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