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