1 //=== CastSizeChecker.cpp ---------------------------------------*- C++ -*-===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // CastSizeChecker checks when casting a malloc'ed symbolic region to type T, 10 // whether the size of the symbolic region is a multiple of the size of T. 11 // 12 //===----------------------------------------------------------------------===// 13 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h" 14 #include "clang/AST/CharUnits.h" 15 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h" 16 #include "clang/StaticAnalyzer/Core/Checker.h" 17 #include "clang/StaticAnalyzer/Core/CheckerManager.h" 18 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h" 19 20 using namespace clang; 21 using namespace ento; 22 23 namespace { 24 class CastSizeChecker : public Checker< check::PreStmt<CastExpr> > { 25 mutable std::unique_ptr<BuiltinBug> BT; 26 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 = nullptr; 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 return Left % FlexSize == 0; 85 } 86 87 void CastSizeChecker::checkPreStmt(const CastExpr *CE,CheckerContext &C) const { 88 const Expr *E = CE->getSubExpr(); 89 ASTContext &Ctx = C.getASTContext(); 90 QualType ToTy = Ctx.getCanonicalType(CE->getType()); 91 const PointerType *ToPTy = dyn_cast<PointerType>(ToTy.getTypePtr()); 92 93 if (!ToPTy) 94 return; 95 96 QualType ToPointeeTy = ToPTy->getPointeeType(); 97 98 // Only perform the check if 'ToPointeeTy' is a complete type. 99 if (ToPointeeTy->isIncompleteType()) 100 return; 101 102 ProgramStateRef state = C.getState(); 103 const MemRegion *R = C.getSVal(E).getAsRegion(); 104 if (!R) 105 return; 106 107 const SymbolicRegion *SR = dyn_cast<SymbolicRegion>(R); 108 if (!SR) 109 return; 110 111 SValBuilder &svalBuilder = C.getSValBuilder(); 112 SVal extent = SR->getExtent(svalBuilder); 113 const llvm::APSInt *extentInt = svalBuilder.getKnownValue(state, extent); 114 if (!extentInt) 115 return; 116 117 CharUnits regionSize = CharUnits::fromQuantity(extentInt->getSExtValue()); 118 CharUnits typeSize = C.getASTContext().getTypeSizeInChars(ToPointeeTy); 119 120 // Ignore void, and a few other un-sizeable types. 121 if (typeSize.isZero()) 122 return; 123 124 if (regionSize % typeSize == 0) 125 return; 126 127 if (evenFlexibleArraySize(Ctx, regionSize, typeSize, ToPointeeTy)) 128 return; 129 130 if (ExplodedNode *errorNode = C.generateErrorNode()) { 131 if (!BT) 132 BT.reset(new BuiltinBug(this, "Cast region with wrong size.", 133 "Cast a region whose size is not a multiple" 134 " of the destination type size.")); 135 auto R = std::make_unique<PathSensitiveBugReport>(*BT, BT->getDescription(), 136 errorNode); 137 R->addRange(CE->getSourceRange()); 138 C.emitReport(std::move(R)); 139 } 140 } 141 142 void ento::registerCastSizeChecker(CheckerManager &mgr) { 143 mgr.registerChecker<CastSizeChecker>(); 144 } 145 146 bool ento::shouldRegisterCastSizeChecker(const LangOptions &LO) { 147 // PR31226: C++ is more complicated than what this checker currently supports. 148 // There are derived-to-base casts, there are different rules for 0-size 149 // structures, no flexible arrays, etc. 150 // FIXME: Disabled on C++ for now. 151 return !LO.CPlusPlus; 152 } 153