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      1 //=- DirectIvarAssignment.cpp - Check rules on ObjC properties -*- 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 //  Check that Objective C properties are set with the setter, not though a
     11 //      direct assignment.
     12 //
     13 //  Two versions of a checker exist: one that checks all methods and the other
     14 //      that only checks the methods annotated with
     15 //      __attribute__((annotate("objc_no_direct_instance_variable_assignment")))
     16 //
     17 //  The checker does not warn about assignments to Ivars, annotated with
     18 //       __attribute__((objc_allow_direct_instance_variable_assignment"))). This
     19 //      annotation serves as a false positive suppression mechanism for the
     20 //      checker. The annotation is allowed on properties and Ivars.
     21 //
     22 //===----------------------------------------------------------------------===//
     23 
     24 #include "ClangSACheckers.h"
     25 #include "clang/AST/Attr.h"
     26 #include "clang/AST/DeclObjC.h"
     27 #include "clang/AST/StmtVisitor.h"
     28 #include "clang/StaticAnalyzer/Core/BugReporter/BugReporter.h"
     29 #include "clang/StaticAnalyzer/Core/Checker.h"
     30 #include "clang/StaticAnalyzer/Core/PathSensitive/AnalysisManager.h"
     31 #include "llvm/ADT/DenseMap.h"
     32 
     33 using namespace clang;
     34 using namespace ento;
     35 
     36 namespace {
     37 
     38 /// The default method filter, which is used to filter out the methods on which
     39 /// the check should not be performed.
     40 ///
     41 /// Checks for the init, dealloc, and any other functions that might be allowed
     42 /// to perform direct instance variable assignment based on their name.
     43 static bool DefaultMethodFilter(const ObjCMethodDecl *M) {
     44   return M->getMethodFamily() == OMF_init ||
     45          M->getMethodFamily() == OMF_dealloc ||
     46          M->getMethodFamily() == OMF_copy ||
     47          M->getMethodFamily() == OMF_mutableCopy ||
     48          M->getSelector().getNameForSlot(0).find("init") != StringRef::npos ||
     49          M->getSelector().getNameForSlot(0).find("Init") != StringRef::npos;
     50 }
     51 
     52 class DirectIvarAssignment :
     53   public Checker<check::ASTDecl<ObjCImplementationDecl> > {
     54 
     55   typedef llvm::DenseMap<const ObjCIvarDecl*,
     56                          const ObjCPropertyDecl*> IvarToPropertyMapTy;
     57 
     58   /// A helper class, which walks the AST and locates all assignments to ivars
     59   /// in the given function.
     60   class MethodCrawler : public ConstStmtVisitor<MethodCrawler> {
     61     const IvarToPropertyMapTy &IvarToPropMap;
     62     const ObjCMethodDecl *MD;
     63     const ObjCInterfaceDecl *InterfD;
     64     BugReporter &BR;
     65     const CheckerBase *Checker;
     66     LocationOrAnalysisDeclContext DCtx;
     67 
     68   public:
     69     MethodCrawler(const IvarToPropertyMapTy &InMap, const ObjCMethodDecl *InMD,
     70                   const ObjCInterfaceDecl *InID, BugReporter &InBR,
     71                   const CheckerBase *Checker, AnalysisDeclContext *InDCtx)
     72         : IvarToPropMap(InMap), MD(InMD), InterfD(InID), BR(InBR),
     73           Checker(Checker), DCtx(InDCtx) {}
     74 
     75     void VisitStmt(const Stmt *S) { VisitChildren(S); }
     76 
     77     void VisitBinaryOperator(const BinaryOperator *BO);
     78 
     79     void VisitChildren(const Stmt *S) {
     80       for (const Stmt *Child : S->children())
     81         if (Child)
     82           this->Visit(Child);
     83     }
     84   };
     85 
     86 public:
     87   bool (*ShouldSkipMethod)(const ObjCMethodDecl *);
     88 
     89   DirectIvarAssignment() : ShouldSkipMethod(&DefaultMethodFilter) {}
     90 
     91   void checkASTDecl(const ObjCImplementationDecl *D, AnalysisManager& Mgr,
     92                     BugReporter &BR) const;
     93 };
     94 
     95 static const ObjCIvarDecl *findPropertyBackingIvar(const ObjCPropertyDecl *PD,
     96                                                const ObjCInterfaceDecl *InterD,
     97                                                ASTContext &Ctx) {
     98   // Check for synthesized ivars.
     99   ObjCIvarDecl *ID = PD->getPropertyIvarDecl();
    100   if (ID)
    101     return ID;
    102 
    103   ObjCInterfaceDecl *NonConstInterD = const_cast<ObjCInterfaceDecl*>(InterD);
    104 
    105   // Check for existing "_PropName".
    106   ID = NonConstInterD->lookupInstanceVariable(PD->getDefaultSynthIvarName(Ctx));
    107   if (ID)
    108     return ID;
    109 
    110   // Check for existing "PropName".
    111   IdentifierInfo *PropIdent = PD->getIdentifier();
    112   ID = NonConstInterD->lookupInstanceVariable(PropIdent);
    113 
    114   return ID;
    115 }
    116 
    117 void DirectIvarAssignment::checkASTDecl(const ObjCImplementationDecl *D,
    118                                        AnalysisManager& Mgr,
    119                                        BugReporter &BR) const {
    120   const ObjCInterfaceDecl *InterD = D->getClassInterface();
    121 
    122 
    123   IvarToPropertyMapTy IvarToPropMap;
    124 
    125   // Find all properties for this class.
    126   for (const auto *PD : InterD->instance_properties()) {
    127     // Find the corresponding IVar.
    128     const ObjCIvarDecl *ID = findPropertyBackingIvar(PD, InterD,
    129                                                      Mgr.getASTContext());
    130 
    131     if (!ID)
    132       continue;
    133 
    134     // Store the IVar to property mapping.
    135     IvarToPropMap[ID] = PD;
    136   }
    137 
    138   if (IvarToPropMap.empty())
    139     return;
    140 
    141   for (const auto *M : D->instance_methods()) {
    142     AnalysisDeclContext *DCtx = Mgr.getAnalysisDeclContext(M);
    143 
    144     if ((*ShouldSkipMethod)(M))
    145       continue;
    146 
    147     const Stmt *Body = M->getBody();
    148     assert(Body);
    149 
    150     MethodCrawler MC(IvarToPropMap, M->getCanonicalDecl(), InterD, BR, this,
    151                      DCtx);
    152     MC.VisitStmt(Body);
    153   }
    154 }
    155 
    156 static bool isAnnotatedToAllowDirectAssignment(const Decl *D) {
    157   for (const auto *Ann : D->specific_attrs<AnnotateAttr>())
    158     if (Ann->getAnnotation() ==
    159         "objc_allow_direct_instance_variable_assignment")
    160       return true;
    161   return false;
    162 }
    163 
    164 void DirectIvarAssignment::MethodCrawler::VisitBinaryOperator(
    165                                                     const BinaryOperator *BO) {
    166   if (!BO->isAssignmentOp())
    167     return;
    168 
    169   const ObjCIvarRefExpr *IvarRef =
    170           dyn_cast<ObjCIvarRefExpr>(BO->getLHS()->IgnoreParenCasts());
    171 
    172   if (!IvarRef)
    173     return;
    174 
    175   if (const ObjCIvarDecl *D = IvarRef->getDecl()) {
    176     IvarToPropertyMapTy::const_iterator I = IvarToPropMap.find(D);
    177 
    178     if (I != IvarToPropMap.end()) {
    179       const ObjCPropertyDecl *PD = I->second;
    180       // Skip warnings on Ivars, annotated with
    181       // objc_allow_direct_instance_variable_assignment. This annotation serves
    182       // as a false positive suppression mechanism for the checker. The
    183       // annotation is allowed on properties and ivars.
    184       if (isAnnotatedToAllowDirectAssignment(PD) ||
    185           isAnnotatedToAllowDirectAssignment(D))
    186         return;
    187 
    188       ObjCMethodDecl *GetterMethod =
    189           InterfD->getInstanceMethod(PD->getGetterName());
    190       ObjCMethodDecl *SetterMethod =
    191           InterfD->getInstanceMethod(PD->getSetterName());
    192 
    193       if (SetterMethod && SetterMethod->getCanonicalDecl() == MD)
    194         return;
    195 
    196       if (GetterMethod && GetterMethod->getCanonicalDecl() == MD)
    197         return;
    198 
    199       BR.EmitBasicReport(
    200           MD, Checker, "Property access", categories::CoreFoundationObjectiveC,
    201           "Direct assignment to an instance variable backing a property; "
    202           "use the setter instead",
    203           PathDiagnosticLocation(IvarRef, BR.getSourceManager(), DCtx));
    204     }
    205   }
    206 }
    207 }
    208 
    209 // Register the checker that checks for direct accesses in all functions,
    210 // except for the initialization and copy routines.
    211 void ento::registerDirectIvarAssignment(CheckerManager &mgr) {
    212   mgr.registerChecker<DirectIvarAssignment>();
    213 }
    214 
    215 // Register the checker that checks for direct accesses in functions annotated
    216 // with __attribute__((annotate("objc_no_direct_instance_variable_assignment"))).
    217 static bool AttrFilter(const ObjCMethodDecl *M) {
    218   for (const auto *Ann : M->specific_attrs<AnnotateAttr>())
    219     if (Ann->getAnnotation() == "objc_no_direct_instance_variable_assignment")
    220       return false;
    221   return true;
    222 }
    223 
    224 void ento::registerDirectIvarAssignmentForAnnotatedFunctions(
    225     CheckerManager &mgr) {
    226   mgr.registerChecker<DirectIvarAssignment>()->ShouldSkipMethod = &AttrFilter;
    227 }
    228