DivZeroChecker.cpp revision 360660 
1//== DivZeroChecker.cpp - Division by zero checker --------------*- C++ -*--==//
2//
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
6//
7//===----------------------------------------------------------------------===//
8//
9// This defines DivZeroChecker, a builtin check in ExprEngine that performs
10// checks for division by zeros.
11//
12//===----------------------------------------------------------------------===//
13
14#include "Taint.h"
15#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.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
21using namespace clang;
22using namespace ento;
23using namespace taint;
24
25namespace {
26class DivZeroChecker : public Checker< check::PreStmt<BinaryOperator> > {
27  mutable std::unique_ptr<BuiltinBug> BT;
28  void reportBug(const char *Msg, ProgramStateRef StateZero, CheckerContext &C,
29                 std::unique_ptr<BugReporterVisitor> Visitor = nullptr) const;
30
31public:
32  void checkPreStmt(const BinaryOperator *B, CheckerContext &C) const;
33};
34} // end anonymous namespace
35
36static const Expr *getDenomExpr(const ExplodedNode *N) {
37  const Stmt *S = N->getLocationAs<PreStmt>()->getStmt();
38  if (const auto *BE = dyn_cast<BinaryOperator>(S))
39    return BE->getRHS();
40  return nullptr;
41}
42
43void DivZeroChecker::reportBug(
44    const char *Msg, ProgramStateRef StateZero, CheckerContext &C,
45    std::unique_ptr<BugReporterVisitor> Visitor) const {
46  if (ExplodedNode *N = C.generateErrorNode(StateZero)) {
47    if (!BT)
48      BT.reset(new BuiltinBug(this, "Division by zero"));
49
50    auto R = llvm::make_unique<BugReport>(*BT, Msg, N);
51    R->addVisitor(std::move(Visitor));
52    bugreporter::trackExpressionValue(N, getDenomExpr(N), *R);
53    C.emitReport(std::move(R));
54  }
55}
56
57void DivZeroChecker::checkPreStmt(const BinaryOperator *B,
58                                  CheckerContext &C) const {
59  BinaryOperator::Opcode Op = B->getOpcode();
60  if (Op != BO_Div &&
61      Op != BO_Rem &&
62      Op != BO_DivAssign &&
63      Op != BO_RemAssign)
64    return;
65
66  if (!B->getRHS()->getType()->isScalarType())
67    return;
68
69  SVal Denom = C.getSVal(B->getRHS());
70  Optional<DefinedSVal> DV = Denom.getAs<DefinedSVal>();
71
72  // Divide-by-undefined handled in the generic checking for uses of
73  // undefined values.
74  if (!DV)
75    return;
76
77  // Check for divide by zero.
78  ConstraintManager &CM = C.getConstraintManager();
79  ProgramStateRef stateNotZero, stateZero;
80  std::tie(stateNotZero, stateZero) = CM.assumeDual(C.getState(), *DV);
81
82  if (!stateNotZero) {
83    assert(stateZero);
84    reportBug("Division by zero", stateZero, C);
85    return;
86  }
87
88  bool TaintedD = isTainted(C.getState(), *DV);
89  if ((stateNotZero && stateZero && TaintedD)) {
90    reportBug("Division by a tainted value, possibly zero", stateZero, C,
91              llvm::make_unique<taint::TaintBugVisitor>(*DV));
92    return;
93  }
94
95  // If we get here, then the denom should not be zero. We abandon the implicit
96  // zero denom case for now.
97  C.addTransition(stateNotZero);
98}
99
100void ento::registerDivZeroChecker(CheckerManager &mgr) {
101  mgr.registerChecker<DivZeroChecker>();
102}
103
104bool ento::shouldRegisterDivZeroChecker(const LangOptions &LO) {
105  return true;
106}
107