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
26using namespace clang;
27using namespace ento;
28
29namespace {
30
31typedef std::pair<const TypeSourceInfo *, const CallExpr *> TypeCallPair;
32typedef llvm::PointerUnion<const Stmt *, const VarDecl *> ExprParent;
33
34class CastedAllocFinder
35 : public ConstStmtVisitor<CastedAllocFinder, TypeCallPair> {
36 IdentifierInfo *II_malloc, *II_calloc, *II_realloc;
37
38public:
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(Name: "malloc")),
57 II_calloc(&Ctx->Idents.get(Name: "calloc")),
58 II_realloc(&Ctx->Idents.get(Name: "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(x: CallRecord(Parent, cast<Expr>(Val: 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(Parent: S, S: Child);
71 }
72
73 TypeCallPair VisitCastExpr(const CastExpr *E) {
74 return Visit(S: E->getSubExpr());
75 }
76
77 TypeCallPair VisitExplicitCastExpr(const ExplicitCastExpr *E) {
78 return TypeCallPair(E->getTypeInfoAsWritten(),
79 Visit(S: E->getSubExpr()).second);
80 }
81
82 TypeCallPair VisitParenExpr(const ParenExpr *E) {
83 return Visit(S: 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(S: 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>(Val: I))
105 if (const Expr *Init = VD->getInit())
106 VisitChild(Parent: VD, S: Init);
107 return TypeCallPair();
108 }
109};
110
111class SizeofFinder : public ConstStmtVisitor<SizeofFinder> {
112public:
113 std::vector<const UnaryExprOrTypeTraitExpr *> Sizeofs;
114
115 void VisitBinMul(const BinaryOperator *E) {
116 Visit(S: E->getLHS());
117 Visit(S: E->getRHS());
118 }
119
120 void VisitImplicitCastExpr(const ImplicitCastExpr *E) {
121 return Visit(S: E->getSubExpr());
122 }
123
124 void VisitParenExpr(const ParenExpr *E) {
125 return Visit(S: E->getSubExpr());
126 }
127
128 void VisitUnaryExprOrTypeTraitExpr(const UnaryExprOrTypeTraitExpr *E) {
129 if (E->getKind() != UETT_SizeOf)
130 return;
131
132 Sizeofs.push_back(x: E);
133 }
134};
135
136// Determine if the pointee and sizeof types are compatible. Here
137// we ignore constness of pointer types.
138static 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
167static 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, A: PT, B: AT->getElementType()))
172 return true;
173 T = ElemType;
174 }
175
176 return false;
177}
178
179class MallocSizeofChecker : public Checker<check::ASTCodeBody> {
180public:
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(S: 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(S: Arg);
200 if (SFinder.Sizeofs.size() != 1)
201 continue;
202
203 QualType SizeofType = SFinder.Sizeofs[0]->getTypeOfArgument();
204
205 if (typesCompatible(C&: BR.getContext(), A: PointeeType, B: 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(C&: BR.getContext(), PT: PointeeType, T: 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(Elt: CallRec.AllocCall->getCallee()->getSourceRange());
235 Ranges.push_back(Elt: SFinder.Sizeofs[0]->getSourceRange());
236 if (TSI)
237 Ranges.push_back(Elt: TSI->getTypeLoc().getSourceRange());
238
239 PathDiagnosticLocation L = PathDiagnosticLocation::createBegin(
240 S: CallRec.AllocCall->getCallee(), SM: BR.getSourceManager(), LAC: ADC);
241
242 BR.EmitBasicReport(DeclWithIssue: D, Checker: this, BugName: "Allocator sizeof operand mismatch",
243 BugCategory: categories::UnixAPI, BugStr: OS.str(), Loc: L, Ranges);
244 }
245 }
246 }
247};
248
249}
250
251void ento::registerMallocSizeofChecker(CheckerManager &mgr) {
252 mgr.registerChecker<MallocSizeofChecker>();
253}
254
255bool ento::shouldRegisterMallocSizeofChecker(const CheckerManager &mgr) {
256 return true;
257}
258