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
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("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
111class SizeofFinder : public ConstStmtVisitor<SizeofFinder> {
112public:
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.
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  while (true) {
144    A = A.getCanonicalType();
145    B = B.getCanonicalType();
146
147    if (A.getTypePtr() == B.getTypePtr())
148      return true;
149
150    if (const PointerType *ptrA = A->getAs<PointerType>())
151      if (const PointerType *ptrB = B->getAs<PointerType>()) {
152        A = ptrA->getPointeeType();
153        B = ptrB->getPointeeType();
154        continue;
155      }
156
157    break;
158  }
159
160  return false;
161}
162
163static bool compatibleWithArrayType(ASTContext &C, QualType PT, QualType T) {
164  // Ex: 'int a[10][2]' is compatible with 'int', 'int[2]', 'int[10][2]'.
165  while (const ArrayType *AT = T->getAsArrayTypeUnsafe()) {
166    QualType ElemType = AT->getElementType();
167    if (typesCompatible(C, PT, AT->getElementType()))
168      return true;
169    T = ElemType;
170  }
171
172  return false;
173}
174
175class MallocSizeofChecker : public Checker<check::ASTCodeBody> {
176public:
177  void checkASTCodeBody(const Decl *D, AnalysisManager& mgr,
178                        BugReporter &BR) const {
179    AnalysisDeclContext *ADC = mgr.getAnalysisDeclContext(D);
180    CastedAllocFinder Finder(&BR.getContext());
181    Finder.Visit(D->getBody());
182    for (CastedAllocFinder::CallVec::iterator i = Finder.Calls.begin(),
183         e = Finder.Calls.end(); i != e; ++i) {
184      QualType CastedType = i->CastedExpr->getType();
185      if (!CastedType->isPointerType())
186        continue;
187      QualType PointeeType = CastedType->getAs<PointerType>()->getPointeeType();
188      if (PointeeType->isVoidType())
189        continue;
190
191      for (CallExpr::const_arg_iterator ai = i->AllocCall->arg_begin(),
192           ae = i->AllocCall->arg_end(); ai != ae; ++ai) {
193        if (!(*ai)->getType()->isIntegralOrUnscopedEnumerationType())
194          continue;
195
196        SizeofFinder SFinder;
197        SFinder.Visit(*ai);
198        if (SFinder.Sizeofs.size() != 1)
199          continue;
200
201        QualType SizeofType = SFinder.Sizeofs[0]->getTypeOfArgument();
202
203        if (typesCompatible(BR.getContext(), PointeeType, SizeofType))
204          continue;
205
206        // If the argument to sizeof is an array, the result could be a
207        // pointer to any array element.
208        if (compatibleWithArrayType(BR.getContext(), PointeeType, SizeofType))
209          continue;
210
211        const TypeSourceInfo *TSI = nullptr;
212        if (i->CastedExprParent.is<const VarDecl *>()) {
213          TSI =
214              i->CastedExprParent.get<const VarDecl *>()->getTypeSourceInfo();
215        } else {
216          TSI = i->ExplicitCastType;
217        }
218
219        SmallString<64> buf;
220        llvm::raw_svector_ostream OS(buf);
221
222        OS << "Result of ";
223        const FunctionDecl *Callee = i->AllocCall->getDirectCallee();
224        if (Callee && Callee->getIdentifier())
225          OS << '\'' << Callee->getIdentifier()->getName() << '\'';
226        else
227          OS << "call";
228        OS << " is converted to a pointer of type '"
229            << PointeeType.getAsString() << "', which is incompatible with "
230            << "sizeof operand type '" << SizeofType.getAsString() << "'";
231        SmallVector<SourceRange, 4> Ranges;
232        Ranges.push_back(i->AllocCall->getCallee()->getSourceRange());
233        Ranges.push_back(SFinder.Sizeofs[0]->getSourceRange());
234        if (TSI)
235          Ranges.push_back(TSI->getTypeLoc().getSourceRange());
236
237        PathDiagnosticLocation L =
238            PathDiagnosticLocation::createBegin(i->AllocCall->getCallee(),
239                BR.getSourceManager(), ADC);
240
241        BR.EmitBasicReport(D, this, "Allocator sizeof operand mismatch",
242                           categories::UnixAPI, OS.str(), L, Ranges);
243      }
244    }
245  }
246};
247
248}
249
250void ento::registerMallocSizeofChecker(CheckerManager &mgr) {
251  mgr.registerChecker<MallocSizeofChecker>();
252}
253