1 //=== CastSizeChecker.cpp ---------------------------------------*- 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 // CastSizeChecker checks when casting a malloc'ed symbolic region to type T, 11 // whether the size of the symbolic region is a multiple of the size of T. 12 // 13 //===----------------------------------------------------------------------===// 14 #include "ClangSACheckers.h" 15 #include "clang/AST/CharUnits.h" 16 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h" 17 #include "clang/StaticAnalyzer/Core/Checker.h" 18 #include "clang/StaticAnalyzer/Core/CheckerManager.h" 19 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h" 20 21 using namespace clang; 22 using namespace ento; 23 24 namespace { 25 class CastSizeChecker : public Checker< check::PreStmt<CastExpr> > { 26 mutable OwningPtr<BuiltinBug> BT; 27 public: 28 void checkPreStmt(const CastExpr *CE, CheckerContext &C) const; 29 }; 30 } 31 32 /// Check if we are casting to a struct with a flexible array at the end. 33 /// \code 34 /// struct foo { 35 /// size_t len; 36 /// struct bar data[]; 37 /// }; 38 /// \endcode 39 /// or 40 /// \code 41 /// struct foo { 42 /// size_t len; 43 /// struct bar data[0]; 44 /// } 45 /// \endcode 46 /// In these cases it is also valid to allocate size of struct foo + a multiple 47 /// of struct bar. 48 static bool evenFlexibleArraySize(ASTContext &Ctx, CharUnits RegionSize, 49 CharUnits TypeSize, QualType ToPointeeTy) { 50 const RecordType *RT = ToPointeeTy->getAs<RecordType>(); 51 if (!RT) 52 return false; 53 54 const RecordDecl *RD = RT->getDecl(); 55 RecordDecl::field_iterator Iter(RD->field_begin()); 56 RecordDecl::field_iterator End(RD->field_end()); 57 const FieldDecl *Last = 0; 58 for (; Iter != End; ++Iter) 59 Last = *Iter; 60 assert(Last && "empty structs should already be handled"); 61 62 const Type *ElemType = Last->getType()->getArrayElementTypeNoTypeQual(); 63 CharUnits FlexSize; 64 if (const ConstantArrayType *ArrayTy = 65 Ctx.getAsConstantArrayType(Last->getType())) { 66 FlexSize = Ctx.getTypeSizeInChars(ElemType); 67 if (ArrayTy->getSize() == 1 && TypeSize > FlexSize) 68 TypeSize -= FlexSize; 69 else if (ArrayTy->getSize() != 0) 70 return false; 71 } else if (RD->hasFlexibleArrayMember()) { 72 FlexSize = Ctx.getTypeSizeInChars(ElemType); 73 } else { 74 return false; 75 } 76 77 if (FlexSize.isZero()) 78 return false; 79 80 CharUnits Left = RegionSize - TypeSize; 81 if (Left.isNegative()) 82 return false; 83 84 if (Left % FlexSize == 0) 85 return true; 86 87 return false; 88 } 89 90 void CastSizeChecker::checkPreStmt(const CastExpr *CE,CheckerContext &C) const { 91 const Expr *E = CE->getSubExpr(); 92 ASTContext &Ctx = C.getASTContext(); 93 QualType ToTy = Ctx.getCanonicalType(CE->getType()); 94 const PointerType *ToPTy = dyn_cast<PointerType>(ToTy.getTypePtr()); 95 96 if (!ToPTy) 97 return; 98 99 QualType ToPointeeTy = ToPTy->getPointeeType(); 100 101 // Only perform the check if 'ToPointeeTy' is a complete type. 102 if (ToPointeeTy->isIncompleteType()) 103 return; 104 105 ProgramStateRef state = C.getState(); 106 const MemRegion *R = state->getSVal(E, C.getLocationContext()).getAsRegion(); 107 if (R == 0) 108 return; 109 110 const SymbolicRegion *SR = dyn_cast<SymbolicRegion>(R); 111 if (SR == 0) 112 return; 113 114 SValBuilder &svalBuilder = C.getSValBuilder(); 115 SVal extent = SR->getExtent(svalBuilder); 116 const llvm::APSInt *extentInt = svalBuilder.getKnownValue(state, extent); 117 if (!extentInt) 118 return; 119 120 CharUnits regionSize = CharUnits::fromQuantity(extentInt->getSExtValue()); 121 CharUnits typeSize = C.getASTContext().getTypeSizeInChars(ToPointeeTy); 122 123 // Ignore void, and a few other un-sizeable types. 124 if (typeSize.isZero()) 125 return; 126 127 if (regionSize % typeSize == 0) 128 return; 129 130 if (evenFlexibleArraySize(Ctx, regionSize, typeSize, ToPointeeTy)) 131 return; 132 133 if (ExplodedNode *errorNode = C.generateSink()) { 134 if (!BT) 135 BT.reset(new BuiltinBug(this, "Cast region with wrong size.", 136 "Cast a region whose size is not a multiple" 137 " of the destination type size.")); 138 BugReport *R = new BugReport(*BT, BT->getDescription(), errorNode); 139 R->addRange(CE->getSourceRange()); 140 C.emitReport(R); 141 } 142 } 143 144 void ento::registerCastSizeChecker(CheckerManager &mgr) { 145 mgr.registerChecker<CastSizeChecker>(); 146 } 147