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 27using namespace clang; 28using namespace ento; 29 30namespace { 31class VLASizeChecker : public Checker< check::PreStmt<DeclStmt> > { 32 mutable std::unique_ptr<BugType> BT; 33 enum VLASize_Kind { VLA_Garbage, VLA_Zero, VLA_Tainted, VLA_Negative }; 34 35 void reportBug(VLASize_Kind Kind, 36 const Expr *SizeE, 37 ProgramStateRef State, 38 CheckerContext &C) const; 39public: 40 void checkPreStmt(const DeclStmt *DS, CheckerContext &C) const; 41}; 42} // end anonymous namespace 43 44void 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.generateErrorNode(State); 50 if (!N) 51 return; 52 53 if (!BT) 54 BT.reset(new BuiltinBug( 55 this, "Dangerous variable-length array (VLA) declaration")); 56 57 SmallString<256> buf; 58 llvm::raw_svector_ostream os(buf); 59 os << "Declared variable-length array (VLA) "; 60 switch (Kind) { 61 case VLA_Garbage: 62 os << "uses a garbage value as its size"; 63 break; 64 case VLA_Zero: 65 os << "has zero size"; 66 break; 67 case VLA_Tainted: 68 os << "has tainted size"; 69 break; 70 case VLA_Negative: 71 os << "has negative size"; 72 break; 73 } 74 75 auto report = llvm::make_unique<BugReport>(*BT, os.str(), N); 76 report->addRange(SizeE->getSourceRange()); 77 bugreporter::trackNullOrUndefValue(N, SizeE, *report); 78 C.emitReport(std::move(report)); 79} 80 81void VLASizeChecker::checkPreStmt(const DeclStmt *DS, CheckerContext &C) const { 82 if (!DS->isSingleDecl()) 83 return; 84 85 const VarDecl *VD = dyn_cast<VarDecl>(DS->getSingleDecl()); 86 if (!VD) 87 return; 88 89 ASTContext &Ctx = C.getASTContext(); 90 const VariableArrayType *VLA = Ctx.getAsVariableArrayType(VD->getType()); 91 if (!VLA) 92 return; 93 94 // FIXME: Handle multi-dimensional VLAs. 95 const Expr *SE = VLA->getSizeExpr(); 96 ProgramStateRef state = C.getState(); 97 SVal sizeV = state->getSVal(SE, C.getLocationContext()); 98 99 if (sizeV.isUndef()) { 100 reportBug(VLA_Garbage, SE, state, C); 101 return; 102 } 103 104 // See if the size value is known. It can't be undefined because we would have 105 // warned about that already. 106 if (sizeV.isUnknown()) 107 return; 108 109 // Check if the size is tainted. 110 if (state->isTainted(sizeV)) { 111 reportBug(VLA_Tainted, SE, nullptr, C); 112 return; 113 } 114 115 // Check if the size is zero. 116 DefinedSVal sizeD = sizeV.castAs<DefinedSVal>(); 117 118 ProgramStateRef stateNotZero, stateZero; 119 std::tie(stateNotZero, stateZero) = state->assume(sizeD); 120 121 if (stateZero && !stateNotZero) { 122 reportBug(VLA_Zero, SE, stateZero, C); 123 return; 124 } 125 126 // From this point on, assume that the size is not zero. 127 state = stateNotZero; 128 129 // VLASizeChecker is responsible for defining the extent of the array being 130 // declared. We do this by multiplying the array length by the element size, 131 // then matching that with the array region's extent symbol. 132 133 // Check if the size is negative. 134 SValBuilder &svalBuilder = C.getSValBuilder(); 135 136 QualType Ty = SE->getType(); 137 DefinedOrUnknownSVal Zero = svalBuilder.makeZeroVal(Ty); 138 139 SVal LessThanZeroVal = svalBuilder.evalBinOp(state, BO_LT, sizeD, Zero, Ty); 140 if (Optional<DefinedSVal> LessThanZeroDVal = 141 LessThanZeroVal.getAs<DefinedSVal>()) { 142 ConstraintManager &CM = C.getConstraintManager(); 143 ProgramStateRef StatePos, StateNeg; 144 145 std::tie(StateNeg, StatePos) = CM.assumeDual(state, *LessThanZeroDVal); 146 if (StateNeg && !StatePos) { 147 reportBug(VLA_Negative, SE, state, C); 148 return; 149 } 150 state = StatePos; 151 } 152 153 // Convert the array length to size_t. 154 QualType SizeTy = Ctx.getSizeType(); 155 NonLoc ArrayLength = 156 svalBuilder.evalCast(sizeD, SizeTy, SE->getType()).castAs<NonLoc>(); 157 158 // Get the element size. 159 CharUnits EleSize = Ctx.getTypeSizeInChars(VLA->getElementType()); 160 SVal EleSizeVal = svalBuilder.makeIntVal(EleSize.getQuantity(), SizeTy); 161 162 // Multiply the array length by the element size. 163 SVal ArraySizeVal = svalBuilder.evalBinOpNN( 164 state, BO_Mul, ArrayLength, EleSizeVal.castAs<NonLoc>(), SizeTy); 165 166 // Finally, assume that the array's extent matches the given size. 167 const LocationContext *LC = C.getLocationContext(); 168 DefinedOrUnknownSVal Extent = 169 state->getRegion(VD, LC)->getExtent(svalBuilder); 170 DefinedOrUnknownSVal ArraySize = ArraySizeVal.castAs<DefinedOrUnknownSVal>(); 171 DefinedOrUnknownSVal sizeIsKnown = 172 svalBuilder.evalEQ(state, Extent, ArraySize); 173 state = state->assume(sizeIsKnown, true); 174 175 // Assume should not fail at this point. 176 assert(state); 177 178 // Remember our assumptions! 179 C.addTransition(state); 180} 181 182void ento::registerVLASizeChecker(CheckerManager &mgr) { 183 mgr.registerChecker<VLASizeChecker>(); 184} 185