1 //=== VLASizeChecker.cpp - Undefined dereference checker --------*- C++ -*-===//
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //===----------------------------------------------------------------------===//
9 // This defines VLASizeChecker, a builtin check in ExprEngine that
10 // performs checks for declaration of VLA of undefined or zero size.
11 // In addition, VLASizeChecker is responsible for defining the extent
12 // of the MemRegion that represents a VLA.
14 //===----------------------------------------------------------------------===//
17 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.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"
27 using namespace clang;
29 using namespace taint;
32 class VLASizeChecker : public Checker< check::PreStmt<DeclStmt> > {
33 mutable std::unique_ptr<BugType> BT;
34 enum VLASize_Kind { VLA_Garbage, VLA_Zero, VLA_Tainted, VLA_Negative };
36 void reportBug(VLASize_Kind Kind, const Expr *SizeE, ProgramStateRef State,
38 std::unique_ptr<BugReporterVisitor> Visitor = nullptr) const;
41 void checkPreStmt(const DeclStmt *DS, CheckerContext &C) const;
43 } // end anonymous namespace
45 void VLASizeChecker::reportBug(
46 VLASize_Kind Kind, const Expr *SizeE, ProgramStateRef State,
47 CheckerContext &C, std::unique_ptr<BugReporterVisitor> Visitor) const {
48 // Generate an error node.
49 ExplodedNode *N = C.generateErrorNode(State);
54 BT.reset(new BuiltinBug(
55 this, "Dangerous variable-length array (VLA) declaration"));
58 llvm::raw_svector_ostream os(buf);
59 os << "Declared variable-length array (VLA) ";
62 os << "uses a garbage value as its size";
65 os << "has zero size";
68 os << "has tainted size";
71 os << "has negative size";
75 auto report = std::make_unique<PathSensitiveBugReport>(*BT, os.str(), N);
76 report->addVisitor(std::move(Visitor));
77 report->addRange(SizeE->getSourceRange());
78 bugreporter::trackExpressionValue(N, SizeE, *report);
79 C.emitReport(std::move(report));
82 void VLASizeChecker::checkPreStmt(const DeclStmt *DS, CheckerContext &C) const {
83 if (!DS->isSingleDecl())
86 const VarDecl *VD = dyn_cast<VarDecl>(DS->getSingleDecl());
90 ASTContext &Ctx = C.getASTContext();
91 const VariableArrayType *VLA = Ctx.getAsVariableArrayType(VD->getType());
95 // FIXME: Handle multi-dimensional VLAs.
96 const Expr *SE = VLA->getSizeExpr();
97 ProgramStateRef state = C.getState();
98 SVal sizeV = C.getSVal(SE);
100 if (sizeV.isUndef()) {
101 reportBug(VLA_Garbage, SE, state, C);
105 // See if the size value is known. It can't be undefined because we would have
106 // warned about that already.
107 if (sizeV.isUnknown())
110 // Check if the size is tainted.
111 if (isTainted(state, sizeV)) {
112 reportBug(VLA_Tainted, SE, nullptr, C,
113 std::make_unique<TaintBugVisitor>(sizeV));
117 // Check if the size is zero.
118 DefinedSVal sizeD = sizeV.castAs<DefinedSVal>();
120 ProgramStateRef stateNotZero, stateZero;
121 std::tie(stateNotZero, stateZero) = state->assume(sizeD);
123 if (stateZero && !stateNotZero) {
124 reportBug(VLA_Zero, SE, stateZero, C);
128 // From this point on, assume that the size is not zero.
129 state = stateNotZero;
131 // VLASizeChecker is responsible for defining the extent of the array being
132 // declared. We do this by multiplying the array length by the element size,
133 // then matching that with the array region's extent symbol.
135 // Check if the size is negative.
136 SValBuilder &svalBuilder = C.getSValBuilder();
138 QualType Ty = SE->getType();
139 DefinedOrUnknownSVal Zero = svalBuilder.makeZeroVal(Ty);
141 SVal LessThanZeroVal = svalBuilder.evalBinOp(state, BO_LT, sizeD, Zero, Ty);
142 if (Optional<DefinedSVal> LessThanZeroDVal =
143 LessThanZeroVal.getAs<DefinedSVal>()) {
144 ConstraintManager &CM = C.getConstraintManager();
145 ProgramStateRef StatePos, StateNeg;
147 std::tie(StateNeg, StatePos) = CM.assumeDual(state, *LessThanZeroDVal);
148 if (StateNeg && !StatePos) {
149 reportBug(VLA_Negative, SE, state, C);
155 // Convert the array length to size_t.
156 QualType SizeTy = Ctx.getSizeType();
158 svalBuilder.evalCast(sizeD, SizeTy, SE->getType()).castAs<NonLoc>();
160 // Get the element size.
161 CharUnits EleSize = Ctx.getTypeSizeInChars(VLA->getElementType());
162 SVal EleSizeVal = svalBuilder.makeIntVal(EleSize.getQuantity(), SizeTy);
164 // Multiply the array length by the element size.
165 SVal ArraySizeVal = svalBuilder.evalBinOpNN(
166 state, BO_Mul, ArrayLength, EleSizeVal.castAs<NonLoc>(), SizeTy);
168 // Finally, assume that the array's extent matches the given size.
169 const LocationContext *LC = C.getLocationContext();
170 DefinedOrUnknownSVal Extent =
171 state->getRegion(VD, LC)->getExtent(svalBuilder);
172 DefinedOrUnknownSVal ArraySize = ArraySizeVal.castAs<DefinedOrUnknownSVal>();
173 DefinedOrUnknownSVal sizeIsKnown =
174 svalBuilder.evalEQ(state, Extent, ArraySize);
175 state = state->assume(sizeIsKnown, true);
177 // Assume should not fail at this point.
180 // Remember our assumptions!
181 C.addTransition(state);
184 void ento::registerVLASizeChecker(CheckerManager &mgr) {
185 mgr.registerChecker<VLASizeChecker>();
188 bool ento::shouldRegisterVLASizeChecker(const LangOptions &LO) {