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
CallRecord__anonf7730cc40111::CastedAllocFinder::CallRecord44 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
CastedAllocFinder(ASTContext * Ctx)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
VisitChild(ExprParent Parent,const Stmt * S)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
VisitChildren(const Stmt * S)66 void VisitChildren(const Stmt *S) {
67 for (const Stmt *Child : S->children())
68 if (Child)
69 VisitChild(S, Child);
70 }
71
VisitCastExpr(const CastExpr * E)72 TypeCallPair VisitCastExpr(const CastExpr *E) {
73 return Visit(E->getSubExpr());
74 }
75
VisitExplicitCastExpr(const ExplicitCastExpr * E)76 TypeCallPair VisitExplicitCastExpr(const ExplicitCastExpr *E) {
77 return TypeCallPair(E->getTypeInfoAsWritten(),
78 Visit(E->getSubExpr()).second);
79 }
80
VisitParenExpr(const ParenExpr * E)81 TypeCallPair VisitParenExpr(const ParenExpr *E) {
82 return Visit(E->getSubExpr());
83 }
84
VisitStmt(const Stmt * S)85 TypeCallPair VisitStmt(const Stmt *S) {
86 VisitChildren(S);
87 return TypeCallPair();
88 }
89
VisitCallExpr(const CallExpr * E)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
VisitDeclStmt(const DeclStmt * S)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
VisitBinMul(const BinaryOperator * E)114 void VisitBinMul(const BinaryOperator *E) {
115 Visit(E->getLHS());
116 Visit(E->getRHS());
117 }
118
VisitImplicitCastExpr(const ImplicitCastExpr * E)119 void VisitImplicitCastExpr(const ImplicitCastExpr *E) {
120 return Visit(E->getSubExpr());
121 }
122
VisitParenExpr(const ParenExpr * E)123 void VisitParenExpr(const ParenExpr *E) {
124 return Visit(E->getSubExpr());
125 }
126
VisitUnaryExprOrTypeTraitExpr(const UnaryExprOrTypeTraitExpr * E)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.
typesCompatible(ASTContext & C,QualType A,QualType B)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 // sizeof(pointer type) is compatible with void*
143 if (A->isVoidPointerType() && B->getAs<PointerType>())
144 return true;
145
146 while (true) {
147 A = A.getCanonicalType();
148 B = B.getCanonicalType();
149
150 if (A.getTypePtr() == B.getTypePtr())
151 return true;
152
153 if (const PointerType *ptrA = A->getAs<PointerType>())
154 if (const PointerType *ptrB = B->getAs<PointerType>()) {
155 A = ptrA->getPointeeType();
156 B = ptrB->getPointeeType();
157 continue;
158 }
159
160 break;
161 }
162
163 return false;
164 }
165
compatibleWithArrayType(ASTContext & C,QualType PT,QualType T)166 static bool compatibleWithArrayType(ASTContext &C, QualType PT, QualType T) {
167 // Ex: 'int a[10][2]' is compatible with 'int', 'int[2]', 'int[10][2]'.
168 while (const ArrayType *AT = T->getAsArrayTypeUnsafe()) {
169 QualType ElemType = AT->getElementType();
170 if (typesCompatible(C, PT, AT->getElementType()))
171 return true;
172 T = ElemType;
173 }
174
175 return false;
176 }
177
178 class MallocSizeofChecker : public Checker<check::ASTCodeBody> {
179 public:
checkASTCodeBody(const Decl * D,AnalysisManager & mgr,BugReporter & BR) const180 void checkASTCodeBody(const Decl *D, AnalysisManager& mgr,
181 BugReporter &BR) const {
182 AnalysisDeclContext *ADC = mgr.getAnalysisDeclContext(D);
183 CastedAllocFinder Finder(&BR.getContext());
184 Finder.Visit(D->getBody());
185 for (CastedAllocFinder::CallVec::iterator i = Finder.Calls.begin(),
186 e = Finder.Calls.end(); i != e; ++i) {
187 QualType CastedType = i->CastedExpr->getType();
188 if (!CastedType->isPointerType())
189 continue;
190 QualType PointeeType = CastedType->getPointeeType();
191 if (PointeeType->isVoidType())
192 continue;
193
194 for (CallExpr::const_arg_iterator ai = i->AllocCall->arg_begin(),
195 ae = i->AllocCall->arg_end(); ai != ae; ++ai) {
196 if (!(*ai)->getType()->isIntegralOrUnscopedEnumerationType())
197 continue;
198
199 SizeofFinder SFinder;
200 SFinder.Visit(*ai);
201 if (SFinder.Sizeofs.size() != 1)
202 continue;
203
204 QualType SizeofType = SFinder.Sizeofs[0]->getTypeOfArgument();
205
206 if (typesCompatible(BR.getContext(), PointeeType, SizeofType))
207 continue;
208
209 // If the argument to sizeof is an array, the result could be a
210 // pointer to any array element.
211 if (compatibleWithArrayType(BR.getContext(), PointeeType, SizeofType))
212 continue;
213
214 const TypeSourceInfo *TSI = nullptr;
215 if (i->CastedExprParent.is<const VarDecl *>()) {
216 TSI =
217 i->CastedExprParent.get<const VarDecl *>()->getTypeSourceInfo();
218 } else {
219 TSI = i->ExplicitCastType;
220 }
221
222 SmallString<64> buf;
223 llvm::raw_svector_ostream OS(buf);
224
225 OS << "Result of ";
226 const FunctionDecl *Callee = i->AllocCall->getDirectCallee();
227 if (Callee && Callee->getIdentifier())
228 OS << '\'' << Callee->getIdentifier()->getName() << '\'';
229 else
230 OS << "call";
231 OS << " is converted to a pointer of type '"
232 << PointeeType.getAsString() << "', which is incompatible with "
233 << "sizeof operand type '" << SizeofType.getAsString() << "'";
234 SmallVector<SourceRange, 4> Ranges;
235 Ranges.push_back(i->AllocCall->getCallee()->getSourceRange());
236 Ranges.push_back(SFinder.Sizeofs[0]->getSourceRange());
237 if (TSI)
238 Ranges.push_back(TSI->getTypeLoc().getSourceRange());
239
240 PathDiagnosticLocation L =
241 PathDiagnosticLocation::createBegin(i->AllocCall->getCallee(),
242 BR.getSourceManager(), ADC);
243
244 BR.EmitBasicReport(D, this, "Allocator sizeof operand mismatch",
245 categories::UnixAPI, OS.str(), L, Ranges);
246 }
247 }
248 }
249 };
250
251 }
252
registerMallocSizeofChecker(CheckerManager & mgr)253 void ento::registerMallocSizeofChecker(CheckerManager &mgr) {
254 mgr.registerChecker<MallocSizeofChecker>();
255 }
256
shouldRegisterMallocSizeofChecker(const CheckerManager & mgr)257 bool ento::shouldRegisterMallocSizeofChecker(const CheckerManager &mgr) {
258 return true;
259 }
260