1 //=== VLASizeChecker.cpp - Undefined dereference checker --------*- 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 // This defines VLASizeChecker, a builtin check in ExprEngine that 11 // performs checks for declaration of VLA of undefined or zero size. 12 // In addition, VLASizeChecker is responsible for defining the extent 13 // of the MemRegion that represents a VLA. 14 // 15 //===----------------------------------------------------------------------===// 16 17 #include "ClangSACheckers.h" 18 #include "clang/AST/CharUnits.h" 19 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h" 20 #include "clang/StaticAnalyzer/Core/Checker.h" 21 #include "clang/StaticAnalyzer/Core/CheckerManager.h" 22 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h" 23 #include "llvm/ADT/STLExtras.h" 24 #include "llvm/ADT/SmallString.h" 25 #include "llvm/Support/raw_ostream.h" 26 27 using namespace clang; 28 using namespace ento; 29 30 namespace { 31 class VLASizeChecker : public Checker< check::PreStmt<DeclStmt> > { 32 mutable OwningPtr<BugType> BT; 33 enum VLASize_Kind { VLA_Garbage, VLA_Zero, VLA_Tainted }; 34 35 void reportBug(VLASize_Kind Kind, 36 const Expr *SizeE, 37 ProgramStateRef State, 38 CheckerContext &C) const; 39 public: 40 void checkPreStmt(const DeclStmt *DS, CheckerContext &C) const; 41 }; 42 } // end anonymous namespace 43 44 void VLASizeChecker::reportBug(VLASize_Kind Kind, 45 const Expr *SizeE, 46 ProgramStateRef State, 47 CheckerContext &C) const { 48 // Generate an error node. 49 ExplodedNode *N = C.generateSink(State); 50 if (!N) 51 return; 52 53 if (!BT) 54 BT.reset(new BuiltinBug("Dangerous variable-length array (VLA) declaration")); 55 56 SmallString<256> buf; 57 llvm::raw_svector_ostream os(buf); 58 os << "Declared variable-length array (VLA) "; 59 switch (Kind) { 60 case VLA_Garbage: 61 os << "uses a garbage value as its size"; 62 break; 63 case VLA_Zero: 64 os << "has zero size"; 65 break; 66 case VLA_Tainted: 67 os << "has tainted size"; 68 break; 69 } 70 71 BugReport *report = new BugReport(*BT, os.str(), N); 72 report->addRange(SizeE->getSourceRange()); 73 bugreporter::trackNullOrUndefValue(N, SizeE, *report); 74 C.emitReport(report); 75 return; 76 } 77 78 void VLASizeChecker::checkPreStmt(const DeclStmt *DS, CheckerContext &C) const { 79 if (!DS->isSingleDecl()) 80 return; 81 82 const VarDecl *VD = dyn_cast<VarDecl>(DS->getSingleDecl()); 83 if (!VD) 84 return; 85 86 ASTContext &Ctx = C.getASTContext(); 87 const VariableArrayType *VLA = Ctx.getAsVariableArrayType(VD->getType()); 88 if (!VLA) 89 return; 90 91 // FIXME: Handle multi-dimensional VLAs. 92 const Expr *SE = VLA->getSizeExpr(); 93 ProgramStateRef state = C.getState(); 94 SVal sizeV = state->getSVal(SE, C.getLocationContext()); 95 96 if (sizeV.isUndef()) { 97 reportBug(VLA_Garbage, SE, state, C); 98 return; 99 } 100 101 // See if the size value is known. It can't be undefined because we would have 102 // warned about that already. 103 if (sizeV.isUnknown()) 104 return; 105 106 // Check if the size is tainted. 107 if (state->isTainted(sizeV)) { 108 reportBug(VLA_Tainted, SE, 0, C); 109 return; 110 } 111 112 // Check if the size is zero. 113 DefinedSVal sizeD = sizeV.castAs<DefinedSVal>(); 114 115 ProgramStateRef stateNotZero, stateZero; 116 llvm::tie(stateNotZero, stateZero) = state->assume(sizeD); 117 118 if (stateZero && !stateNotZero) { 119 reportBug(VLA_Zero, SE, stateZero, C); 120 return; 121 } 122 123 // From this point on, assume that the size is not zero. 124 state = stateNotZero; 125 126 // VLASizeChecker is responsible for defining the extent of the array being 127 // declared. We do this by multiplying the array length by the element size, 128 // then matching that with the array region's extent symbol. 129 130 // Convert the array length to size_t. 131 SValBuilder &svalBuilder = C.getSValBuilder(); 132 QualType SizeTy = Ctx.getSizeType(); 133 NonLoc ArrayLength = 134 svalBuilder.evalCast(sizeD, SizeTy, SE->getType()).castAs<NonLoc>(); 135 136 // Get the element size. 137 CharUnits EleSize = Ctx.getTypeSizeInChars(VLA->getElementType()); 138 SVal EleSizeVal = svalBuilder.makeIntVal(EleSize.getQuantity(), SizeTy); 139 140 // Multiply the array length by the element size. 141 SVal ArraySizeVal = svalBuilder.evalBinOpNN( 142 state, BO_Mul, ArrayLength, EleSizeVal.castAs<NonLoc>(), SizeTy); 143 144 // Finally, assume that the array's extent matches the given size. 145 const LocationContext *LC = C.getLocationContext(); 146 DefinedOrUnknownSVal Extent = 147 state->getRegion(VD, LC)->getExtent(svalBuilder); 148 DefinedOrUnknownSVal ArraySize = ArraySizeVal.castAs<DefinedOrUnknownSVal>(); 149 DefinedOrUnknownSVal sizeIsKnown = 150 svalBuilder.evalEQ(state, Extent, ArraySize); 151 state = state->assume(sizeIsKnown, true); 152 153 // Assume should not fail at this point. 154 assert(state); 155 156 // Remember our assumptions! 157 C.addTransition(state); 158 } 159 160 void ento::registerVLASizeChecker(CheckerManager &mgr) { 161 mgr.registerChecker<VLASizeChecker>(); 162 } 163
