CastSizeChecker.cpp revision 651f13cea278ec967336033dd032faef0e9fc2ec 
1//=== CastSizeChecker.cpp ---------------------------------------*- 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// CastSizeChecker checks when casting a malloc'ed symbolic region to type T,
11// whether the size of the symbolic region is a multiple of the size of T.
12//
13//===----------------------------------------------------------------------===//
14#include "ClangSACheckers.h"
15#include "clang/AST/CharUnits.h"
16#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
17#include "clang/StaticAnalyzer/Core/Checker.h"
18#include "clang/StaticAnalyzer/Core/CheckerManager.h"
19#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
20
21using namespace clang;
22using namespace ento;
23
24namespace {
25class CastSizeChecker : public Checker< check::PreStmt<CastExpr> > {
26  mutable std::unique_ptr<BuiltinBug> BT;
27
28public:
29  void checkPreStmt(const CastExpr *CE, CheckerContext &C) const;
30};
31}
32
33/// Check if we are casting to a struct with a flexible array at the end.
34/// \code
35/// struct foo {
36///   size_t len;
37///   struct bar data[];
38/// };
39/// \endcode
40/// or
41/// \code
42/// struct foo {
43///   size_t len;
44///   struct bar data[0];
45/// }
46/// \endcode
47/// In these cases it is also valid to allocate size of struct foo + a multiple
48/// of struct bar.
49static bool evenFlexibleArraySize(ASTContext &Ctx, CharUnits RegionSize,
50                                  CharUnits TypeSize, QualType ToPointeeTy) {
51  const RecordType *RT = ToPointeeTy->getAs<RecordType>();
52  if (!RT)
53    return false;
54
55  const RecordDecl *RD = RT->getDecl();
56  RecordDecl::field_iterator Iter(RD->field_begin());
57  RecordDecl::field_iterator End(RD->field_end());
58  const FieldDecl *Last = 0;
59  for (; Iter != End; ++Iter)
60    Last = *Iter;
61  assert(Last && "empty structs should already be handled");
62
63  const Type *ElemType = Last->getType()->getArrayElementTypeNoTypeQual();
64  CharUnits FlexSize;
65  if (const ConstantArrayType *ArrayTy =
66        Ctx.getAsConstantArrayType(Last->getType())) {
67    FlexSize = Ctx.getTypeSizeInChars(ElemType);
68    if (ArrayTy->getSize() == 1 && TypeSize > FlexSize)
69      TypeSize -= FlexSize;
70    else if (ArrayTy->getSize() != 0)
71      return false;
72  } else if (RD->hasFlexibleArrayMember()) {
73    FlexSize = Ctx.getTypeSizeInChars(ElemType);
74  } else {
75    return false;
76  }
77
78  if (FlexSize.isZero())
79    return false;
80
81  CharUnits Left = RegionSize - TypeSize;
82  if (Left.isNegative())
83    return false;
84
85  if (Left % FlexSize == 0)
86    return true;
87
88  return false;
89}
90
91void CastSizeChecker::checkPreStmt(const CastExpr *CE,CheckerContext &C) const {
92  const Expr *E = CE->getSubExpr();
93  ASTContext &Ctx = C.getASTContext();
94  QualType ToTy = Ctx.getCanonicalType(CE->getType());
95  const PointerType *ToPTy = dyn_cast<PointerType>(ToTy.getTypePtr());
96
97  if (!ToPTy)
98    return;
99
100  QualType ToPointeeTy = ToPTy->getPointeeType();
101
102  // Only perform the check if 'ToPointeeTy' is a complete type.
103  if (ToPointeeTy->isIncompleteType())
104    return;
105
106  ProgramStateRef state = C.getState();
107  const MemRegion *R = state->getSVal(E, C.getLocationContext()).getAsRegion();
108  if (R == 0)
109    return;
110
111  const SymbolicRegion *SR = dyn_cast<SymbolicRegion>(R);
112  if (SR == 0)
113    return;
114
115  SValBuilder &svalBuilder = C.getSValBuilder();
116  SVal extent = SR->getExtent(svalBuilder);
117  const llvm::APSInt *extentInt = svalBuilder.getKnownValue(state, extent);
118  if (!extentInt)
119    return;
120
121  CharUnits regionSize = CharUnits::fromQuantity(extentInt->getSExtValue());
122  CharUnits typeSize = C.getASTContext().getTypeSizeInChars(ToPointeeTy);
123
124  // Ignore void, and a few other un-sizeable types.
125  if (typeSize.isZero())
126    return;
127
128  if (regionSize % typeSize == 0)
129    return;
130
131  if (evenFlexibleArraySize(Ctx, regionSize, typeSize, ToPointeeTy))
132    return;
133
134  if (ExplodedNode *errorNode = C.generateSink()) {
135    if (!BT)
136      BT.reset(new BuiltinBug(this, "Cast region with wrong size.",
137                                    "Cast a region whose size is not a multiple"
138                                    " of the destination type size."));
139    BugReport *R = new BugReport(*BT, BT->getDescription(), errorNode);
140    R->addRange(CE->getSourceRange());
141    C.emitReport(R);
142  }
143}
144
145void ento::registerCastSizeChecker(CheckerManager &mgr) {
146  mgr.registerChecker<CastSizeChecker>();
147}
148