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 (Stmt::const_child_iterator I = S->child_begin(), E = S->child_end();
69         I!=E; ++I)
70      if (const Stmt *child = *I)
71        VisitChild(S, child);
72  }
73
74  TypeCallPair VisitCastExpr(const CastExpr *E) {
75    return Visit(E->getSubExpr());
76  }
77
78  TypeCallPair VisitExplicitCastExpr(const ExplicitCastExpr *E) {
79    return TypeCallPair(E->getTypeInfoAsWritten(),
80                        Visit(E->getSubExpr()).second);
81  }
82
83  TypeCallPair VisitParenExpr(const ParenExpr *E) {
84    return Visit(E->getSubExpr());
85  }
86
87  TypeCallPair VisitStmt(const Stmt *S) {
88    VisitChildren(S);
89    return TypeCallPair();
90  }
91
92  TypeCallPair VisitCallExpr(const CallExpr *E) {
93    VisitChildren(E);
94    const FunctionDecl *FD = E->getDirectCallee();
95    if (FD) {
96      IdentifierInfo *II = FD->getIdentifier();
97      if (II == II_malloc || II == II_calloc || II == II_realloc)
98        return TypeCallPair((const TypeSourceInfo *)nullptr, E);
99    }
100    return TypeCallPair();
101  }
102
103  TypeCallPair VisitDeclStmt(const DeclStmt *S) {
104    for (const auto *I : S->decls())
105      if (const VarDecl *VD = dyn_cast<VarDecl>(I))
106        if (const Expr *Init = VD->getInit())
107          VisitChild(VD, Init);
108    return TypeCallPair();
109  }
110};
111
112class SizeofFinder : public ConstStmtVisitor<SizeofFinder> {
113public:
114  std::vector<const UnaryExprOrTypeTraitExpr *> Sizeofs;
115
116  void VisitBinMul(const BinaryOperator *E) {
117    Visit(E->getLHS());
118    Visit(E->getRHS());
119  }
120
121  void VisitImplicitCastExpr(const ImplicitCastExpr *E) {
122    return Visit(E->getSubExpr());
123  }
124
125  void VisitParenExpr(const ParenExpr *E) {
126    return Visit(E->getSubExpr());
127  }
128
129  void VisitUnaryExprOrTypeTraitExpr(const UnaryExprOrTypeTraitExpr *E) {
130    if (E->getKind() != UETT_SizeOf)
131      return;
132
133    Sizeofs.push_back(E);
134  }
135};
136
137// Determine if the pointee and sizeof types are compatible.  Here
138// we ignore constness of pointer types.
139static bool typesCompatible(ASTContext &C, QualType A, QualType B) {
140  while (true) {
141    A = A.getCanonicalType();
142    B = B.getCanonicalType();
143
144    if (A.getTypePtr() == B.getTypePtr())
145      return true;
146
147    if (const PointerType *ptrA = A->getAs<PointerType>())
148      if (const PointerType *ptrB = B->getAs<PointerType>()) {
149        A = ptrA->getPointeeType();
150        B = ptrB->getPointeeType();
151        continue;
152      }
153
154    break;
155  }
156
157  return false;
158}
159
160static bool compatibleWithArrayType(ASTContext &C, QualType PT, QualType T) {
161  // Ex: 'int a[10][2]' is compatible with 'int', 'int[2]', 'int[10][2]'.
162  while (const ArrayType *AT = T->getAsArrayTypeUnsafe()) {
163    QualType ElemType = AT->getElementType();
164    if (typesCompatible(C, PT, AT->getElementType()))
165      return true;
166    T = ElemType;
167  }
168
169  return false;
170}
171
172class MallocSizeofChecker : public Checker<check::ASTCodeBody> {
173public:
174  void checkASTCodeBody(const Decl *D, AnalysisManager& mgr,
175                        BugReporter &BR) const {
176    AnalysisDeclContext *ADC = mgr.getAnalysisDeclContext(D);
177    CastedAllocFinder Finder(&BR.getContext());
178    Finder.Visit(D->getBody());
179    for (CastedAllocFinder::CallVec::iterator i = Finder.Calls.begin(),
180         e = Finder.Calls.end(); i != e; ++i) {
181      QualType CastedType = i->CastedExpr->getType();
182      if (!CastedType->isPointerType())
183        continue;
184      QualType PointeeType = CastedType->getAs<PointerType>()->getPointeeType();
185      if (PointeeType->isVoidType())
186        continue;
187
188      for (CallExpr::const_arg_iterator ai = i->AllocCall->arg_begin(),
189           ae = i->AllocCall->arg_end(); ai != ae; ++ai) {
190        if (!(*ai)->getType()->isIntegralOrUnscopedEnumerationType())
191          continue;
192
193        SizeofFinder SFinder;
194        SFinder.Visit(*ai);
195        if (SFinder.Sizeofs.size() != 1)
196          continue;
197
198        QualType SizeofType = SFinder.Sizeofs[0]->getTypeOfArgument();
199
200        if (typesCompatible(BR.getContext(), PointeeType, SizeofType))
201          continue;
202
203        // If the argument to sizeof is an array, the result could be a
204        // pointer to any array element.
205        if (compatibleWithArrayType(BR.getContext(), PointeeType, SizeofType))
206          continue;
207
208        const TypeSourceInfo *TSI = nullptr;
209        if (i->CastedExprParent.is<const VarDecl *>()) {
210          TSI =
211              i->CastedExprParent.get<const VarDecl *>()->getTypeSourceInfo();
212        } else {
213          TSI = i->ExplicitCastType;
214        }
215
216        SmallString<64> buf;
217        llvm::raw_svector_ostream OS(buf);
218
219        OS << "Result of ";
220        const FunctionDecl *Callee = i->AllocCall->getDirectCallee();
221        if (Callee && Callee->getIdentifier())
222          OS << '\'' << Callee->getIdentifier()->getName() << '\'';
223        else
224          OS << "call";
225        OS << " is converted to a pointer of type '"
226            << PointeeType.getAsString() << "', which is incompatible with "
227            << "sizeof operand type '" << SizeofType.getAsString() << "'";
228        SmallVector<SourceRange, 4> Ranges;
229        Ranges.push_back(i->AllocCall->getCallee()->getSourceRange());
230        Ranges.push_back(SFinder.Sizeofs[0]->getSourceRange());
231        if (TSI)
232          Ranges.push_back(TSI->getTypeLoc().getSourceRange());
233
234        PathDiagnosticLocation L =
235            PathDiagnosticLocation::createBegin(i->AllocCall->getCallee(),
236                BR.getSourceManager(), ADC);
237
238        BR.EmitBasicReport(D, this, "Allocator sizeof operand mismatch",
239                           categories::UnixAPI, OS.str(), L, Ranges);
240      }
241    }
242  }
243};
244
245}
246
247void ento::registerMallocSizeofChecker(CheckerManager &mgr) {
248  mgr.registerChecker<MallocSizeofChecker>();
249}
250