1 //=== CastSizeChecker.cpp ---------------------------------------*- C++ -*-===//
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
7 //===----------------------------------------------------------------------===//
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.
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"
20 using namespace clang;
24 class CastSizeChecker : public Checker< check::PreStmt<CastExpr> > {
25 mutable std::unique_ptr<BuiltinBug> BT;
28 void checkPreStmt(const CastExpr *CE, CheckerContext &C) const;
32 /// Check if we are casting to a struct with a flexible array at the end.
36 /// struct bar data[];
43 /// struct bar data[0];
46 /// In these cases it is also valid to allocate size of struct foo + a multiple
48 static bool evenFlexibleArraySize(ASTContext &Ctx, CharUnits RegionSize,
49 CharUnits TypeSize, QualType ToPointeeTy) {
50 const RecordType *RT = ToPointeeTy->getAs<RecordType>();
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)
60 assert(Last && "empty structs should already be handled");
62 const Type *ElemType = Last->getType()->getArrayElementTypeNoTypeQual();
64 if (const ConstantArrayType *ArrayTy =
65 Ctx.getAsConstantArrayType(Last->getType())) {
66 FlexSize = Ctx.getTypeSizeInChars(ElemType);
67 if (ArrayTy->getSize() == 1 && TypeSize > FlexSize)
69 else if (ArrayTy->getSize() != 0)
71 } else if (RD->hasFlexibleArrayMember()) {
72 FlexSize = Ctx.getTypeSizeInChars(ElemType);
77 if (FlexSize.isZero())
80 CharUnits Left = RegionSize - TypeSize;
81 if (Left.isNegative())
84 return Left % FlexSize == 0;
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());
96 QualType ToPointeeTy = ToPTy->getPointeeType();
98 // Only perform the check if 'ToPointeeTy' is a complete type.
99 if (ToPointeeTy->isIncompleteType())
102 ProgramStateRef state = C.getState();
103 const MemRegion *R = C.getSVal(E).getAsRegion();
107 const SymbolicRegion *SR = dyn_cast<SymbolicRegion>(R);
111 SValBuilder &svalBuilder = C.getSValBuilder();
112 SVal extent = SR->getExtent(svalBuilder);
113 const llvm::APSInt *extentInt = svalBuilder.getKnownValue(state, extent);
117 CharUnits regionSize = CharUnits::fromQuantity(extentInt->getSExtValue());
118 CharUnits typeSize = C.getASTContext().getTypeSizeInChars(ToPointeeTy);
120 // Ignore void, and a few other un-sizeable types.
121 if (typeSize.isZero())
124 if (regionSize % typeSize == 0)
127 if (evenFlexibleArraySize(Ctx, regionSize, typeSize, ToPointeeTy))
130 if (ExplodedNode *errorNode = C.generateErrorNode()) {
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 = llvm::make_unique<BugReport>(*BT, BT->getDescription(), errorNode);
136 R->addRange(CE->getSourceRange());
137 C.emitReport(std::move(R));
141 void ento::registerCastSizeChecker(CheckerManager &mgr) {
142 mgr.registerChecker<CastSizeChecker>();
145 bool ento::shouldRegisterCastSizeChecker(const LangOptions &LO) {
146 // PR31226: C++ is more complicated than what this checker currently supports.
147 // There are derived-to-base casts, there are different rules for 0-size
148 // structures, no flexible arrays, etc.
149 // FIXME: Disabled on C++ for now.
150 return !LO.CPlusPlus;