341 lines
11 KiB
C++
341 lines
11 KiB
C++
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//=== VLASizeChecker.cpp - Undefined dereference checker --------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This defines VLASizeChecker, a builtin check in ExprEngine that
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// performs checks for declaration of VLA of undefined or zero size.
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// In addition, VLASizeChecker is responsible for defining the extent
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// of the MemRegion that represents a VLA.
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//
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//===----------------------------------------------------------------------===//
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#include "Taint.h"
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#include "clang/AST/CharUnits.h"
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#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
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#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
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#include "clang/StaticAnalyzer/Core/Checker.h"
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#include "clang/StaticAnalyzer/Core/CheckerManager.h"
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#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
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#include "clang/StaticAnalyzer/Core/PathSensitive/DynamicSize.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/ADT/SmallString.h"
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#include "llvm/Support/raw_ostream.h"
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using namespace clang;
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using namespace ento;
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using namespace taint;
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namespace {
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class VLASizeChecker
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: public Checker<check::PreStmt<DeclStmt>,
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check::PreStmt<UnaryExprOrTypeTraitExpr>> {
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mutable std::unique_ptr<BugType> BT;
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enum VLASize_Kind {
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VLA_Garbage,
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VLA_Zero,
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VLA_Tainted,
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VLA_Negative,
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VLA_Overflow
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};
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/// Check a VLA for validity.
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/// Every dimension of the array and the total size is checked for validity.
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/// Returns null or a new state where the size is validated.
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/// 'ArraySize' will contain SVal that refers to the total size (in char)
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/// of the array.
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ProgramStateRef checkVLA(CheckerContext &C, ProgramStateRef State,
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const VariableArrayType *VLA, SVal &ArraySize) const;
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/// Check a single VLA index size expression for validity.
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ProgramStateRef checkVLAIndexSize(CheckerContext &C, ProgramStateRef State,
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const Expr *SizeE) const;
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void reportBug(VLASize_Kind Kind, const Expr *SizeE, ProgramStateRef State,
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CheckerContext &C,
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std::unique_ptr<BugReporterVisitor> Visitor = nullptr) const;
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public:
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void checkPreStmt(const DeclStmt *DS, CheckerContext &C) const;
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void checkPreStmt(const UnaryExprOrTypeTraitExpr *UETTE,
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CheckerContext &C) const;
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};
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} // end anonymous namespace
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ProgramStateRef VLASizeChecker::checkVLA(CheckerContext &C,
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ProgramStateRef State,
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const VariableArrayType *VLA,
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SVal &ArraySize) const {
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assert(VLA && "Function should be called with non-null VLA argument.");
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const VariableArrayType *VLALast = nullptr;
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llvm::SmallVector<const Expr *, 2> VLASizes;
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// Walk over the VLAs for every dimension until a non-VLA is found.
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// There is a VariableArrayType for every dimension (fixed or variable) until
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// the most inner array that is variably modified.
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// Dimension sizes are collected into 'VLASizes'. 'VLALast' is set to the
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// innermost VLA that was encountered.
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// In "int vla[x][2][y][3]" this will be the array for index "y" (with type
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// int[3]). 'VLASizes' contains 'x', '2', and 'y'.
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while (VLA) {
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const Expr *SizeE = VLA->getSizeExpr();
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State = checkVLAIndexSize(C, State, SizeE);
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if (!State)
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return nullptr;
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VLASizes.push_back(SizeE);
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VLALast = VLA;
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VLA = C.getASTContext().getAsVariableArrayType(VLA->getElementType());
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};
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assert(VLALast &&
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"Array should have at least one variably-modified dimension.");
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ASTContext &Ctx = C.getASTContext();
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SValBuilder &SVB = C.getSValBuilder();
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CanQualType SizeTy = Ctx.getSizeType();
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uint64_t SizeMax =
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SVB.getBasicValueFactory().getMaxValue(SizeTy).getZExtValue();
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// Get the element size.
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CharUnits EleSize = Ctx.getTypeSizeInChars(VLALast->getElementType());
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NonLoc ArrSize =
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SVB.makeIntVal(EleSize.getQuantity(), SizeTy).castAs<NonLoc>();
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// Try to calculate the known real size of the array in KnownSize.
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uint64_t KnownSize = 0;
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if (const llvm::APSInt *KV = SVB.getKnownValue(State, ArrSize))
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KnownSize = KV->getZExtValue();
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for (const Expr *SizeE : VLASizes) {
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auto SizeD = C.getSVal(SizeE).castAs<DefinedSVal>();
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// Convert the array length to size_t.
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NonLoc IndexLength =
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SVB.evalCast(SizeD, SizeTy, SizeE->getType()).castAs<NonLoc>();
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// Multiply the array length by the element size.
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SVal Mul = SVB.evalBinOpNN(State, BO_Mul, ArrSize, IndexLength, SizeTy);
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if (auto MulNonLoc = Mul.getAs<NonLoc>())
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ArrSize = *MulNonLoc;
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else
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// Extent could not be determined.
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return State;
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if (const llvm::APSInt *IndexLVal = SVB.getKnownValue(State, IndexLength)) {
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// Check if the array size will overflow.
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// Size overflow check does not work with symbolic expressions because a
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// overflow situation can not be detected easily.
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uint64_t IndexL = IndexLVal->getZExtValue();
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// FIXME: See https://reviews.llvm.org/D80903 for discussion of
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// some difference in assume and getKnownValue that leads to
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// unexpected behavior. Just bail on IndexL == 0 at this point.
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if (IndexL == 0)
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return nullptr;
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if (KnownSize <= SizeMax / IndexL) {
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KnownSize *= IndexL;
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} else {
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// Array size does not fit into size_t.
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reportBug(VLA_Overflow, SizeE, State, C);
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return nullptr;
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}
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} else {
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KnownSize = 0;
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}
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}
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ArraySize = ArrSize;
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return State;
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}
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ProgramStateRef VLASizeChecker::checkVLAIndexSize(CheckerContext &C,
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ProgramStateRef State,
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const Expr *SizeE) const {
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SVal SizeV = C.getSVal(SizeE);
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if (SizeV.isUndef()) {
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reportBug(VLA_Garbage, SizeE, State, C);
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return nullptr;
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}
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// See if the size value is known. It can't be undefined because we would have
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// warned about that already.
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if (SizeV.isUnknown())
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return nullptr;
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// Check if the size is tainted.
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if (isTainted(State, SizeV)) {
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reportBug(VLA_Tainted, SizeE, nullptr, C,
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std::make_unique<TaintBugVisitor>(SizeV));
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return nullptr;
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}
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// Check if the size is zero.
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DefinedSVal SizeD = SizeV.castAs<DefinedSVal>();
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ProgramStateRef StateNotZero, StateZero;
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std::tie(StateNotZero, StateZero) = State->assume(SizeD);
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if (StateZero && !StateNotZero) {
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reportBug(VLA_Zero, SizeE, StateZero, C);
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return nullptr;
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}
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// From this point on, assume that the size is not zero.
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State = StateNotZero;
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// Check if the size is negative.
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SValBuilder &SVB = C.getSValBuilder();
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QualType SizeTy = SizeE->getType();
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DefinedOrUnknownSVal Zero = SVB.makeZeroVal(SizeTy);
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SVal LessThanZeroVal = SVB.evalBinOp(State, BO_LT, SizeD, Zero, SizeTy);
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if (Optional<DefinedSVal> LessThanZeroDVal =
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LessThanZeroVal.getAs<DefinedSVal>()) {
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ConstraintManager &CM = C.getConstraintManager();
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ProgramStateRef StatePos, StateNeg;
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std::tie(StateNeg, StatePos) = CM.assumeDual(State, *LessThanZeroDVal);
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if (StateNeg && !StatePos) {
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reportBug(VLA_Negative, SizeE, State, C);
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return nullptr;
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}
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State = StatePos;
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}
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return State;
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}
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void VLASizeChecker::reportBug(
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VLASize_Kind Kind, const Expr *SizeE, ProgramStateRef State,
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CheckerContext &C, std::unique_ptr<BugReporterVisitor> Visitor) const {
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// Generate an error node.
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ExplodedNode *N = C.generateErrorNode(State);
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if (!N)
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return;
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if (!BT)
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BT.reset(new BuiltinBug(
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this, "Dangerous variable-length array (VLA) declaration"));
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SmallString<256> buf;
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llvm::raw_svector_ostream os(buf);
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os << "Declared variable-length array (VLA) ";
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switch (Kind) {
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case VLA_Garbage:
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os << "uses a garbage value as its size";
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break;
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case VLA_Zero:
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os << "has zero size";
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break;
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case VLA_Tainted:
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os << "has tainted size";
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break;
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case VLA_Negative:
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os << "has negative size";
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break;
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case VLA_Overflow:
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os << "has too large size";
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break;
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}
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auto report = std::make_unique<PathSensitiveBugReport>(*BT, os.str(), N);
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report->addVisitor(std::move(Visitor));
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report->addRange(SizeE->getSourceRange());
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bugreporter::trackExpressionValue(N, SizeE, *report);
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C.emitReport(std::move(report));
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}
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void VLASizeChecker::checkPreStmt(const DeclStmt *DS, CheckerContext &C) const {
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if (!DS->isSingleDecl())
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return;
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ASTContext &Ctx = C.getASTContext();
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SValBuilder &SVB = C.getSValBuilder();
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ProgramStateRef State = C.getState();
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QualType TypeToCheck;
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const VarDecl *VD = dyn_cast<VarDecl>(DS->getSingleDecl());
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if (VD)
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TypeToCheck = VD->getType().getCanonicalType();
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else if (const auto *TND = dyn_cast<TypedefNameDecl>(DS->getSingleDecl()))
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TypeToCheck = TND->getUnderlyingType().getCanonicalType();
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else
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return;
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const VariableArrayType *VLA = Ctx.getAsVariableArrayType(TypeToCheck);
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if (!VLA)
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return;
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// Check the VLA sizes for validity.
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SVal ArraySize;
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State = checkVLA(C, State, VLA, ArraySize);
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if (!State)
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return;
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auto ArraySizeNL = ArraySize.getAs<NonLoc>();
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if (!ArraySizeNL) {
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// Array size could not be determined but state may contain new assumptions.
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C.addTransition(State);
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return;
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}
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// VLASizeChecker is responsible for defining the extent of the array being
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// declared. We do this by multiplying the array length by the element size,
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// then matching that with the array region's extent symbol.
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if (VD) {
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// Assume that the array's size matches the region size.
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const LocationContext *LC = C.getLocationContext();
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DefinedOrUnknownSVal DynSize =
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getDynamicSize(State, State->getRegion(VD, LC), SVB);
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DefinedOrUnknownSVal SizeIsKnown = SVB.evalEQ(State, DynSize, *ArraySizeNL);
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State = State->assume(SizeIsKnown, true);
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// Assume should not fail at this point.
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assert(State);
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}
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// Remember our assumptions!
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C.addTransition(State);
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}
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void VLASizeChecker::checkPreStmt(const UnaryExprOrTypeTraitExpr *UETTE,
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CheckerContext &C) const {
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// Want to check for sizeof.
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if (UETTE->getKind() != UETT_SizeOf)
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return;
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// Ensure a type argument.
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if (!UETTE->isArgumentType())
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return;
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const VariableArrayType *VLA = C.getASTContext().getAsVariableArrayType(
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UETTE->getTypeOfArgument().getCanonicalType());
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// Ensure that the type is a VLA.
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if (!VLA)
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return;
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ProgramStateRef State = C.getState();
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SVal ArraySize;
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State = checkVLA(C, State, VLA, ArraySize);
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if (!State)
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return;
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C.addTransition(State);
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}
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void ento::registerVLASizeChecker(CheckerManager &mgr) {
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mgr.registerChecker<VLASizeChecker>();
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}
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bool ento::shouldRegisterVLASizeChecker(const CheckerManager &mgr) {
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return true;
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}
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