1 // MallocSizeofChecker.cpp - Check for dubious malloc arguments ---*- C++ -*-=//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // Reports inconsistencies between the casted type of the return value of a
11 // malloc/calloc/realloc call and the operand of any sizeof expressions
12 // contained within its argument(s).
13 //
14 //===----------------------------------------------------------------------===//
15 
16 #include "ClangSACheckers.h"
17 #include "clang/AST/StmtVisitor.h"
18 #include "clang/AST/TypeLoc.h"
19 #include "clang/StaticAnalyzer/Core/BugReporter/BugReporter.h"
20 #include "clang/StaticAnalyzer/Core/Checker.h"
21 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
22 #include "clang/StaticAnalyzer/Core/PathSensitive/AnalysisManager.h"
23 #include "llvm/ADT/SmallString.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 
CallRecord__anon4d425d760111::CastedAllocFinder::CallRecord45     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 
CastedAllocFinder(ASTContext * Ctx)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 
VisitChild(ExprParent Parent,const Stmt * S)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 
VisitChildren(const Stmt * S)67   void VisitChildren(const Stmt *S) {
68     for (Stmt::const_child_iterator I = S->child_begin(), E = S->child_end();
69          I!=E; ++I)
70       if (const Stmt *child = *I)
71         VisitChild(S, child);
72   }
73 
VisitCastExpr(const CastExpr * E)74   TypeCallPair VisitCastExpr(const CastExpr *E) {
75     return Visit(E->getSubExpr());
76   }
77 
VisitExplicitCastExpr(const ExplicitCastExpr * E)78   TypeCallPair VisitExplicitCastExpr(const ExplicitCastExpr *E) {
79     return TypeCallPair(E->getTypeInfoAsWritten(),
80                         Visit(E->getSubExpr()).second);
81   }
82 
VisitParenExpr(const ParenExpr * E)83   TypeCallPair VisitParenExpr(const ParenExpr *E) {
84     return Visit(E->getSubExpr());
85   }
86 
VisitStmt(const Stmt * S)87   TypeCallPair VisitStmt(const Stmt *S) {
88     VisitChildren(S);
89     return TypeCallPair();
90   }
91 
VisitCallExpr(const CallExpr * E)92   TypeCallPair VisitCallExpr(const CallExpr *E) {
93     VisitChildren(E);
94     const FunctionDecl *FD = E->getDirectCallee();
95     if (FD) {
96       IdentifierInfo *II = FD->getIdentifier();
97       if (II == II_malloc || II == II_calloc || II == II_realloc)
98         return TypeCallPair((const TypeSourceInfo *)nullptr, E);
99     }
100     return TypeCallPair();
101   }
102 
VisitDeclStmt(const DeclStmt * S)103   TypeCallPair VisitDeclStmt(const DeclStmt *S) {
104     for (const auto *I : S->decls())
105       if (const VarDecl *VD = dyn_cast<VarDecl>(I))
106         if (const Expr *Init = VD->getInit())
107           VisitChild(VD, Init);
108     return TypeCallPair();
109   }
110 };
111 
112 class SizeofFinder : public ConstStmtVisitor<SizeofFinder> {
113 public:
114   std::vector<const UnaryExprOrTypeTraitExpr *> Sizeofs;
115 
VisitBinMul(const BinaryOperator * E)116   void VisitBinMul(const BinaryOperator *E) {
117     Visit(E->getLHS());
118     Visit(E->getRHS());
119   }
120 
VisitImplicitCastExpr(const ImplicitCastExpr * E)121   void VisitImplicitCastExpr(const ImplicitCastExpr *E) {
122     return Visit(E->getSubExpr());
123   }
124 
VisitParenExpr(const ParenExpr * E)125   void VisitParenExpr(const ParenExpr *E) {
126     return Visit(E->getSubExpr());
127   }
128 
VisitUnaryExprOrTypeTraitExpr(const UnaryExprOrTypeTraitExpr * E)129   void VisitUnaryExprOrTypeTraitExpr(const UnaryExprOrTypeTraitExpr *E) {
130     if (E->getKind() != UETT_SizeOf)
131       return;
132 
133     Sizeofs.push_back(E);
134   }
135 };
136 
137 // Determine if the pointee and sizeof types are compatible.  Here
138 // we ignore constness of pointer types.
typesCompatible(ASTContext & C,QualType A,QualType B)139 static bool typesCompatible(ASTContext &C, QualType A, QualType B) {
140   // sizeof(void*) is compatible with any other pointer.
141   if (B->isVoidPointerType() && A->getAs<PointerType>())
142     return true;
143 
144   while (true) {
145     A = A.getCanonicalType();
146     B = B.getCanonicalType();
147 
148     if (A.getTypePtr() == B.getTypePtr())
149       return true;
150 
151     if (const PointerType *ptrA = A->getAs<PointerType>())
152       if (const PointerType *ptrB = B->getAs<PointerType>()) {
153         A = ptrA->getPointeeType();
154         B = ptrB->getPointeeType();
155         continue;
156       }
157 
158     break;
159   }
160 
161   return false;
162 }
163 
compatibleWithArrayType(ASTContext & C,QualType PT,QualType T)164 static bool compatibleWithArrayType(ASTContext &C, QualType PT, QualType T) {
165   // Ex: 'int a[10][2]' is compatible with 'int', 'int[2]', 'int[10][2]'.
166   while (const ArrayType *AT = T->getAsArrayTypeUnsafe()) {
167     QualType ElemType = AT->getElementType();
168     if (typesCompatible(C, PT, AT->getElementType()))
169       return true;
170     T = ElemType;
171   }
172 
173   return false;
174 }
175 
176 class MallocSizeofChecker : public Checker<check::ASTCodeBody> {
177 public:
checkASTCodeBody(const Decl * D,AnalysisManager & mgr,BugReporter & BR) const178   void checkASTCodeBody(const Decl *D, AnalysisManager& mgr,
179                         BugReporter &BR) const {
180     AnalysisDeclContext *ADC = mgr.getAnalysisDeclContext(D);
181     CastedAllocFinder Finder(&BR.getContext());
182     Finder.Visit(D->getBody());
183     for (CastedAllocFinder::CallVec::iterator i = Finder.Calls.begin(),
184          e = Finder.Calls.end(); i != e; ++i) {
185       QualType CastedType = i->CastedExpr->getType();
186       if (!CastedType->isPointerType())
187         continue;
188       QualType PointeeType = CastedType->getAs<PointerType>()->getPointeeType();
189       if (PointeeType->isVoidType())
190         continue;
191 
192       for (CallExpr::const_arg_iterator ai = i->AllocCall->arg_begin(),
193            ae = i->AllocCall->arg_end(); ai != ae; ++ai) {
194         if (!(*ai)->getType()->isIntegralOrUnscopedEnumerationType())
195           continue;
196 
197         SizeofFinder SFinder;
198         SFinder.Visit(*ai);
199         if (SFinder.Sizeofs.size() != 1)
200           continue;
201 
202         QualType SizeofType = SFinder.Sizeofs[0]->getTypeOfArgument();
203 
204         if (typesCompatible(BR.getContext(), PointeeType, SizeofType))
205           continue;
206 
207         // If the argument to sizeof is an array, the result could be a
208         // pointer to any array element.
209         if (compatibleWithArrayType(BR.getContext(), PointeeType, SizeofType))
210           continue;
211 
212         const TypeSourceInfo *TSI = nullptr;
213         if (i->CastedExprParent.is<const VarDecl *>()) {
214           TSI =
215               i->CastedExprParent.get<const VarDecl *>()->getTypeSourceInfo();
216         } else {
217           TSI = i->ExplicitCastType;
218         }
219 
220         SmallString<64> buf;
221         llvm::raw_svector_ostream OS(buf);
222 
223         OS << "Result of ";
224         const FunctionDecl *Callee = i->AllocCall->getDirectCallee();
225         if (Callee && Callee->getIdentifier())
226           OS << '\'' << Callee->getIdentifier()->getName() << '\'';
227         else
228           OS << "call";
229         OS << " is converted to a pointer of type '"
230             << PointeeType.getAsString() << "', which is incompatible with "
231             << "sizeof operand type '" << SizeofType.getAsString() << "'";
232         SmallVector<SourceRange, 4> Ranges;
233         Ranges.push_back(i->AllocCall->getCallee()->getSourceRange());
234         Ranges.push_back(SFinder.Sizeofs[0]->getSourceRange());
235         if (TSI)
236           Ranges.push_back(TSI->getTypeLoc().getSourceRange());
237 
238         PathDiagnosticLocation L =
239             PathDiagnosticLocation::createBegin(i->AllocCall->getCallee(),
240                 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 
registerMallocSizeofChecker(CheckerManager & mgr)251 void ento::registerMallocSizeofChecker(CheckerManager &mgr) {
252   mgr.registerChecker<MallocSizeofChecker>();
253 }
254