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
21 using namespace clang;
22 using namespace ento;
23
24 namespace {
25 class CastSizeChecker : public Checker< check::PreStmt<CastExpr> > {
26 mutable std::unique_ptr<BuiltinBug> BT;
27
28 public:
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.
evenFlexibleArraySize(ASTContext & Ctx,CharUnits RegionSize,CharUnits TypeSize,QualType ToPointeeTy)49 static 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 = nullptr;
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
checkPreStmt(const CastExpr * CE,CheckerContext & C) const91 void 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)
109 return;
110
111 const SymbolicRegion *SR = dyn_cast<SymbolicRegion>(R);
112 if (!SR)
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
registerCastSizeChecker(CheckerManager & mgr)145 void ento::registerCastSizeChecker(CheckerManager &mgr) {
146 mgr.registerChecker<CastSizeChecker>();
147 }
148