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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   mutable OwningPtr<BugType> BT;
     34   inline void initBugType() const {
     35     if (!BT)
     36       BT.reset(new BugType("CFArray API",
     37                            categories::CoreFoundationObjectiveC));
     38   }
     39 
     40   inline SymbolRef getArraySym(const Expr *E, CheckerContext &C) const {
     41     SVal ArrayRef = C.getState()->getSVal(E, C.getLocationContext());
     42     SymbolRef ArraySym = ArrayRef.getAsSymbol();
     43     return ArraySym;
     44   }
     45 
     46   void addSizeInfo(const Expr *Array, const Expr *Size,
     47                    CheckerContext &C) const;
     48 
     49 public:
     50   /// A tag to id this checker.
     51   static void *getTag() { static int Tag; return &Tag; }
     52 
     53   void checkPostStmt(const CallExpr *CE, CheckerContext &C) const;
     54   void checkPreStmt(const CallExpr *CE, CheckerContext &C) const;
     55 };
     56 } // end anonymous namespace
     57 
     58 // ProgramState trait - a map from array symbol to its state.
     59 REGISTER_MAP_WITH_PROGRAMSTATE(ArraySizeMap, SymbolRef, DefinedSVal)
     60 
     61 void ObjCContainersChecker::addSizeInfo(const Expr *Array, const Expr *Size,
     62                                         CheckerContext &C) const {
     63   ProgramStateRef State = C.getState();
     64   SVal SizeV = State->getSVal(Size, C.getLocationContext());
     65   // Undefined is reported by another checker.
     66   if (SizeV.isUnknownOrUndef())
     67     return;
     68 
     69   // Get the ArrayRef symbol.
     70   SVal ArrayRef = State->getSVal(Array, C.getLocationContext());
     71   SymbolRef ArraySym = ArrayRef.getAsSymbol();
     72   if (!ArraySym)
     73     return;
     74 
     75   C.addTransition(
     76       State->set<ArraySizeMap>(ArraySym, SizeV.castAs<DefinedSVal>()));
     77   return;
     78 }
     79 
     80 void ObjCContainersChecker::checkPostStmt(const CallExpr *CE,
     81                                           CheckerContext &C) const {
     82   StringRef Name = C.getCalleeName(CE);
     83   if (Name.empty() || CE->getNumArgs() < 1)
     84     return;
     85 
     86   // Add array size information to the state.
     87   if (Name.equals("CFArrayCreate")) {
     88     if (CE->getNumArgs() < 3)
     89       return;
     90     // Note, we can visit the Create method in the post-visit because
     91     // the CFIndex parameter is passed in by value and will not be invalidated
     92     // by the call.
     93     addSizeInfo(CE, CE->getArg(2), C);
     94     return;
     95   }
     96 
     97   if (Name.equals("CFArrayGetCount")) {
     98     addSizeInfo(CE->getArg(0), CE, C);
     99     return;
    100   }
    101 }
    102 
    103 void ObjCContainersChecker::checkPreStmt(const CallExpr *CE,
    104                                          CheckerContext &C) const {
    105   StringRef Name = C.getCalleeName(CE);
    106   if (Name.empty() || CE->getNumArgs() < 2)
    107     return;
    108 
    109   // Check the array access.
    110   if (Name.equals("CFArrayGetValueAtIndex")) {
    111     ProgramStateRef State = C.getState();
    112     // Retrieve the size.
    113     // Find out if we saw this array symbol before and have information about it.
    114     const Expr *ArrayExpr = CE->getArg(0);
    115     SymbolRef ArraySym = getArraySym(ArrayExpr, C);
    116     if (!ArraySym)
    117       return;
    118 
    119     const DefinedSVal *Size = State->get<ArraySizeMap>(ArraySym);
    120 
    121     if (!Size)
    122       return;
    123 
    124     // Get the index.
    125     const Expr *IdxExpr = CE->getArg(1);
    126     SVal IdxVal = State->getSVal(IdxExpr, C.getLocationContext());
    127     if (IdxVal.isUnknownOrUndef())
    128       return;
    129     DefinedSVal Idx = IdxVal.castAs<DefinedSVal>();
    130 
    131     // Now, check if 'Idx in [0, Size-1]'.
    132     const QualType T = IdxExpr->getType();
    133     ProgramStateRef StInBound = State->assumeInBound(Idx, *Size, true, T);
    134     ProgramStateRef StOutBound = State->assumeInBound(Idx, *Size, false, T);
    135     if (StOutBound && !StInBound) {
    136       ExplodedNode *N = C.generateSink(StOutBound);
    137       if (!N)
    138         return;
    139       initBugType();
    140       BugReport *R = new BugReport(*BT, "Index is out of bounds", N);
    141       R->addRange(IdxExpr->getSourceRange());
    142       C.emitReport(R);
    143       return;
    144     }
    145   }
    146 }
    147 
    148 /// Register checker.
    149 void ento::registerObjCContainersChecker(CheckerManager &mgr) {
    150   mgr.registerChecker<ObjCContainersChecker>();
    151 }
    152