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Diffstat (limited to 'clang/lib/StaticAnalyzer/Checkers/NullabilityChecker.cpp')
| -rw-r--r-- | clang/lib/StaticAnalyzer/Checkers/NullabilityChecker.cpp | 1225 |
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diff --git a/clang/lib/StaticAnalyzer/Checkers/NullabilityChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/NullabilityChecker.cpp new file mode 100644 index 000000000000..4322ac207112 --- /dev/null +++ b/clang/lib/StaticAnalyzer/Checkers/NullabilityChecker.cpp @@ -0,0 +1,1225 @@ +//===-- NullabilityChecker.cpp - Nullability checker ----------------------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// +// +// This checker tries to find nullability violations. There are several kinds of +// possible violations: +// * Null pointer is passed to a pointer which has a _Nonnull type. +// * Null pointer is returned from a function which has a _Nonnull return type. +// * Nullable pointer is passed to a pointer which has a _Nonnull type. +// * Nullable pointer is returned from a function which has a _Nonnull return +// type. +// * Nullable pointer is dereferenced. +// +// This checker propagates the nullability information of the pointers and looks +// for the patterns that are described above. Explicit casts are trusted and are +// considered a way to suppress false positives for this checker. The other way +// to suppress warnings would be to add asserts or guarding if statements to the +// code. In addition to the nullability propagation this checker also uses some +// heuristics to suppress potential false positives. +// +//===----------------------------------------------------------------------===// + +#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h" + +#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h" +#include "clang/StaticAnalyzer/Core/Checker.h" +#include "clang/StaticAnalyzer/Core/CheckerManager.h" +#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerHelpers.h" +#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h" +#include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h" + +#include "llvm/ADT/StringExtras.h" +#include "llvm/Support/Path.h" + +using namespace clang; +using namespace ento; + +namespace { + +/// Returns the most nullable nullability. This is used for message expressions +/// like [receiver method], where the nullability of this expression is either +/// the nullability of the receiver or the nullability of the return type of the +/// method, depending on which is more nullable. Contradicted is considered to +/// be the most nullable, to avoid false positive results. +Nullability getMostNullable(Nullability Lhs, Nullability Rhs) { + return static_cast<Nullability>( + std::min(static_cast<char>(Lhs), static_cast<char>(Rhs))); +} + +const char *getNullabilityString(Nullability Nullab) { + switch (Nullab) { + case Nullability::Contradicted: + return "contradicted"; + case Nullability::Nullable: + return "nullable"; + case Nullability::Unspecified: + return "unspecified"; + case Nullability::Nonnull: + return "nonnull"; + } + llvm_unreachable("Unexpected enumeration."); + return ""; +} + +// These enums are used as an index to ErrorMessages array. +enum class ErrorKind : int { + NilAssignedToNonnull, + NilPassedToNonnull, + NilReturnedToNonnull, + NullableAssignedToNonnull, + NullableReturnedToNonnull, + NullableDereferenced, + NullablePassedToNonnull +}; + +class NullabilityChecker + : public Checker<check::Bind, check::PreCall, check::PreStmt<ReturnStmt>, + check::PostCall, check::PostStmt<ExplicitCastExpr>, + check::PostObjCMessage, check::DeadSymbols, + check::Event<ImplicitNullDerefEvent>> { + mutable std::unique_ptr<BugType> BT; + +public: + // If true, the checker will not diagnose nullabilility issues for calls + // to system headers. This option is motivated by the observation that large + // projects may have many nullability warnings. These projects may + // find warnings about nullability annotations that they have explicitly + // added themselves higher priority to fix than warnings on calls to system + // libraries. + DefaultBool NoDiagnoseCallsToSystemHeaders; + + void checkBind(SVal L, SVal V, const Stmt *S, CheckerContext &C) const; + void checkPostStmt(const ExplicitCastExpr *CE, CheckerContext &C) const; + void checkPreStmt(const ReturnStmt *S, CheckerContext &C) const; + void checkPostObjCMessage(const ObjCMethodCall &M, CheckerContext &C) const; + void checkPostCall(const CallEvent &Call, CheckerContext &C) const; + void checkPreCall(const CallEvent &Call, CheckerContext &C) const; + void checkDeadSymbols(SymbolReaper &SR, CheckerContext &C) const; + void checkEvent(ImplicitNullDerefEvent Event) const; + + void printState(raw_ostream &Out, ProgramStateRef State, const char *NL, + const char *Sep) const override; + + struct NullabilityChecksFilter { + DefaultBool CheckNullPassedToNonnull; + DefaultBool CheckNullReturnedFromNonnull; + DefaultBool CheckNullableDereferenced; + DefaultBool CheckNullablePassedToNonnull; + DefaultBool CheckNullableReturnedFromNonnull; + + CheckerNameRef CheckNameNullPassedToNonnull; + CheckerNameRef CheckNameNullReturnedFromNonnull; + CheckerNameRef CheckNameNullableDereferenced; + CheckerNameRef CheckNameNullablePassedToNonnull; + CheckerNameRef CheckNameNullableReturnedFromNonnull; + }; + + NullabilityChecksFilter Filter; + // When set to false no nullability information will be tracked in + // NullabilityMap. It is possible to catch errors like passing a null pointer + // to a callee that expects nonnull argument without the information that is + // stroed in the NullabilityMap. This is an optimization. + DefaultBool NeedTracking; + +private: + class NullabilityBugVisitor : public BugReporterVisitor { + public: + NullabilityBugVisitor(const MemRegion *M) : Region(M) {} + + void Profile(llvm::FoldingSetNodeID &ID) const override { + static int X = 0; + ID.AddPointer(&X); + ID.AddPointer(Region); + } + + PathDiagnosticPieceRef VisitNode(const ExplodedNode *N, + BugReporterContext &BRC, + PathSensitiveBugReport &BR) override; + + private: + // The tracked region. + const MemRegion *Region; + }; + + /// When any of the nonnull arguments of the analyzed function is null, do not + /// report anything and turn off the check. + /// + /// When \p SuppressPath is set to true, no more bugs will be reported on this + /// path by this checker. + void reportBugIfInvariantHolds(StringRef Msg, ErrorKind Error, + ExplodedNode *N, const MemRegion *Region, + CheckerContext &C, + const Stmt *ValueExpr = nullptr, + bool SuppressPath = false) const; + + void reportBug(StringRef Msg, ErrorKind Error, ExplodedNode *N, + const MemRegion *Region, BugReporter &BR, + const Stmt *ValueExpr = nullptr) const { + if (!BT) + BT.reset(new BugType(this, "Nullability", categories::MemoryError)); + + auto R = std::make_unique<PathSensitiveBugReport>(*BT, Msg, N); + if (Region) { + R->markInteresting(Region); + R->addVisitor(std::make_unique<NullabilityBugVisitor>(Region)); + } + if (ValueExpr) { + R->addRange(ValueExpr->getSourceRange()); + if (Error == ErrorKind::NilAssignedToNonnull || + Error == ErrorKind::NilPassedToNonnull || + Error == ErrorKind::NilReturnedToNonnull) + if (const auto *Ex = dyn_cast<Expr>(ValueExpr)) + bugreporter::trackExpressionValue(N, Ex, *R); + } + BR.emitReport(std::move(R)); + } + + /// If an SVal wraps a region that should be tracked, it will return a pointer + /// to the wrapped region. Otherwise it will return a nullptr. + const SymbolicRegion *getTrackRegion(SVal Val, + bool CheckSuperRegion = false) const; + + /// Returns true if the call is diagnosable in the current analyzer + /// configuration. + bool isDiagnosableCall(const CallEvent &Call) const { + if (NoDiagnoseCallsToSystemHeaders && Call.isInSystemHeader()) + return false; + + return true; + } +}; + +class NullabilityState { +public: + NullabilityState(Nullability Nullab, const Stmt *Source = nullptr) + : Nullab(Nullab), Source(Source) {} + + const Stmt *getNullabilitySource() const { return Source; } + + Nullability getValue() const { return Nullab; } + + void Profile(llvm::FoldingSetNodeID &ID) const { + ID.AddInteger(static_cast<char>(Nullab)); + ID.AddPointer(Source); + } + + void print(raw_ostream &Out) const { + Out << getNullabilityString(Nullab) << "\n"; + } + +private: + Nullability Nullab; + // Source is the expression which determined the nullability. For example in a + // message like [nullable nonnull_returning] has nullable nullability, because + // the receiver is nullable. Here the receiver will be the source of the + // nullability. This is useful information when the diagnostics are generated. + const Stmt *Source; +}; + +bool operator==(NullabilityState Lhs, NullabilityState Rhs) { + return Lhs.getValue() == Rhs.getValue() && + Lhs.getNullabilitySource() == Rhs.getNullabilitySource(); +} + +} // end anonymous namespace + +REGISTER_MAP_WITH_PROGRAMSTATE(NullabilityMap, const MemRegion *, + NullabilityState) + +// We say "the nullability type invariant is violated" when a location with a +// non-null type contains NULL or a function with a non-null return type returns +// NULL. Violations of the nullability type invariant can be detected either +// directly (for example, when NULL is passed as an argument to a nonnull +// parameter) or indirectly (for example, when, inside a function, the +// programmer defensively checks whether a nonnull parameter contains NULL and +// finds that it does). +// +// As a matter of policy, the nullability checker typically warns on direct +// violations of the nullability invariant (although it uses various +// heuristics to suppress warnings in some cases) but will not warn if the +// invariant has already been violated along the path (either directly or +// indirectly). As a practical matter, this prevents the analyzer from +// (1) warning on defensive code paths where a nullability precondition is +// determined to have been violated, (2) warning additional times after an +// initial direct violation has been discovered, and (3) warning after a direct +// violation that has been implicitly or explicitly suppressed (for +// example, with a cast of NULL to _Nonnull). In essence, once an invariant +// violation is detected on a path, this checker will be essentially turned off +// for the rest of the analysis +// +// The analyzer takes this approach (rather than generating a sink node) to +// ensure coverage of defensive paths, which may be important for backwards +// compatibility in codebases that were developed without nullability in mind. +REGISTER_TRAIT_WITH_PROGRAMSTATE(InvariantViolated, bool) + +enum class NullConstraint { IsNull, IsNotNull, Unknown }; + +static NullConstraint getNullConstraint(DefinedOrUnknownSVal Val, + ProgramStateRef State) { + ConditionTruthVal Nullness = State->isNull(Val); + if (Nullness.isConstrainedFalse()) + return NullConstraint::IsNotNull; + if (Nullness.isConstrainedTrue()) + return NullConstraint::IsNull; + return NullConstraint::Unknown; +} + +const SymbolicRegion * +NullabilityChecker::getTrackRegion(SVal Val, bool CheckSuperRegion) const { + if (!NeedTracking) + return nullptr; + + auto RegionSVal = Val.getAs<loc::MemRegionVal>(); + if (!RegionSVal) + return nullptr; + + const MemRegion *Region = RegionSVal->getRegion(); + + if (CheckSuperRegion) { + if (auto FieldReg = Region->getAs<FieldRegion>()) + return dyn_cast<SymbolicRegion>(FieldReg->getSuperRegion()); + if (auto ElementReg = Region->getAs<ElementRegion>()) + return dyn_cast<SymbolicRegion>(ElementReg->getSuperRegion()); + } + + return dyn_cast<SymbolicRegion>(Region); +} + +PathDiagnosticPieceRef NullabilityChecker::NullabilityBugVisitor::VisitNode( + const ExplodedNode *N, BugReporterContext &BRC, + PathSensitiveBugReport &BR) { + ProgramStateRef State = N->getState(); + ProgramStateRef StatePrev = N->getFirstPred()->getState(); + + const NullabilityState *TrackedNullab = State->get<NullabilityMap>(Region); + const NullabilityState *TrackedNullabPrev = + StatePrev->get<NullabilityMap>(Region); + if (!TrackedNullab) + return nullptr; + + if (TrackedNullabPrev && + TrackedNullabPrev->getValue() == TrackedNullab->getValue()) + return nullptr; + + // Retrieve the associated statement. + const Stmt *S = TrackedNullab->getNullabilitySource(); + if (!S || S->getBeginLoc().isInvalid()) { + S = N->getStmtForDiagnostics(); + } + + if (!S) + return nullptr; + + std::string InfoText = + (llvm::Twine("Nullability '") + + getNullabilityString(TrackedNullab->getValue()) + "' is inferred") + .str(); + + // Generate the extra diagnostic. + PathDiagnosticLocation Pos(S, BRC.getSourceManager(), + N->getLocationContext()); + return std::make_shared<PathDiagnosticEventPiece>(Pos, InfoText, true); +} + +/// Returns true when the value stored at the given location has been +/// constrained to null after being passed through an object of nonnnull type. +static bool checkValueAtLValForInvariantViolation(ProgramStateRef State, + SVal LV, QualType T) { + if (getNullabilityAnnotation(T) != Nullability::Nonnull) + return false; + + auto RegionVal = LV.getAs<loc::MemRegionVal>(); + if (!RegionVal) + return false; + + // If the value was constrained to null *after* it was passed through that + // location, it could not have been a concrete pointer *when* it was passed. + // In that case we would have handled the situation when the value was + // bound to that location, by emitting (or not emitting) a report. + // Therefore we are only interested in symbolic regions that can be either + // null or non-null depending on the value of their respective symbol. + auto StoredVal = State->getSVal(*RegionVal).getAs<loc::MemRegionVal>(); + if (!StoredVal || !isa<SymbolicRegion>(StoredVal->getRegion())) + return false; + + if (getNullConstraint(*StoredVal, State) == NullConstraint::IsNull) + return true; + + return false; +} + +static bool +checkParamsForPreconditionViolation(ArrayRef<ParmVarDecl *> Params, + ProgramStateRef State, + const LocationContext *LocCtxt) { + for (const auto *ParamDecl : Params) { + if (ParamDecl->isParameterPack()) + break; + + SVal LV = State->getLValue(ParamDecl, LocCtxt); + if (checkValueAtLValForInvariantViolation(State, LV, + ParamDecl->getType())) { + return true; + } + } + return false; +} + +static bool +checkSelfIvarsForInvariantViolation(ProgramStateRef State, + const LocationContext *LocCtxt) { + auto *MD = dyn_cast<ObjCMethodDecl>(LocCtxt->getDecl()); + if (!MD || !MD->isInstanceMethod()) + return false; + + const ImplicitParamDecl *SelfDecl = LocCtxt->getSelfDecl(); + if (!SelfDecl) + return false; + + SVal SelfVal = State->getSVal(State->getRegion(SelfDecl, LocCtxt)); + + const ObjCObjectPointerType *SelfType = + dyn_cast<ObjCObjectPointerType>(SelfDecl->getType()); + if (!SelfType) + return false; + + const ObjCInterfaceDecl *ID = SelfType->getInterfaceDecl(); + if (!ID) + return false; + + for (const auto *IvarDecl : ID->ivars()) { + SVal LV = State->getLValue(IvarDecl, SelfVal); + if (checkValueAtLValForInvariantViolation(State, LV, IvarDecl->getType())) { + return true; + } + } + return false; +} + +static bool checkInvariantViolation(ProgramStateRef State, ExplodedNode *N, + CheckerContext &C) { + if (State->get<InvariantViolated>()) + return true; + + const LocationContext *LocCtxt = C.getLocationContext(); + const Decl *D = LocCtxt->getDecl(); + if (!D) + return false; + + ArrayRef<ParmVarDecl*> Params; + if (const auto *BD = dyn_cast<BlockDecl>(D)) + Params = BD->parameters(); + else if (const auto *FD = dyn_cast<FunctionDecl>(D)) + Params = FD->parameters(); + else if (const auto *MD = dyn_cast<ObjCMethodDecl>(D)) + Params = MD->parameters(); + else + return false; + + if (checkParamsForPreconditionViolation(Params, State, LocCtxt) || + checkSelfIvarsForInvariantViolation(State, LocCtxt)) { + if (!N->isSink()) + C.addTransition(State->set<InvariantViolated>(true), N); + return true; + } + return false; +} + +void NullabilityChecker::reportBugIfInvariantHolds(StringRef Msg, + ErrorKind Error, ExplodedNode *N, const MemRegion *Region, + CheckerContext &C, const Stmt *ValueExpr, bool SuppressPath) const { + ProgramStateRef OriginalState = N->getState(); + + if (checkInvariantViolation(OriginalState, N, C)) + return; + if (SuppressPath) { + OriginalState = OriginalState->set<InvariantViolated>(true); + N = C.addTransition(OriginalState, N); + } + + reportBug(Msg, Error, N, Region, C.getBugReporter(), ValueExpr); +} + +/// Cleaning up the program state. +void NullabilityChecker::checkDeadSymbols(SymbolReaper &SR, + CheckerContext &C) const { + ProgramStateRef State = C.getState(); + NullabilityMapTy Nullabilities = State->get<NullabilityMap>(); + for (NullabilityMapTy::iterator I = Nullabilities.begin(), + E = Nullabilities.end(); + I != E; ++I) { + const auto *Region = I->first->getAs<SymbolicRegion>(); + assert(Region && "Non-symbolic region is tracked."); + if (SR.isDead(Region->getSymbol())) { + State = State->remove<NullabilityMap>(I->first); + } + } + // When one of the nonnull arguments are constrained to be null, nullability + // preconditions are violated. It is not enough to check this only when we + // actually report an error, because at that time interesting symbols might be + // reaped. + if (checkInvariantViolation(State, C.getPredecessor(), C)) + return; + C.addTransition(State); +} + +/// This callback triggers when a pointer is dereferenced and the analyzer does +/// not know anything about the value of that pointer. When that pointer is +/// nullable, this code emits a warning. +void NullabilityChecker::checkEvent(ImplicitNullDerefEvent Event) const { + if (Event.SinkNode->getState()->get<InvariantViolated>()) + return; + + const MemRegion *Region = + getTrackRegion(Event.Location, /*CheckSuperRegion=*/true); + if (!Region) + return; + + ProgramStateRef State = Event.SinkNode->getState(); + const NullabilityState *TrackedNullability = + State->get<NullabilityMap>(Region); + + if (!TrackedNullability) + return; + + if (Filter.CheckNullableDereferenced && + TrackedNullability->getValue() == Nullability::Nullable) { + BugReporter &BR = *Event.BR; + // Do not suppress errors on defensive code paths, because dereferencing + // a nullable pointer is always an error. + if (Event.IsDirectDereference) + reportBug("Nullable pointer is dereferenced", + ErrorKind::NullableDereferenced, Event.SinkNode, Region, BR); + else { + reportBug("Nullable pointer is passed to a callee that requires a " + "non-null", ErrorKind::NullablePassedToNonnull, + Event.SinkNode, Region, BR); + } + } +} + +/// Find the outermost subexpression of E that is not an implicit cast. +/// This looks through the implicit casts to _Nonnull that ARC adds to +/// return expressions of ObjC types when the return type of the function or +/// method is non-null but the express is not. +static const Expr *lookThroughImplicitCasts(const Expr *E) { + assert(E); + + while (auto *ICE = dyn_cast<ImplicitCastExpr>(E)) { + E = ICE->getSubExpr(); + } + + return E; +} + +/// This method check when nullable pointer or null value is returned from a +/// function that has nonnull return type. +void NullabilityChecker::checkPreStmt(const ReturnStmt *S, + CheckerContext &C) const { + auto RetExpr = S->getRetValue(); + if (!RetExpr) + return; + + if (!RetExpr->getType()->isAnyPointerType()) + return; + + ProgramStateRef State = C.getState(); + if (State->get<InvariantViolated>()) + return; + + auto RetSVal = C.getSVal(S).getAs<DefinedOrUnknownSVal>(); + if (!RetSVal) + return; + + bool InSuppressedMethodFamily = false; + + QualType RequiredRetType; + AnalysisDeclContext *DeclCtxt = + C.getLocationContext()->getAnalysisDeclContext(); + const Decl *D = DeclCtxt->getDecl(); + if (auto *MD = dyn_cast<ObjCMethodDecl>(D)) { + // HACK: This is a big hammer to avoid warning when there are defensive + // nil checks in -init and -copy methods. We should add more sophisticated + // logic here to suppress on common defensive idioms but still + // warn when there is a likely problem. + ObjCMethodFamily Family = MD->getMethodFamily(); + if (OMF_init == Family || OMF_copy == Family || OMF_mutableCopy == Family) + InSuppressedMethodFamily = true; + + RequiredRetType = MD->getReturnType(); + } else if (auto *FD = dyn_cast<FunctionDecl>(D)) { + RequiredRetType = FD->getReturnType(); + } else { + return; + } + + NullConstraint Nullness = getNullConstraint(*RetSVal, State); + + Nullability RequiredNullability = getNullabilityAnnotation(RequiredRetType); + + // If the returned value is null but the type of the expression + // generating it is nonnull then we will suppress the diagnostic. + // This enables explicit suppression when returning a nil literal in a + // function with a _Nonnull return type: + // return (NSString * _Nonnull)0; + Nullability RetExprTypeLevelNullability = + getNullabilityAnnotation(lookThroughImplicitCasts(RetExpr)->getType()); + + bool NullReturnedFromNonNull = (RequiredNullability == Nullability::Nonnull && + Nullness == NullConstraint::IsNull); + if (Filter.CheckNullReturnedFromNonnull && + NullReturnedFromNonNull && + RetExprTypeLevelNullability != Nullability::Nonnull && + !InSuppressedMethodFamily && + C.getLocationContext()->inTopFrame()) { + static CheckerProgramPointTag Tag(this, "NullReturnedFromNonnull"); + ExplodedNode *N = C.generateErrorNode(State, &Tag); + if (!N) + return; + + SmallString<256> SBuf; + llvm::raw_svector_ostream OS(SBuf); + OS << (RetExpr->getType()->isObjCObjectPointerType() ? "nil" : "Null"); + OS << " returned from a " << C.getDeclDescription(D) << + " that is expected to return a non-null value"; + reportBugIfInvariantHolds(OS.str(), + ErrorKind::NilReturnedToNonnull, N, nullptr, C, + RetExpr); + return; + } + + // If null was returned from a non-null function, mark the nullability + // invariant as violated even if the diagnostic was suppressed. + if (NullReturnedFromNonNull) { + State = State->set<InvariantViolated>(true); + C.addTransition(State); + return; + } + + const MemRegion *Region = getTrackRegion(*RetSVal); + if (!Region) + return; + + const NullabilityState *TrackedNullability = + State->get<NullabilityMap>(Region); + if (TrackedNullability) { + Nullability TrackedNullabValue = TrackedNullability->getValue(); + if (Filter.CheckNullableReturnedFromNonnull && + Nullness != NullConstraint::IsNotNull && + TrackedNullabValue == Nullability::Nullable && + RequiredNullability == Nullability::Nonnull) { + static CheckerProgramPointTag Tag(this, "NullableReturnedFromNonnull"); + ExplodedNode *N = C.addTransition(State, C.getPredecessor(), &Tag); + + SmallString<256> SBuf; + llvm::raw_svector_ostream OS(SBuf); + OS << "Nullable pointer is returned from a " << C.getDeclDescription(D) << + " that is expected to return a non-null value"; + + reportBugIfInvariantHolds(OS.str(), + ErrorKind::NullableReturnedToNonnull, N, + Region, C); + } + return; + } + if (RequiredNullability == Nullability::Nullable) { + State = State->set<NullabilityMap>(Region, + NullabilityState(RequiredNullability, + S)); + C.addTransition(State); + } +} + +/// This callback warns when a nullable pointer or a null value is passed to a +/// function that expects its argument to be nonnull. +void NullabilityChecker::checkPreCall(const CallEvent &Call, + CheckerContext &C) const { + if (!Call.getDecl()) + return; + + ProgramStateRef State = C.getState(); + if (State->get<InvariantViolated>()) + return; + + ProgramStateRef OrigState = State; + + unsigned Idx = 0; + for (const ParmVarDecl *Param : Call.parameters()) { + if (Param->isParameterPack()) + break; + + if (Idx >= Call.getNumArgs()) + break; + + const Expr *ArgExpr = Call.getArgExpr(Idx); + auto ArgSVal = Call.getArgSVal(Idx++).getAs<DefinedOrUnknownSVal>(); + if (!ArgSVal) + continue; + + if (!Param->getType()->isAnyPointerType() && + !Param->getType()->isReferenceType()) + continue; + + NullConstraint Nullness = getNullConstraint(*ArgSVal, State); + + Nullability RequiredNullability = + getNullabilityAnnotation(Param->getType()); + Nullability ArgExprTypeLevelNullability = + getNullabilityAnnotation(ArgExpr->getType()); + + unsigned ParamIdx = Param->getFunctionScopeIndex() + 1; + + if (Filter.CheckNullPassedToNonnull && Nullness == NullConstraint::IsNull && + ArgExprTypeLevelNullability != Nullability::Nonnull && + RequiredNullability == Nullability::Nonnull && + isDiagnosableCall(Call)) { + ExplodedNode *N = C.generateErrorNode(State); + if (!N) + return; + + SmallString<256> SBuf; + llvm::raw_svector_ostream OS(SBuf); + OS << (Param->getType()->isObjCObjectPointerType() ? "nil" : "Null"); + OS << " passed to a callee that requires a non-null " << ParamIdx + << llvm::getOrdinalSuffix(ParamIdx) << " parameter"; + reportBugIfInvariantHolds(OS.str(), ErrorKind::NilPassedToNonnull, N, + nullptr, C, + ArgExpr, /*SuppressPath=*/false); + return; + } + + const MemRegion *Region = getTrackRegion(*ArgSVal); + if (!Region) + continue; + + const NullabilityState *TrackedNullability = + State->get<NullabilityMap>(Region); + + if (TrackedNullability) { + if (Nullness == NullConstraint::IsNotNull || + TrackedNullability->getValue() != Nullability::Nullable) + continue; + + if (Filter.CheckNullablePassedToNonnull && + RequiredNullability == Nullability::Nonnull && + isDiagnosableCall(Call)) { + ExplodedNode *N = C.addTransition(State); + SmallString<256> SBuf; + llvm::raw_svector_ostream OS(SBuf); + OS << "Nullable pointer is passed to a callee that requires a non-null " + << ParamIdx << llvm::getOrdinalSuffix(ParamIdx) << " parameter"; + reportBugIfInvariantHolds(OS.str(), + ErrorKind::NullablePassedToNonnull, N, + Region, C, ArgExpr, /*SuppressPath=*/true); + return; + } + if (Filter.CheckNullableDereferenced && + Param->getType()->isReferenceType()) { + ExplodedNode *N = C.addTransition(State); + reportBugIfInvariantHolds("Nullable pointer is dereferenced", + ErrorKind::NullableDereferenced, N, Region, + C, ArgExpr, /*SuppressPath=*/true); + return; + } + continue; + } + // No tracked nullability yet. + if (ArgExprTypeLevelNullability != Nullability::Nullable) + continue; + State = State->set<NullabilityMap>( + Region, NullabilityState(ArgExprTypeLevelNullability, ArgExpr)); + } + if (State != OrigState) + C.addTransition(State); +} + +/// Suppress the nullability warnings for some functions. +void NullabilityChecker::checkPostCall(const CallEvent &Call, + CheckerContext &C) const { + auto Decl = Call.getDecl(); + if (!Decl) + return; + // ObjC Messages handles in a different callback. + if (Call.getKind() == CE_ObjCMessage) + return; + const FunctionType *FuncType = Decl->getFunctionType(); + if (!FuncType) + return; + QualType ReturnType = FuncType->getReturnType(); + if (!ReturnType->isAnyPointerType()) + return; + ProgramStateRef State = C.getState(); + if (State->get<InvariantViolated>()) + return; + + const MemRegion *Region = getTrackRegion(Call.getReturnValue()); + if (!Region) + return; + + // CG headers are misannotated. Do not warn for symbols that are the results + // of CG calls. + const SourceManager &SM = C.getSourceManager(); + StringRef FilePath = SM.getFilename(SM.getSpellingLoc(Decl->getBeginLoc())); + if (llvm::sys::path::filename(FilePath).startswith("CG")) { + State = State->set<NullabilityMap>(Region, Nullability::Contradicted); + C.addTransition(State); + return; + } + + const NullabilityState *TrackedNullability = + State->get<NullabilityMap>(Region); + + if (!TrackedNullability && + getNullabilityAnnotation(ReturnType) == Nullability::Nullable) { + State = State->set<NullabilityMap>(Region, Nullability::Nullable); + C.addTransition(State); + } +} + +static Nullability getReceiverNullability(const ObjCMethodCall &M, + ProgramStateRef State) { + if (M.isReceiverSelfOrSuper()) { + // For super and super class receivers we assume that the receiver is + // nonnull. + return Nullability::Nonnull; + } + // Otherwise look up nullability in the state. + SVal Receiver = M.getReceiverSVal(); + if (auto DefOrUnknown = Receiver.getAs<DefinedOrUnknownSVal>()) { + // If the receiver is constrained to be nonnull, assume that it is nonnull + // regardless of its type. + NullConstraint Nullness = getNullConstraint(*DefOrUnknown, State); + if (Nullness == NullConstraint::IsNotNull) + return Nullability::Nonnull; + } + auto ValueRegionSVal = Receiver.getAs<loc::MemRegionVal>(); + if (ValueRegionSVal) { + const MemRegion *SelfRegion = ValueRegionSVal->getRegion(); + assert(SelfRegion); + + const NullabilityState *TrackedSelfNullability = + State->get<NullabilityMap>(SelfRegion); + if (TrackedSelfNullability) + return TrackedSelfNullability->getValue(); + } + return Nullability::Unspecified; +} + +/// Calculate the nullability of the result of a message expr based on the +/// nullability of the receiver, the nullability of the return value, and the +/// constraints. +void NullabilityChecker::checkPostObjCMessage(const ObjCMethodCall &M, + CheckerContext &C) const { + auto Decl = M.getDecl(); + if (!Decl) + return; + QualType RetType = Decl->getReturnType(); + if (!RetType->isAnyPointerType()) + return; + + ProgramStateRef State = C.getState(); + if (State->get<InvariantViolated>()) + return; + + const MemRegion *ReturnRegion = getTrackRegion(M.getReturnValue()); + if (!ReturnRegion) + return; + + auto Interface = Decl->getClassInterface(); + auto Name = Interface ? Interface->getName() : ""; + // In order to reduce the noise in the diagnostics generated by this checker, + // some framework and programming style based heuristics are used. These + // heuristics are for Cocoa APIs which have NS prefix. + if (Name.startswith("NS")) { + // Developers rely on dynamic invariants such as an item should be available + // in a collection, or a collection is not empty often. Those invariants can + // not be inferred by any static analysis tool. To not to bother the users + // with too many false positives, every item retrieval function should be + // ignored for collections. The instance methods of dictionaries in Cocoa + // are either item retrieval related or not interesting nullability wise. + // Using this fact, to keep the code easier to read just ignore the return + // value of every instance method of dictionaries. + if (M.isInstanceMessage() && Name.contains("Dictionary")) { + State = + State->set<NullabilityMap>(ReturnRegion, Nullability::Contradicted); + C.addTransition(State); + return; + } + // For similar reasons ignore some methods of Cocoa arrays. + StringRef FirstSelectorSlot = M.getSelector().getNameForSlot(0); + if (Name.contains("Array") && + (FirstSelectorSlot == "firstObject" || + FirstSelectorSlot == "lastObject")) { + State = + State->set<NullabilityMap>(ReturnRegion, Nullability::Contradicted); + C.addTransition(State); + return; + } + + // Encoding related methods of string should not fail when lossless + // encodings are used. Using lossless encodings is so frequent that ignoring + // this class of methods reduced the emitted diagnostics by about 30% on + // some projects (and all of that was false positives). + if (Name.contains("String")) { + for (auto Param : M.parameters()) { + if (Param->getName() == "encoding") { + State = State->set<NullabilityMap>(ReturnRegion, + Nullability::Contradicted); + C.addTransition(State); + return; + } + } + } + } + + const ObjCMessageExpr *Message = M.getOriginExpr(); + Nullability SelfNullability = getReceiverNullability(M, State); + + const NullabilityState *NullabilityOfReturn = + State->get<NullabilityMap>(ReturnRegion); + + if (NullabilityOfReturn) { + // When we have a nullability tracked for the return value, the nullability + // of the expression will be the most nullable of the receiver and the + // return value. + Nullability RetValTracked = NullabilityOfReturn->getValue(); + Nullability ComputedNullab = + getMostNullable(RetValTracked, SelfNullability); + if (ComputedNullab != RetValTracked && + ComputedNullab != Nullability::Unspecified) { + const Stmt *NullabilitySource = + ComputedNullab == RetValTracked + ? NullabilityOfReturn->getNullabilitySource() + : Message->getInstanceReceiver(); + State = State->set<NullabilityMap>( + ReturnRegion, NullabilityState(ComputedNullab, NullabilitySource)); + C.addTransition(State); + } + return; + } + + // No tracked information. Use static type information for return value. + Nullability RetNullability = getNullabilityAnnotation(RetType); + + // Properties might be computed. For this reason the static analyzer creates a + // new symbol each time an unknown property is read. To avoid false pozitives + // do not treat unknown properties as nullable, even when they explicitly + // marked nullable. + if (M.getMessageKind() == OCM_PropertyAccess && !C.wasInlined) + RetNullability = Nullability::Nonnull; + + Nullability ComputedNullab = getMostNullable(RetNullability, SelfNullability); + if (ComputedNullab == Nullability::Nullable) { + const Stmt *NullabilitySource = ComputedNullab == RetNullability + ? Message + : Message->getInstanceReceiver(); + State = State->set<NullabilityMap>( + ReturnRegion, NullabilityState(ComputedNullab, NullabilitySource)); + C.addTransition(State); + } +} + +/// Explicit casts are trusted. If there is a disagreement in the nullability +/// annotations in the destination and the source or '0' is casted to nonnull +/// track the value as having contraditory nullability. This will allow users to +/// suppress warnings. +void NullabilityChecker::checkPostStmt(const ExplicitCastExpr *CE, + CheckerContext &C) const { + QualType OriginType = CE->getSubExpr()->getType(); + QualType DestType = CE->getType(); + if (!OriginType->isAnyPointerType()) + return; + if (!DestType->isAnyPointerType()) + return; + + ProgramStateRef State = C.getState(); + if (State->get<InvariantViolated>()) + return; + + Nullability DestNullability = getNullabilityAnnotation(DestType); + + // No explicit nullability in the destination type, so this cast does not + // change the nullability. + if (DestNullability == Nullability::Unspecified) + return; + + auto RegionSVal = C.getSVal(CE).getAs<DefinedOrUnknownSVal>(); + const MemRegion *Region = getTrackRegion(*RegionSVal); + if (!Region) + return; + + // When 0 is converted to nonnull mark it as contradicted. + if (DestNullability == Nullability::Nonnull) { + NullConstraint Nullness = getNullConstraint(*RegionSVal, State); + if (Nullness == NullConstraint::IsNull) { + State = State->set<NullabilityMap>(Region, Nullability::Contradicted); + C.addTransition(State); + return; + } + } + + const NullabilityState *TrackedNullability = + State->get<NullabilityMap>(Region); + + if (!TrackedNullability) { + if (DestNullability != Nullability::Nullable) + return; + State = State->set<NullabilityMap>(Region, + NullabilityState(DestNullability, CE)); + C.addTransition(State); + return; + } + + if (TrackedNullability->getValue() != DestNullability && + TrackedNullability->getValue() != Nullability::Contradicted) { + State = State->set<NullabilityMap>(Region, Nullability::Contradicted); + C.addTransition(State); + } +} + +/// For a given statement performing a bind, attempt to syntactically +/// match the expression resulting in the bound value. +static const Expr * matchValueExprForBind(const Stmt *S) { + // For `x = e` the value expression is the right-hand side. + if (auto *BinOp = dyn_cast<BinaryOperator>(S)) { + if (BinOp->getOpcode() == BO_Assign) + return BinOp->getRHS(); + } + + // For `int x = e` the value expression is the initializer. + if (auto *DS = dyn_cast<DeclStmt>(S)) { + if (DS->isSingleDecl()) { + auto *VD = dyn_cast<VarDecl>(DS->getSingleDecl()); + if (!VD) + return nullptr; + + if (const Expr *Init = VD->getInit()) + return Init; + } + } + + return nullptr; +} + +/// Returns true if \param S is a DeclStmt for a local variable that +/// ObjC automated reference counting initialized with zero. +static bool isARCNilInitializedLocal(CheckerContext &C, const Stmt *S) { + // We suppress diagnostics for ARC zero-initialized _Nonnull locals. This + // prevents false positives when a _Nonnull local variable cannot be + // initialized with an initialization expression: + // NSString * _Nonnull s; // no-warning + // @autoreleasepool { + // s = ... + // } + // + // FIXME: We should treat implicitly zero-initialized _Nonnull locals as + // uninitialized in Sema's UninitializedValues analysis to warn when a use of + // the zero-initialized definition will unexpectedly yield nil. + + // Locals are only zero-initialized when automated reference counting + // is turned on. + if (!C.getASTContext().getLangOpts().ObjCAutoRefCount) + return false; + + auto *DS = dyn_cast<DeclStmt>(S); + if (!DS || !DS->isSingleDecl()) + return false; + + auto *VD = dyn_cast<VarDecl>(DS->getSingleDecl()); + if (!VD) + return false; + + // Sema only zero-initializes locals with ObjCLifetimes. + if(!VD->getType().getQualifiers().hasObjCLifetime()) + return false; + + const Expr *Init = VD->getInit(); + assert(Init && "ObjC local under ARC without initializer"); + + // Return false if the local is explicitly initialized (e.g., with '= nil'). + if (!isa<ImplicitValueInitExpr>(Init)) + return false; + + return true; +} + +/// Propagate the nullability information through binds and warn when nullable +/// pointer or null symbol is assigned to a pointer with a nonnull type. +void NullabilityChecker::checkBind(SVal L, SVal V, const Stmt *S, + CheckerContext &C) const { + const TypedValueRegion *TVR = + dyn_cast_or_null<TypedValueRegion>(L.getAsRegion()); + if (!TVR) + return; + + QualType LocType = TVR->getValueType(); + if (!LocType->isAnyPointerType()) + return; + + ProgramStateRef State = C.getState(); + if (State->get<InvariantViolated>()) + return; + + auto ValDefOrUnknown = V.getAs<DefinedOrUnknownSVal>(); + if (!ValDefOrUnknown) + return; + + NullConstraint RhsNullness = getNullConstraint(*ValDefOrUnknown, State); + + Nullability ValNullability = Nullability::Unspecified; + if (SymbolRef Sym = ValDefOrUnknown->getAsSymbol()) + ValNullability = getNullabilityAnnotation(Sym->getType()); + + Nullability LocNullability = getNullabilityAnnotation(LocType); + + // If the type of the RHS expression is nonnull, don't warn. This + // enables explicit suppression with a cast to nonnull. + Nullability ValueExprTypeLevelNullability = Nullability::Unspecified; + const Expr *ValueExpr = matchValueExprForBind(S); + if (ValueExpr) { + ValueExprTypeLevelNullability = + getNullabilityAnnotation(lookThroughImplicitCasts(ValueExpr)->getType()); + } + + bool NullAssignedToNonNull = (LocNullability == Nullability::Nonnull && + RhsNullness == NullConstraint::IsNull); + if (Filter.CheckNullPassedToNonnull && + NullAssignedToNonNull && + ValNullability != Nullability::Nonnull && + ValueExprTypeLevelNullability != Nullability::Nonnull && + !isARCNilInitializedLocal(C, S)) { + static CheckerProgramPointTag Tag(this, "NullPassedToNonnull"); + ExplodedNode *N = C.generateErrorNode(State, &Tag); + if (!N) + return; + + + const Stmt *ValueStmt = S; + if (ValueExpr) + ValueStmt = ValueExpr; + + SmallString<256> SBuf; + llvm::raw_svector_ostream OS(SBuf); + OS << (LocType->isObjCObjectPointerType() ? "nil" : "Null"); + OS << " assigned to a pointer which is expected to have non-null value"; + reportBugIfInvariantHolds(OS.str(), + ErrorKind::NilAssignedToNonnull, N, nullptr, C, + ValueStmt); + return; + } + + // If null was returned from a non-null function, mark the nullability + // invariant as violated even if the diagnostic was suppressed. + if (NullAssignedToNonNull) { + State = State->set<InvariantViolated>(true); + C.addTransition(State); + return; + } + + // Intentionally missing case: '0' is bound to a reference. It is handled by + // the DereferenceChecker. + + const MemRegion *ValueRegion = getTrackRegion(*ValDefOrUnknown); + if (!ValueRegion) + return; + + const NullabilityState *TrackedNullability = + State->get<NullabilityMap>(ValueRegion); + + if (TrackedNullability) { + if (RhsNullness == NullConstraint::IsNotNull || + TrackedNullability->getValue() != Nullability::Nullable) + return; + if (Filter.CheckNullablePassedToNonnull && + LocNullability == Nullability::Nonnull) { + static CheckerProgramPointTag Tag(this, "NullablePassedToNonnull"); + ExplodedNode *N = C.addTransition(State, C.getPredecessor(), &Tag); + reportBugIfInvariantHolds("Nullable pointer is assigned to a pointer " + "which is expected to have non-null value", + ErrorKind::NullableAssignedToNonnull, N, + ValueRegion, C); + } + return; + } + + const auto *BinOp = dyn_cast<BinaryOperator>(S); + + if (ValNullability == Nullability::Nullable) { + // Trust the static information of the value more than the static + // information on the location. + const Stmt *NullabilitySource = BinOp ? BinOp->getRHS() : S; + State = State->set<NullabilityMap>( + ValueRegion, NullabilityState(ValNullability, NullabilitySource)); + C.addTransition(State); + return; + } + + if (LocNullability == Nullability::Nullable) { + const Stmt *NullabilitySource = BinOp ? BinOp->getLHS() : S; + State = State->set<NullabilityMap>( + ValueRegion, NullabilityState(LocNullability, NullabilitySource)); + C.addTransition(State); + } +} + +void NullabilityChecker::printState(raw_ostream &Out, ProgramStateRef State, + const char *NL, const char *Sep) const { + + NullabilityMapTy B = State->get<NullabilityMap>(); + + if (State->get<InvariantViolated>()) + Out << Sep << NL + << "Nullability invariant was violated, warnings suppressed." << NL; + + if (B.isEmpty()) + return; + + if (!State->get<InvariantViolated>()) + Out << Sep << NL; + + for (NullabilityMapTy::iterator I = B.begin(), E = B.end(); I != E; ++I) { + Out << I->first << " : "; + I->second.print(Out); + Out << NL; + } +} + +void ento::registerNullabilityBase(CheckerManager &mgr) { + mgr.registerChecker<NullabilityChecker>(); +} + +bool ento::shouldRegisterNullabilityBase(const LangOptions &LO) { + return true; +} + +#define REGISTER_CHECKER(name, trackingRequired) \ + void ento::register##name##Checker(CheckerManager &mgr) { \ + NullabilityChecker *checker = mgr.getChecker<NullabilityChecker>(); \ + checker->Filter.Check##name = true; \ + checker->Filter.CheckName##name = mgr.getCurrentCheckerName(); \ + checker->NeedTracking = checker->NeedTracking || trackingRequired; \ + checker->NoDiagnoseCallsToSystemHeaders = \ + checker->NoDiagnoseCallsToSystemHeaders || \ + mgr.getAnalyzerOptions().getCheckerBooleanOption( \ + checker, "NoDiagnoseCallsToSystemHeaders", true); \ + } \ + \ + bool ento::shouldRegister##name##Checker(const LangOptions &LO) { \ + return true; \ + } + +// The checks are likely to be turned on by default and it is possible to do +// them without tracking any nullability related information. As an optimization +// no nullability information will be tracked when only these two checks are +// enables. +REGISTER_CHECKER(NullPassedToNonnull, false) +REGISTER_CHECKER(NullReturnedFromNonnull, false) + +REGISTER_CHECKER(NullableDereferenced, true) +REGISTER_CHECKER(NullablePassedToNonnull, true) +REGISTER_CHECKER(NullableReturnedFromNonnull, true) |