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      1 //== ObjCContainersChecker.cpp - Path sensitive checker for CFArray *- 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 // Performs path sensitive checks of Core Foundation static containers like
     11 // CFArray.
     12 // 1) Check for buffer overflows:
     13 //      In CFArrayGetArrayAtIndex( myArray, index), if the index is outside the
     14 //      index space of theArray (0 to N-1 inclusive (where N is the count of
     15 //      theArray), the behavior is undefined.
     16 //
     17 //===----------------------------------------------------------------------===//
     18 
     19 #include "ClangSACheckers.h"
     20 #include "clang/AST/ParentMap.h"
     21 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
     22 #include "clang/StaticAnalyzer/Core/Checker.h"
     23 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
     24 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
     25 #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramStateTrait.h"
     26 
     27 using namespace clang;
     28 using namespace ento;
     29 
     30 namespace {
     31 class ObjCContainersChecker : public Checker< check::PreStmt<CallExpr>,
     32                                              check::PostStmt<CallExpr>,
     33                                              check::PointerEscape> {
     34   mutable std::unique_ptr<BugType> BT;
     35   inline void initBugType() const {
     36     if (!BT)
     37       BT.reset(new BugType(this, "CFArray API",
     38                            categories::CoreFoundationObjectiveC));
     39   }
     40 
     41   inline SymbolRef getArraySym(const Expr *E, CheckerContext &C) const {
     42     SVal ArrayRef = C.getState()->getSVal(E, C.getLocationContext());
     43     SymbolRef ArraySym = ArrayRef.getAsSymbol();
     44     return ArraySym;
     45   }
     46 
     47   void addSizeInfo(const Expr *Array, const Expr *Size,
     48                    CheckerContext &C) const;
     49 
     50 public:
     51   /// A tag to id this checker.
     52   static void *getTag() { static int Tag; return &Tag; }
     53 
     54   void checkPostStmt(const CallExpr *CE, CheckerContext &C) const;
     55   void checkPreStmt(const CallExpr *CE, CheckerContext &C) const;
     56   ProgramStateRef checkPointerEscape(ProgramStateRef State,
     57                                      const InvalidatedSymbols &Escaped,
     58                                      const CallEvent *Call,
     59                                      PointerEscapeKind Kind) const;
     60 };
     61 } // end anonymous namespace
     62 
     63 // ProgramState trait - a map from array symbol to its state.
     64 REGISTER_MAP_WITH_PROGRAMSTATE(ArraySizeMap, SymbolRef, DefinedSVal)
     65 
     66 void ObjCContainersChecker::addSizeInfo(const Expr *Array, const Expr *Size,
     67                                         CheckerContext &C) const {
     68   ProgramStateRef State = C.getState();
     69   SVal SizeV = State->getSVal(Size, C.getLocationContext());
     70   // Undefined is reported by another checker.
     71   if (SizeV.isUnknownOrUndef())
     72     return;
     73 
     74   // Get the ArrayRef symbol.
     75   SVal ArrayRef = State->getSVal(Array, C.getLocationContext());
     76   SymbolRef ArraySym = ArrayRef.getAsSymbol();
     77   if (!ArraySym)
     78     return;
     79 
     80   C.addTransition(
     81       State->set<ArraySizeMap>(ArraySym, SizeV.castAs<DefinedSVal>()));
     82 }
     83 
     84 void ObjCContainersChecker::checkPostStmt(const CallExpr *CE,
     85                                           CheckerContext &C) const {
     86   StringRef Name = C.getCalleeName(CE);
     87   if (Name.empty() || CE->getNumArgs() < 1)
     88     return;
     89 
     90   // Add array size information to the state.
     91   if (Name.equals("CFArrayCreate")) {
     92     if (CE->getNumArgs() < 3)
     93       return;
     94     // Note, we can visit the Create method in the post-visit because
     95     // the CFIndex parameter is passed in by value and will not be invalidated
     96     // by the call.
     97     addSizeInfo(CE, CE->getArg(2), C);
     98     return;
     99   }
    100 
    101   if (Name.equals("CFArrayGetCount")) {
    102     addSizeInfo(CE->getArg(0), CE, C);
    103     return;
    104   }
    105 }
    106 
    107 void ObjCContainersChecker::checkPreStmt(const CallExpr *CE,
    108                                          CheckerContext &C) const {
    109   StringRef Name = C.getCalleeName(CE);
    110   if (Name.empty() || CE->getNumArgs() < 2)
    111     return;
    112 
    113   // Check the array access.
    114   if (Name.equals("CFArrayGetValueAtIndex")) {
    115     ProgramStateRef State = C.getState();
    116     // Retrieve the size.
    117     // Find out if we saw this array symbol before and have information about
    118     // it.
    119     const Expr *ArrayExpr = CE->getArg(0);
    120     SymbolRef ArraySym = getArraySym(ArrayExpr, C);
    121     if (!ArraySym)
    122       return;
    123 
    124     const DefinedSVal *Size = State->get<ArraySizeMap>(ArraySym);
    125 
    126     if (!Size)
    127       return;
    128 
    129     // Get the index.
    130     const Expr *IdxExpr = CE->getArg(1);
    131     SVal IdxVal = State->getSVal(IdxExpr, C.getLocationContext());
    132     if (IdxVal.isUnknownOrUndef())
    133       return;
    134     DefinedSVal Idx = IdxVal.castAs<DefinedSVal>();
    135 
    136     // Now, check if 'Idx in [0, Size-1]'.
    137     const QualType T = IdxExpr->getType();
    138     ProgramStateRef StInBound = State->assumeInBound(Idx, *Size, true, T);
    139     ProgramStateRef StOutBound = State->assumeInBound(Idx, *Size, false, T);
    140     if (StOutBound && !StInBound) {
    141       ExplodedNode *N = C.generateErrorNode(StOutBound);
    142       if (!N)
    143         return;
    144       initBugType();
    145       auto R = llvm::make_unique<BugReport>(*BT, "Index is out of bounds", N);
    146       R->addRange(IdxExpr->getSourceRange());
    147       C.emitReport(std::move(R));
    148       return;
    149     }
    150   }
    151 }
    152 
    153 ProgramStateRef
    154 ObjCContainersChecker::checkPointerEscape(ProgramStateRef State,
    155                                           const InvalidatedSymbols &Escaped,
    156                                           const CallEvent *Call,
    157                                           PointerEscapeKind Kind) const {
    158   for (const auto &Sym : Escaped) {
    159     // When a symbol for a mutable array escapes, we can't reason precisely
    160     // about its size any more -- so remove it from the map.
    161     // Note that we aren't notified here when a CFMutableArrayRef escapes as a
    162     // CFArrayRef. This is because CFArrayRef is typedef'd as a pointer to a
    163     // const-qualified type.
    164     State = State->remove<ArraySizeMap>(Sym);
    165   }
    166   return State;
    167 }
    168 
    169 /// Register checker.
    170 void ento::registerObjCContainersChecker(CheckerManager &mgr) {
    171   mgr.registerChecker<ObjCContainersChecker>();
    172 }
    173