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 27using namespace clang; 28using namespace ento; 29 30namespace { 31class 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 50public: 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. 64REGISTER_MAP_WITH_PROGRAMSTATE(ArraySizeMap, SymbolRef, DefinedSVal) 65 66void 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 84void 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 107void 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 153ProgramStateRef 154ObjCContainersChecker::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. 170void ento::registerObjCContainersChecker(CheckerManager &mgr) { 171 mgr.registerChecker<ObjCContainersChecker>(); 172} 173