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