MallocSizeofChecker.cpp revision 360784 
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
25using namespace clang;
26using namespace ento;
27
28namespace {
29
30typedef std::pair<const TypeSourceInfo *, const CallExpr *> TypeCallPair;
31typedef llvm::PointerUnion<const Stmt *, const VarDecl *> ExprParent;
32
33class CastedAllocFinder
34  : public ConstStmtVisitor<CastedAllocFinder, TypeCallPair> {
35  IdentifierInfo *II_malloc, *II_calloc, *II_realloc;
36
37public:
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
110class SizeofFinder : public ConstStmtVisitor<SizeofFinder> {
111public:
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.
137static 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
162static 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
174class MallocSizeofChecker : public Checker<check::ASTCodeBody> {
175public:
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
249void ento::registerMallocSizeofChecker(CheckerManager &mgr) {
250  mgr.registerChecker<MallocSizeofChecker>();
251}
252
253bool ento::shouldRegisterMallocSizeofChecker(const LangOptions &LO) {
254  return true;
255}
256