
953   if (!S || !N)
954     return false;
955 
956   if (const Expr *Ex = dyn_cast<Expr>(S)) {
957     Ex = Ex->IgnoreParenCasts();
958     const Expr *PeeledEx = peelOffOuterExpr(Ex, N);
959     if (Ex != PeeledEx)
960       S = PeeledEx;
961   }
962 
963   const Expr *Inner = nullptr;
964   if (const Expr *Ex = dyn_cast<Expr>(S)) {
965     Ex = Ex->IgnoreParenCasts();
966     if (ExplodedGraph::isInterestingLValueExpr(Ex) || CallEvent::isCallStmt(Ex))
967       Inner = Ex;
968   }
969 
970   if (IsArg && !Inner) {
971     assert(N->getLocation().getAs<CallEnter>() && "Tracking arg but not at call");
972   } else {
973     // Walk through nodes until we get one that matches the statement exactly.
974     // Alternately, if we hit a known lvalue for the statement, we know we've
975     // gone too far (though we can likely track the lvalue better anyway).
976     do {
977       const ProgramPoint &pp = N->getLocation();
978       if (Optional<StmtPoint> ps = pp.getAs<StmtPoint>()) {
979         if (ps->getStmt() == S || ps->getStmt() == Inner)
980           break;
981       } else if (Optional<CallExitEnd> CEE = pp.getAs<CallExitEnd>()) {
982         if (CEE->getCalleeContext()->getCallSite() == S ||
983             CEE->getCalleeContext()->getCallSite() == Inner)
984           break;
985       }
986       N = N->getFirstPred();
987     } while (N);
988 
989     if (!N)
990       return false;
991   }
992 
993   ProgramStateRef state = N->getState();
994 
995   // The message send could be nil due to the receiver being nil.
996   // At this point in the path, the receiver should be live since we are at the
997   // message send expr. If it is nil, start tracking it.
998   if (const Expr *Receiver = NilReceiverBRVisitor::getNilReceiver(S, N))
999     trackNullOrUndefValue(N, Receiver, report, false, EnableNullFPSuppression);
1000 
1001 
1002   // See if the expression we're interested refers to a variable.
1003   // If so, we can track both its contents and constraints on its value.
1004   if (Inner && ExplodedGraph::isInterestingLValueExpr(Inner)) {
1005     const MemRegion *R = nullptr;
1006 
1007     // Find the ExplodedNode where the lvalue (the value of 'Ex')
1008     // was computed.  We need this for getting the location value.
1009     const ExplodedNode *LVNode = N;
1010     while (LVNode) {
1011       if (Optional<PostStmt> P = LVNode->getLocation().getAs<PostStmt>()) {
1012         if (P->getStmt() == Inner)
1013           break;
1014       }
1015       LVNode = LVNode->getFirstPred();
1016     }
1017     assert(LVNode && "Unable to find the lvalue node.");
1018     ProgramStateRef LVState = LVNode->getState();
1019     SVal LVal = LVState->getSVal(Inner, LVNode->getLocationContext());
1020 
1021     if (LVState->isNull(LVal).isConstrainedTrue()) {
1022       // In case of C++ references, we want to differentiate between a null
1023       // reference and reference to null pointer.
1024       // If the LVal is null, check if we are dealing with null reference.
1025       // For those, we want to track the location of the reference.
1026       if (const MemRegion *RR = getLocationRegionIfReference(Inner, N))
1027         R = RR;
1028     } else {
1029       R = LVState->getSVal(Inner, LVNode->getLocationContext()).getAsRegion();
1030 
1031       // If this is a C++ reference to a null pointer, we are tracking the
1032       // pointer. In additon, we should find the store at which the reference
1033       // got initialized.
1034       if (const MemRegion *RR = getLocationRegionIfReference(Inner, N)) {
1035         if (Optional<KnownSVal> KV = LVal.getAs<KnownSVal>())
1036           report.addVisitor(llvm::make_unique<FindLastStoreBRVisitor>(
1037               *KV, RR, EnableNullFPSuppression));
1038       }
1039     }
1040 
1041     if (R) {
1042       // Mark both the variable region and its contents as interesting.
1043       SVal V = LVState->getRawSVal(loc::MemRegionVal(R));
1044 
1045       report.markInteresting(R);
1046       report.markInteresting(V);
1047       report.addVisitor(llvm::make_unique<UndefOrNullArgVisitor>(R));
1048 
1049       // If the contents are symbolic, find out when they became null.
1050       if (V.getAsLocSymbol(/*IncludeBaseRegions*/ true))
1051         report.addVisitor(llvm::make_unique<TrackConstraintBRVisitor>(
1052             V.castAs<DefinedSVal>(), false));
1053 
1054       // Add visitor, which will suppress inline defensive checks.
1055       if (Optional<DefinedSVal> DV = V.getAs<DefinedSVal>()) {
1056         if (!DV->isZeroConstant() && LVState->isNull(*DV).isConstrainedTrue() &&
1057             EnableNullFPSuppression) {
1058           report.addVisitor(
1059               llvm::make_unique<SuppressInlineDefensiveChecksVisitor>(*DV,
1060                                                                       LVNode));
1061         }
1062       }
1063 
1064       if (Optional<KnownSVal> KV = V.getAs<KnownSVal>())
1065         report.addVisitor(llvm::make_unique<FindLastStoreBRVisitor>(
1066             *KV, R, EnableNullFPSuppression));
1067       return true;
1068     }
1069   }
1070 
1071   // If the expression is not an "lvalue expression", we can still
1072   // track the constraints on its contents.
1073   SVal V = state->getSValAsScalarOrLoc(S, N->getLocationContext());
1074 
1075   // If the value came from an inlined function call, we should at least make
1076   // sure that function isn't pruned in our output.
1077   if (const Expr *E = dyn_cast<Expr>(S))
1078     S = E->IgnoreParenCasts();
1079 
1080   ReturnVisitor::addVisitorIfNecessary(N, S, report, EnableNullFPSuppression);
1081 
1082   // Uncomment this to find cases where we aren't properly getting the
1083   // base value that was dereferenced.
1084   // assert(!V.isUnknownOrUndef());
1085   // Is it a symbolic value?
1086   if (Optional<loc::MemRegionVal> L = V.getAs<loc::MemRegionVal>()) {
1087     // At this point we are dealing with the region's LValue.
1088     // However, if the rvalue is a symbolic region, we should track it as well.
1089     // Try to use the correct type when looking up the value.
1090     SVal RVal;
1091     if (const Expr *E = dyn_cast<Expr>(S))
1092       RVal = state->getRawSVal(L.getValue(), E->getType());
1093     else
1094       RVal = state->getSVal(L->getRegion());
1095 
1096     const MemRegion *RegionRVal = RVal.getAsRegion();
1097     report.addVisitor(llvm::make_unique<UndefOrNullArgVisitor>(L->getRegion()));
1098 
1099     if (RegionRVal && isa<SymbolicRegion>(RegionRVal)) {
1100       report.markInteresting(RegionRVal);
1101       report.addVisitor(llvm::make_unique<TrackConstraintBRVisitor>(
1102           loc::MemRegionVal(RegionRVal), false));
1103     }
1104   }
1105 
1106   return true;
1107 }
1108 
getNilReceiver(const Stmt * S,const ExplodedNode * N)1109 const Expr *NilReceiverBRVisitor::getNilReceiver(const Stmt *S,
1110                                                  const ExplodedNode *N) {
1111   const ObjCMessageExpr *ME = dyn_cast<ObjCMessageExpr>(S);
1112   if (!ME)
1113     return nullptr;
1114   if (const Expr *Receiver = ME->getInstanceReceiver()) {
1115     ProgramStateRef state = N->getState();
1116     SVal V = state->getSVal(Receiver, N->getLocationContext());
1117     if (state->isNull(V).isConstrainedTrue())
1118       return Receiver;
1119   }
1120   return nullptr;
1121 }
1122 
VisitNode(const ExplodedNode * N,const ExplodedNode * PrevN,BugReporterContext & BRC,BugReport & BR)1123 PathDiagnosticPiece *NilReceiverBRVisitor::VisitNode(const ExplodedNode *N,
1124                                                      const ExplodedNode *PrevN,
1125                                                      BugReporterContext &BRC,
1126                                                      BugReport &BR) {
1127   Optional<PreStmt> P = N->getLocationAs<PreStmt>();
1128   if (!P)
1129     return nullptr;
1130 
1131   const Stmt *S = P->getStmt();
1132   const Expr *Receiver = getNilReceiver(S, N);
1133   if (!Receiver)
1134     return nullptr;
1135 
1136   llvm::SmallString<256> Buf;
1137   llvm::raw_svector_ostream OS(Buf);
1138 
1139   if (const ObjCMessageExpr *ME = dyn_cast<ObjCMessageExpr>(S)) {
1140     OS << "'";
1141     ME->getSelector().print(OS);
1142     OS << "' not called";
1143   }
1144   else {
1145     OS << "No method is called";
1146   }
1147   OS << " because the receiver is nil";
1148 
1149   // The receiver was nil, and hence the method was skipped.
1150   // Register a BugReporterVisitor to issue a message telling us how
1151   // the receiver was null.
1152   bugreporter::trackNullOrUndefValue(N, Receiver, BR, /*IsArg*/ false,
1153                                      /*EnableNullFPSuppression*/ false);
1154   // Issue a message saying that the method was skipped.
1155   PathDiagnosticLocation L(Receiver, BRC.getSourceManager(),
1156                                      N->getLocationContext());
1157   return new PathDiagnosticEventPiece(L, OS.str());
1158 }
1159 
1160 // Registers every VarDecl inside a Stmt with a last store visitor.
registerStatementVarDecls(BugReport & BR,const Stmt * S,bool EnableNullFPSuppression)1161 void FindLastStoreBRVisitor::registerStatementVarDecls(BugReport &BR,
1162                                                 const Stmt *S,
1163                                                 bool EnableNullFPSuppression) {
1164   const ExplodedNode *N = BR.getErrorNode();
1165   std::deque<const Stmt *> WorkList;
1166   WorkList.push_back(S);
1167 
1168   while (!WorkList.empty()) {
1169     const Stmt *Head = WorkList.front();
1170     WorkList.pop_front();
1171 
1172     ProgramStateRef state = N->getState();
1173     ProgramStateManager &StateMgr = state->getStateManager();
1174 
1175     if (const DeclRefExpr *DR = dyn_cast<DeclRefExpr>(Head)) {
1176       if (const VarDecl *VD = dyn_cast<VarDecl>(DR->getDecl())) {
1177         const VarRegion *R =
1178         StateMgr.getRegionManager().getVarRegion(VD, N->getLocationContext());
1179 
1180         // What did we load?
1181         SVal V = state->getSVal(S, N->getLocationContext());
1182 
1183         if (V.getAs<loc::ConcreteInt>() || V.getAs<nonloc::ConcreteInt>()) {
1184           // Register a new visitor with the BugReport.
1185           BR.addVisitor(llvm::make_unique<FindLastStoreBRVisitor>(
1186               V.castAs<KnownSVal>(), R, EnableNullFPSuppression));
1187         }
1188       }
1189     }
1190 
1191     for (const Stmt *SubStmt : Head->children())
1192       WorkList.push_back(SubStmt);
1193   }
1194 }
1195 
1196 //===----------------------------------------------------------------------===//
1197 // Visitor that tries to report interesting diagnostics from conditions.
1198 //===----------------------------------------------------------------------===//
1199 
1200 /// Return the tag associated with this visitor.  This tag will be used
1201 /// to make all PathDiagnosticPieces created by this visitor.
getTag()1202 const char *ConditionBRVisitor::getTag() {
1203   return "ConditionBRVisitor";
1204 }
1205 
VisitNode(const ExplodedNode * N,const ExplodedNode * Prev,BugReporterContext & BRC,BugReport & BR)1206 PathDiagnosticPiece *ConditionBRVisitor::VisitNode(const ExplodedNode *N,
1207                                                    const ExplodedNode *Prev,
1208                                                    BugReporterContext &BRC,
1209                                                    BugReport &BR) {
1210   PathDiagnosticPiece *piece = VisitNodeImpl(N, Prev, BRC, BR);
1211   if (piece) {
1212     piece->setTag(getTag());
1213     if (PathDiagnosticEventPiece *ev=dyn_cast<PathDiagnosticEventPiece>(piece))
1214       ev->setPrunable(true, /* override */ false);
1215   }
1216   return piece;
1217 }
1218 
VisitNodeImpl(const ExplodedNode * N,const ExplodedNode * Prev,BugReporterContext & BRC,BugReport & BR)1219 PathDiagnosticPiece *ConditionBRVisitor::VisitNodeImpl(const ExplodedNode *N,
1220                                                        const ExplodedNode *Prev,
1221                                                        BugReporterContext &BRC,
1222                                                        BugReport &BR) {
1223 
1224   ProgramPoint progPoint = N->getLocation();
1225   ProgramStateRef CurrentState = N->getState();
1226   ProgramStateRef PrevState = Prev->getState();
1227 
1228   // Compare the GDMs of the state, because that is where constraints
1229   // are managed.  Note that ensure that we only look at nodes that
1230   // were generated by the analyzer engine proper, not checkers.
1231   if (CurrentState->getGDM().getRoot() ==
1232       PrevState->getGDM().getRoot())
1233     return nullptr;
1234 
1235   // If an assumption was made on a branch, it should be caught
1236   // here by looking at the state transition.
1237   if (Optional<BlockEdge> BE = progPoint.getAs<BlockEdge>()) {
1238     const CFGBlock *srcBlk = BE->getSrc();
1239     if (const Stmt *term = srcBlk->getTerminator())
1240       return VisitTerminator(term, N, srcBlk, BE->getDst(), BR, BRC);
1241     return nullptr;
1242   }
1243 
1244   if (Optional<PostStmt> PS = progPoint.getAs<PostStmt>()) {
1245     // FIXME: Assuming that BugReporter is a GRBugReporter is a layering
1246     // violation.
1247     const std::pair<const ProgramPointTag *, const ProgramPointTag *> &tags =
1248       cast<GRBugReporter>(BRC.getBugReporter()).
1249         getEngine().geteagerlyAssumeBinOpBifurcationTags();
1250 
1251     const ProgramPointTag *tag = PS->getTag();
1252     if (tag == tags.first)
1253       return VisitTrueTest(cast<Expr>(PS->getStmt()), true,
1254                            BRC, BR, N);
1255     if (tag == tags.second)
1256       return VisitTrueTest(cast<Expr>(PS->getStmt()), false,
1257                            BRC, BR, N);
1258 
1259     return nullptr;
1260   }
1261 
1262   return nullptr;
1263 }
1264 
1265 PathDiagnosticPiece *
VisitTerminator(const Stmt * Term,const ExplodedNode * N,const CFGBlock * srcBlk,const CFGBlock * dstBlk,BugReport & R,BugReporterContext & BRC)1266 ConditionBRVisitor::VisitTerminator(const Stmt *Term,
1267                                     const ExplodedNode *N,
1268                                     const CFGBlock *srcBlk,
1269                                     const CFGBlock *dstBlk,
1270                                     BugReport &R,
1271                                     BugReporterContext &BRC) {
1272   const Expr *Cond = nullptr;
1273 
1274   switch (Term->getStmtClass()) {
1275   default:
1276     return nullptr;
1277   case Stmt::IfStmtClass:
1278     Cond = cast<IfStmt>(Term)->getCond();
1279     break;
1280   case Stmt::ConditionalOperatorClass:
1281     Cond = cast<ConditionalOperator>(Term)->getCond();
1282     break;
1283   }
1284 
1285   assert(Cond);
1286   assert(srcBlk->succ_size() == 2);
1287   const bool tookTrue = *(srcBlk->succ_begin()) == dstBlk;
1288   return VisitTrueTest(Cond, tookTrue, BRC, R, N);
1289 }
1290 
1291 PathDiagnosticPiece *
VisitTrueTest(const Expr * Cond,bool tookTrue,BugReporterContext & BRC,BugReport & R,const ExplodedNode * N)1292 ConditionBRVisitor::VisitTrueTest(const Expr *Cond,
1293                                   bool tookTrue,
1294                                   BugReporterContext &BRC,
1295                                   BugReport &R,
1296                                   const ExplodedNode *N) {
1297 
1298   const Expr *Ex = Cond;
1299 
1300   while (true) {
1301     Ex = Ex->IgnoreParenCasts();
1302     switch (Ex->getStmtClass()) {
1303       default:
1304         return nullptr;
1305       case Stmt::BinaryOperatorClass:
1306         return VisitTrueTest(Cond, cast<BinaryOperator>(Ex), tookTrue, BRC,
1307                              R, N);
1308       case Stmt::DeclRefExprClass:
1309         return VisitTrueTest(Cond, cast<DeclRefExpr>(Ex), tookTrue, BRC,
1310                              R, N);
1311       case Stmt::UnaryOperatorClass: {
1312         const UnaryOperator *UO = cast<UnaryOperator>(Ex);
1313         if (UO->getOpcode() == UO_LNot) {
1314           tookTrue = !tookTrue;
1315           Ex = UO->getSubExpr();
1316           continue;
1317         }
1318         return nullptr;
1319       }
1320     }
1321   }
1322 }
1323 
patternMatch(const Expr * Ex,raw_ostream & Out,BugReporterContext & BRC,BugReport & report,const ExplodedNode * N,Optional<bool> & prunable)1324 bool ConditionBRVisitor::patternMatch(const Expr *Ex, raw_ostream &Out,
1325                                       BugReporterContext &BRC,
1326                                       BugReport &report,
1327                                       const ExplodedNode *N,
1328                                       Optional<bool> &prunable) {
1329   const Expr *OriginalExpr = Ex;
1330   Ex = Ex->IgnoreParenCasts();
1331 
1332   if (const DeclRefExpr *DR = dyn_cast<DeclRefExpr>(Ex)) {
1333     const bool quotes = isa<VarDecl>(DR->getDecl());
1334     if (quotes) {
1335       Out << '\'';
1336       const LocationContext *LCtx = N->getLocationContext();
1337       const ProgramState *state = N->getState().get();
1338       if (const MemRegion *R = state->getLValue(cast<VarDecl>(DR->getDecl()),
1339                                                 LCtx).getAsRegion()) {
1340         if (report.isInteresting(R))
1341           prunable = false;
1342         else {
1343           const ProgramState *state = N->getState().get();
1344           SVal V = state->getSVal(R);
1345           if (report.isInteresting(V))
1346             prunable = false;
1347         }
1348       }
1349     }
1350     Out << DR->getDecl()->getDeclName().getAsString();
1351     if (quotes)
1352       Out << '\'';
1353     return quotes;
1354   }
1355 
1356   if (const IntegerLiteral *IL = dyn_cast<IntegerLiteral>(Ex)) {
1357     QualType OriginalTy = OriginalExpr->getType();
1358     if (OriginalTy->isPointerType()) {
1359       if (IL->getValue() == 0) {
1360         Out << "null";
1361         return false;
1362       }
1363     }
1364     else if (OriginalTy->isObjCObjectPointerType()) {
1365       if (IL->getValue() == 0) {
1366         Out << "nil";
1367         return false;
1368       }
1369     }
1370 
1371     Out << IL->getValue();
1372     return false;
1373   }
1374 
1375   return false;
1376 }
1377 
1378 PathDiagnosticPiece *
VisitTrueTest(const Expr * Cond,const BinaryOperator * BExpr,const bool tookTrue,BugReporterContext & BRC,BugReport & R,const ExplodedNode * N)1379 ConditionBRVisitor::VisitTrueTest(const Expr *Cond,
1380                                   const BinaryOperator *BExpr,
1381                                   const bool tookTrue,
1382                                   BugReporterContext &BRC,
1383                                   BugReport &R,
1384                                   const ExplodedNode *N) {
1385 
1386   bool shouldInvert = false;
1387   Optional<bool> shouldPrune;
1388 
1389   SmallString<128> LhsString, RhsString;
1390   {
1391     llvm::raw_svector_ostream OutLHS(LhsString), OutRHS(RhsString);
1392     const bool isVarLHS = patternMatch(BExpr->getLHS(), OutLHS, BRC, R, N,
1393                                        shouldPrune);
1394     const bool isVarRHS = patternMatch(BExpr->getRHS(), OutRHS, BRC, R, N,
1395                                        shouldPrune);
1396 
1397     shouldInvert = !isVarLHS && isVarRHS;
1398   }
1399 
1400   BinaryOperator::Opcode Op = BExpr->getOpcode();
1401 
1402   if (BinaryOperator::isAssignmentOp(Op)) {
1403     // For assignment operators, all that we care about is that the LHS
1404     // evaluates to "true" or "false".
1405     return VisitConditionVariable(LhsString, BExpr->getLHS(), tookTrue,
1406                                   BRC, R, N);
1407   }
1408 
1409   // For non-assignment operations, we require that we can understand
1410   // both the LHS and RHS.
1411   if (LhsString.empty() || RhsString.empty() ||
1412       !BinaryOperator::isComparisonOp(Op))
1413     return nullptr;
1414 
1415   // Should we invert the strings if the LHS is not a variable name?
1416   SmallString<256> buf;
1417   llvm::raw_svector_ostream Out(buf);
1418   Out << "Assuming " << (shouldInvert ? RhsString : LhsString) << " is ";
1419 
1420   // Do we need to invert the opcode?
1421   if (shouldInvert)
1422     switch (Op) {
1423       default: break;
1424       case BO_LT: Op = BO_GT; break;
1425       case BO_GT: Op = BO_LT; break;
1426       case BO_LE: Op = BO_GE; break;
1427       case BO_GE: Op = BO_LE; break;
1428     }
1429 
1430   if (!tookTrue)
1431     switch (Op) {
1432       case BO_EQ: Op = BO_NE; break;
1433       case BO_NE: Op = BO_EQ; break;
1434       case BO_LT: Op = BO_GE; break;
1435       case BO_GT: Op = BO_LE; break;
1436       case BO_LE: Op = BO_GT; break;
1437       case BO_GE: Op = BO_LT; break;
1438       default:
1439         return nullptr;
1440     }
1441 
1442   switch (Op) {
1443     case BO_EQ:
1444       Out << "equal to ";
1445       break;
1446     case BO_NE:
1447       Out << "not equal to ";
1448       break;
1449     default:
1450       Out << BinaryOperator::getOpcodeStr(Op) << ' ';
1451       break;
1452   }
1453 
1454   Out << (shouldInvert ? LhsString : RhsString);
1455   const LocationContext *LCtx = N->getLocationContext();
1456   PathDiagnosticLocation Loc(Cond, BRC.getSourceManager(), LCtx);
1457   PathDiagnosticEventPiece *event =
1458     new PathDiagnosticEventPiece(Loc, Out.str());
1459   if (shouldPrune.hasValue())
1460     event->setPrunable(shouldPrune.getValue());
1461   return event;
1462 }
1463 
1464 PathDiagnosticPiece *
VisitConditionVariable(StringRef LhsString,const Expr * CondVarExpr,const bool tookTrue,BugReporterContext & BRC,BugReport & report,const ExplodedNode * N)1465 ConditionBRVisitor::VisitConditionVariable(StringRef LhsString,
1466                                            const Expr *CondVarExpr,
1467                                            const bool tookTrue,
1468                                            BugReporterContext &BRC,
1469                                            BugReport &report,
1470                                            const ExplodedNode *N) {
1471   // FIXME: If there's already a constraint tracker for this variable,
1472   // we shouldn't emit anything here (c.f. the double note in
1473   // test/Analysis/inlining/path-notes.c)
1474   SmallString<256> buf;
1475   llvm::raw_svector_ostream Out(buf);
1476   Out << "Assuming " << LhsString << " is ";
1477 
1478   QualType Ty = CondVarExpr->getType();
1479 
1480   if (Ty->isPointerType())
1481     Out << (tookTrue ? "not null" : "null");
1482   else if (Ty->isObjCObjectPointerType())
1483     Out << (tookTrue ? "not nil" : "nil");
1484   else if (Ty->isBooleanType())
1485     Out << (tookTrue ? "true" : "false");
1486   else if (Ty->isIntegralOrEnumerationType())
1487     Out << (tookTrue ? "non-zero" : "zero");
1488   else
1489     return nullptr;
1490 
1491   const LocationContext *LCtx = N->getLocationContext();
1492   PathDiagnosticLocation Loc(CondVarExpr, BRC.getSourceManager(), LCtx);
1493   PathDiagnosticEventPiece *event =
1494     new PathDiagnosticEventPiece(Loc, Out.str());
1495 
1496   if (const DeclRefExpr *DR = dyn_cast<DeclRefExpr>(CondVarExpr)) {
1497     if (const VarDecl *VD = dyn_cast<VarDecl>(DR->getDecl())) {
1498       const ProgramState *state = N->getState().get();
1499       if (const MemRegion *R = state->getLValue(VD, LCtx).getAsRegion()) {
1500         if (report.isInteresting(R))
1501           event->setPrunable(false);
1502       }
1503     }
1504   }
1505 
1506   return event;
1507 }
1508 
1509 PathDiagnosticPiece *
VisitTrueTest(const Expr * Cond,const DeclRefExpr * DR,const bool tookTrue,BugReporterContext & BRC,BugReport & report,const ExplodedNode * N)1510 ConditionBRVisitor::VisitTrueTest(const Expr *Cond,
1511                                   const DeclRefExpr *DR,
1512                                   const bool tookTrue,
1513                                   BugReporterContext &BRC,
1514                                   BugReport &report,
1515                                   const ExplodedNode *N) {
1516 
1517   const VarDecl *VD = dyn_cast<VarDecl>(DR->getDecl());
1518   if (!VD)
1519     return nullptr;
1520 
1521   SmallString<256> Buf;
1522   llvm::raw_svector_ostream Out(Buf);
1523 
1524   Out << "Assuming '" << VD->getDeclName() << "' is ";
1525 
1526   QualType VDTy = VD->getType();
1527 
1528   if (VDTy->isPointerType())
1529     Out << (tookTrue ? "non-null" : "null");
1530   else if (VDTy->isObjCObjectPointerType())
1531     Out << (tookTrue ? "non-nil" : "nil");
1532   else if (VDTy->isScalarType())
1533     Out << (tookTrue ? "not equal to 0" : "0");
1534   else
1535     return nullptr;
1536 
1537   const LocationContext *LCtx = N->getLocationContext();
1538   PathDiagnosticLocation Loc(Cond, BRC.getSourceManager(), LCtx);
1539   PathDiagnosticEventPiece *event =
1540     new PathDiagnosticEventPiece(Loc, Out.str());
1541 
1542   const ProgramState *state = N->getState().get();
1543   if (const MemRegion *R = state->getLValue(VD, LCtx).getAsRegion()) {
1544     if (report.isInteresting(R))
1545       event->setPrunable(false);
1546     else {
1547       SVal V = state->getSVal(R);
1548       if (report.isInteresting(V))
1549         event->setPrunable(false);
1550     }
1551   }
1552   return event;
1553 }
1554 
1555 std::unique_ptr<PathDiagnosticPiece>
getEndPath(BugReporterContext & BRC,const ExplodedNode * N,BugReport & BR)1556 LikelyFalsePositiveSuppressionBRVisitor::getEndPath(BugReporterContext &BRC,
1557                                                     const ExplodedNode *N,
1558                                                     BugReport &BR) {
1559   // Here we suppress false positives coming from system headers. This list is
1560   // based on known issues.
1561   ExprEngine &Eng = BRC.getBugReporter().getEngine();
1562   AnalyzerOptions &Options = Eng.getAnalysisManager().options;
1563   const Decl *D = N->getLocationContext()->getDecl();
1564 
1565   if (AnalysisDeclContext::isInStdNamespace(D)) {
1566     // Skip reports within the 'std' namespace. Although these can sometimes be
1567     // the user's fault, we currently don't report them very well, and
1568     // Note that this will not help for any other data structure libraries, like
1569     // TR1, Boost, or llvm/ADT.
1570     if (Options.shouldSuppressFromCXXStandardLibrary()) {
1571       BR.markInvalid(getTag(), nullptr);
1572       return nullptr;
1573 
1574     } else {
1575       // If the complete 'std' suppression is not enabled, suppress reports
1576       // from the 'std' namespace that are known to produce false positives.
1577 
1578       // The analyzer issues a false use-after-free when std::list::pop_front
1579       // or std::list::pop_back are called multiple times because we cannot
1580       // reason about the internal invariants of the datastructure.
1581       if (const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(D)) {
1582         const CXXRecordDecl *CD = MD->getParent();
1583         if (CD->getName() == "list") {
1584           BR.markInvalid(getTag(), nullptr);
1585           return nullptr;
1586         }
1587       }
1588 
1589       // The analyzer issues a false positive when the constructor of
1590       // std::__independent_bits_engine from algorithms is used.
1591       if (const CXXConstructorDecl *MD = dyn_cast<CXXConstructorDecl>(D)) {
1592         const CXXRecordDecl *CD = MD->getParent();
1593         if (CD->getName() == "__independent_bits_engine") {
1594           BR.markInvalid(getTag(), nullptr);
1595           return nullptr;
1596         }
1597       }
1598 
1599       for (const LocationContext *LCtx = N->getLocationContext(); LCtx;
1600            LCtx = LCtx->getParent()) {
1601         const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(LCtx->getDecl());
1602         if (!MD)
1603           continue;
1604 
1605         const CXXRecordDecl *CD = MD->getParent();
1606         // The analyzer issues a false positive on
1607         //   std::basic_string<uint8_t> v; v.push_back(1);
1608         // and
1609         //   std::u16string s; s += u'a';
1610         // because we cannot reason about the internal invariants of the
1611         // datastructure.
1612         if (CD->getName() == "basic_string") {
1613           BR.markInvalid(getTag(), nullptr);
1614           return nullptr;
1615         }
1616 
1617         // The analyzer issues a false positive on
1618         //    std::shared_ptr<int> p(new int(1)); p = nullptr;
1619         // because it does not reason properly about temporary destructors.
1620         if (CD->getName() == "shared_ptr") {
1621           BR.markInvalid(getTag(), nullptr);
1622           return nullptr;
1623         }
1624       }
1625     }
1626   }
1627 
1628   // Skip reports within the sys/queue.h macros as we do not have the ability to
1629   // reason about data structure shapes.
1630   SourceManager &SM = BRC.getSourceManager();
1631   FullSourceLoc Loc = BR.getLocation(SM).asLocation();
1632   while (Loc.isMacroID()) {
1633     Loc = Loc.getSpellingLoc();
1634     if (SM.getFilename(Loc).endswith("sys/queue.h")) {
1635       BR.markInvalid(getTag(), nullptr);
1636       return nullptr;
1637     }
1638   }
1639 
1640   return nullptr;
1641 }
1642 
1643 PathDiagnosticPiece *
VisitNode(const ExplodedNode * N,const ExplodedNode * PrevN,BugReporterContext & BRC,BugReport & BR)1644 UndefOrNullArgVisitor::VisitNode(const ExplodedNode *N,
1645                                   const ExplodedNode *PrevN,
1646                                   BugReporterContext &BRC,
1647                                   BugReport &BR) {
1648 
1649   ProgramStateRef State = N->getState();
1650   ProgramPoint ProgLoc = N->getLocation();
1651 
1652   // We are only interested in visiting CallEnter nodes.
1653   Optional<CallEnter> CEnter = ProgLoc.getAs<CallEnter>();
1654   if (!CEnter)
1655     return nullptr;
1656 
1657   // Check if one of the arguments is the region the visitor is tracking.
1658   CallEventManager &CEMgr = BRC.getStateManager().getCallEventManager();
1659   CallEventRef<> Call = CEMgr.getCaller(CEnter->getCalleeContext(), State);
1660   unsigned Idx = 0;
1661   ArrayRef<ParmVarDecl*> parms = Call->parameters();
1662 
1663   for (ArrayRef<ParmVarDecl*>::iterator I = parms.begin(), E = parms.end();
1664                               I != E; ++I, ++Idx) {
1665     const MemRegion *ArgReg = Call->getArgSVal(Idx).getAsRegion();
1666 
1667     // Are we tracking the argument or its subregion?
1668     if ( !ArgReg || (ArgReg != R && !R->isSubRegionOf(ArgReg->StripCasts())))
1669       continue;
1670 
1671     // Check the function parameter type.
1672     const ParmVarDecl *ParamDecl = *I;
1673     assert(ParamDecl && "Formal parameter has no decl?");
1674     QualType T = ParamDecl->getType();
1675 
1676     if (!(T->isAnyPointerType() || T->isReferenceType())) {
1677       // Function can only change the value passed in by address.
1678       continue;
1679     }
1680 
1681     // If it is a const pointer value, the function does not intend to
1682     // change the value.
1683     if (T->getPointeeType().isConstQualified())
1684       continue;
1685 
1686     // Mark the call site (LocationContext) as interesting if the value of the
1687     // argument is undefined or '0'/'NULL'.
1688     SVal BoundVal = State->getSVal(R);
1689     if (BoundVal.isUndef() || BoundVal.isZeroConstant()) {
1690       BR.markInteresting(CEnter->getCalleeContext());
1691       return nullptr;
1692     }
1693   }
1694   return nullptr;
1695 }
1696