1 // MallocSizeofChecker.cpp - Check for dubious malloc arguments ---*- 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 // Reports inconsistencies between the casted type of the return value of a 10 // malloc/calloc/realloc call and the operand of any sizeof expressions 11 // contained within its argument(s). 12 // 13 //===----------------------------------------------------------------------===// 14 15 #include "clang/AST/StmtVisitor.h" 16 #include "clang/AST/TypeLoc.h" 17 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h" 18 #include "clang/StaticAnalyzer/Core/BugReporter/BugReporter.h" 19 #include "clang/StaticAnalyzer/Core/Checker.h" 20 #include "clang/StaticAnalyzer/Core/CheckerManager.h" 21 #include "clang/StaticAnalyzer/Core/PathSensitive/AnalysisManager.h" 22 #include "llvm/ADT/SmallString.h" 23 #include "llvm/ADT/iterator_range.h" 24 #include "llvm/Support/raw_ostream.h" 25 26 using namespace clang; 27 using namespace ento; 28 29 namespace { 30 31 typedef std::pair<const TypeSourceInfo *, const CallExpr *> TypeCallPair; 32 typedef llvm::PointerUnion<const Stmt *, const VarDecl *> ExprParent; 33 34 class CastedAllocFinder 35 : public ConstStmtVisitor<CastedAllocFinder, TypeCallPair> { 36 IdentifierInfo *II_malloc, *II_calloc, *II_realloc; 37 38 public: 39 struct CallRecord { 40 ExprParent CastedExprParent; 41 const Expr *CastedExpr; 42 const TypeSourceInfo *ExplicitCastType; 43 const CallExpr *AllocCall; 44 45 CallRecord(ExprParent CastedExprParent, const Expr *CastedExpr, 46 const TypeSourceInfo *ExplicitCastType, 47 const CallExpr *AllocCall) 48 : CastedExprParent(CastedExprParent), CastedExpr(CastedExpr), 49 ExplicitCastType(ExplicitCastType), AllocCall(AllocCall) {} 50 }; 51 52 typedef std::vector<CallRecord> CallVec; 53 CallVec Calls; 54 55 CastedAllocFinder(ASTContext *Ctx) : 56 II_malloc(&Ctx->Idents.get("malloc")), 57 II_calloc(&Ctx->Idents.get("calloc")), 58 II_realloc(&Ctx->Idents.get("realloc")) {} 59 60 void VisitChild(ExprParent Parent, const Stmt *S) { 61 TypeCallPair AllocCall = Visit(S); 62 if (AllocCall.second && AllocCall.second != S) 63 Calls.push_back(CallRecord(Parent, cast<Expr>(S), AllocCall.first, 64 AllocCall.second)); 65 } 66 67 void VisitChildren(const Stmt *S) { 68 for (const Stmt *Child : S->children()) 69 if (Child) 70 VisitChild(S, Child); 71 } 72 73 TypeCallPair VisitCastExpr(const CastExpr *E) { 74 return Visit(E->getSubExpr()); 75 } 76 77 TypeCallPair VisitExplicitCastExpr(const ExplicitCastExpr *E) { 78 return TypeCallPair(E->getTypeInfoAsWritten(), 79 Visit(E->getSubExpr()).second); 80 } 81 82 TypeCallPair VisitParenExpr(const ParenExpr *E) { 83 return Visit(E->getSubExpr()); 84 } 85 86 TypeCallPair VisitStmt(const Stmt *S) { 87 VisitChildren(S); 88 return TypeCallPair(); 89 } 90 91 TypeCallPair VisitCallExpr(const CallExpr *E) { 92 VisitChildren(E); 93 const FunctionDecl *FD = E->getDirectCallee(); 94 if (FD) { 95 IdentifierInfo *II = FD->getIdentifier(); 96 if (II == II_malloc || II == II_calloc || II == II_realloc) 97 return TypeCallPair((const TypeSourceInfo *)nullptr, E); 98 } 99 return TypeCallPair(); 100 } 101 102 TypeCallPair VisitDeclStmt(const DeclStmt *S) { 103 for (const auto *I : S->decls()) 104 if (const VarDecl *VD = dyn_cast<VarDecl>(I)) 105 if (const Expr *Init = VD->getInit()) 106 VisitChild(VD, Init); 107 return TypeCallPair(); 108 } 109 }; 110 111 class SizeofFinder : public ConstStmtVisitor<SizeofFinder> { 112 public: 113 std::vector<const UnaryExprOrTypeTraitExpr *> Sizeofs; 114 115 void VisitBinMul(const BinaryOperator *E) { 116 Visit(E->getLHS()); 117 Visit(E->getRHS()); 118 } 119 120 void VisitImplicitCastExpr(const ImplicitCastExpr *E) { 121 return Visit(E->getSubExpr()); 122 } 123 124 void VisitParenExpr(const ParenExpr *E) { 125 return Visit(E->getSubExpr()); 126 } 127 128 void VisitUnaryExprOrTypeTraitExpr(const UnaryExprOrTypeTraitExpr *E) { 129 if (E->getKind() != UETT_SizeOf) 130 return; 131 132 Sizeofs.push_back(E); 133 } 134 }; 135 136 // Determine if the pointee and sizeof types are compatible. Here 137 // we ignore constness of pointer types. 138 static bool typesCompatible(ASTContext &C, QualType A, QualType B) { 139 // sizeof(void*) is compatible with any other pointer. 140 if (B->isVoidPointerType() && A->getAs<PointerType>()) 141 return true; 142 143 // sizeof(pointer type) is compatible with void* 144 if (A->isVoidPointerType() && B->getAs<PointerType>()) 145 return true; 146 147 while (true) { 148 A = A.getCanonicalType(); 149 B = B.getCanonicalType(); 150 151 if (A.getTypePtr() == B.getTypePtr()) 152 return true; 153 154 if (const PointerType *ptrA = A->getAs<PointerType>()) 155 if (const PointerType *ptrB = B->getAs<PointerType>()) { 156 A = ptrA->getPointeeType(); 157 B = ptrB->getPointeeType(); 158 continue; 159 } 160 161 break; 162 } 163 164 return false; 165 } 166 167 static bool compatibleWithArrayType(ASTContext &C, QualType PT, QualType T) { 168 // Ex: 'int a[10][2]' is compatible with 'int', 'int[2]', 'int[10][2]'. 169 while (const ArrayType *AT = T->getAsArrayTypeUnsafe()) { 170 QualType ElemType = AT->getElementType(); 171 if (typesCompatible(C, PT, AT->getElementType())) 172 return true; 173 T = ElemType; 174 } 175 176 return false; 177 } 178 179 class MallocSizeofChecker : public Checker<check::ASTCodeBody> { 180 public: 181 void checkASTCodeBody(const Decl *D, AnalysisManager& mgr, 182 BugReporter &BR) const { 183 AnalysisDeclContext *ADC = mgr.getAnalysisDeclContext(D); 184 CastedAllocFinder Finder(&BR.getContext()); 185 Finder.Visit(D->getBody()); 186 for (const auto &CallRec : Finder.Calls) { 187 QualType CastedType = CallRec.CastedExpr->getType(); 188 if (!CastedType->isPointerType()) 189 continue; 190 QualType PointeeType = CastedType->getPointeeType(); 191 if (PointeeType->isVoidType()) 192 continue; 193 194 for (const Expr *Arg : CallRec.AllocCall->arguments()) { 195 if (!Arg->getType()->isIntegralOrUnscopedEnumerationType()) 196 continue; 197 198 SizeofFinder SFinder; 199 SFinder.Visit(Arg); 200 if (SFinder.Sizeofs.size() != 1) 201 continue; 202 203 QualType SizeofType = SFinder.Sizeofs[0]->getTypeOfArgument(); 204 205 if (typesCompatible(BR.getContext(), PointeeType, SizeofType)) 206 continue; 207 208 // If the argument to sizeof is an array, the result could be a 209 // pointer to any array element. 210 if (compatibleWithArrayType(BR.getContext(), PointeeType, SizeofType)) 211 continue; 212 213 const TypeSourceInfo *TSI = nullptr; 214 if (CallRec.CastedExprParent.is<const VarDecl *>()) { 215 TSI = CallRec.CastedExprParent.get<const VarDecl *>() 216 ->getTypeSourceInfo(); 217 } else { 218 TSI = CallRec.ExplicitCastType; 219 } 220 221 SmallString<64> buf; 222 llvm::raw_svector_ostream OS(buf); 223 224 OS << "Result of "; 225 const FunctionDecl *Callee = CallRec.AllocCall->getDirectCallee(); 226 if (Callee && Callee->getIdentifier()) 227 OS << '\'' << Callee->getIdentifier()->getName() << '\''; 228 else 229 OS << "call"; 230 OS << " is converted to a pointer of type '" << PointeeType 231 << "', which is incompatible with " 232 << "sizeof operand type '" << SizeofType << "'"; 233 SmallVector<SourceRange, 4> Ranges; 234 Ranges.push_back(CallRec.AllocCall->getCallee()->getSourceRange()); 235 Ranges.push_back(SFinder.Sizeofs[0]->getSourceRange()); 236 if (TSI) 237 Ranges.push_back(TSI->getTypeLoc().getSourceRange()); 238 239 PathDiagnosticLocation L = PathDiagnosticLocation::createBegin( 240 CallRec.AllocCall->getCallee(), BR.getSourceManager(), ADC); 241 242 BR.EmitBasicReport(D, this, "Allocator sizeof operand mismatch", 243 categories::UnixAPI, OS.str(), L, Ranges); 244 } 245 } 246 } 247 }; 248 249 } 250 251 void ento::registerMallocSizeofChecker(CheckerManager &mgr) { 252 mgr.registerChecker<MallocSizeofChecker>(); 253 } 254 255 bool ento::shouldRegisterMallocSizeofChecker(const CheckerManager &mgr) { 256 return true; 257 } 258