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 "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
15 #include "clang/StaticAnalyzer/Checkers/Taint.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 #include <optional>
21 
22 using namespace clang;
23 using namespace ento;
24 using namespace taint;
25 
26 namespace {
27 class DivZeroChecker : public Checker< check::PreStmt<BinaryOperator> > {
28   mutable std::unique_ptr<BuiltinBug> BT;
29   void reportBug(const char *Msg, ProgramStateRef StateZero, CheckerContext &C,
30                  std::unique_ptr<BugReporterVisitor> Visitor = nullptr) const;
31 
32 public:
33   void checkPreStmt(const BinaryOperator *B, CheckerContext &C) const;
34 };
35 } // end anonymous namespace
36 
37 static const Expr *getDenomExpr(const ExplodedNode *N) {
38   const Stmt *S = N->getLocationAs<PreStmt>()->getStmt();
39   if (const auto *BE = dyn_cast<BinaryOperator>(S))
40     return BE->getRHS();
41   return nullptr;
42 }
43 
44 void DivZeroChecker::reportBug(
45     const char *Msg, ProgramStateRef StateZero, CheckerContext &C,
46     std::unique_ptr<BugReporterVisitor> Visitor) const {
47   if (ExplodedNode *N = C.generateErrorNode(StateZero)) {
48     if (!BT)
49       BT.reset(new BuiltinBug(this, "Division by zero"));
50 
51     auto R = std::make_unique<PathSensitiveBugReport>(*BT, Msg, N);
52     R->addVisitor(std::move(Visitor));
53     bugreporter::trackExpressionValue(N, getDenomExpr(N), *R);
54     C.emitReport(std::move(R));
55   }
56 }
57 
58 void DivZeroChecker::checkPreStmt(const BinaryOperator *B,
59                                   CheckerContext &C) const {
60   BinaryOperator::Opcode Op = B->getOpcode();
61   if (Op != BO_Div &&
62       Op != BO_Rem &&
63       Op != BO_DivAssign &&
64       Op != BO_RemAssign)
65     return;
66 
67   if (!B->getRHS()->getType()->isScalarType())
68     return;
69 
70   SVal Denom = C.getSVal(B->getRHS());
71   std::optional<DefinedSVal> DV = Denom.getAs<DefinedSVal>();
72 
73   // Divide-by-undefined handled in the generic checking for uses of
74   // undefined values.
75   if (!DV)
76     return;
77 
78   // Check for divide by zero.
79   ConstraintManager &CM = C.getConstraintManager();
80   ProgramStateRef stateNotZero, stateZero;
81   std::tie(stateNotZero, stateZero) = CM.assumeDual(C.getState(), *DV);
82 
83   if (!stateNotZero) {
84     assert(stateZero);
85     reportBug("Division by zero", stateZero, C);
86     return;
87   }
88 
89   bool TaintedD = isTainted(C.getState(), *DV);
90   if ((stateNotZero && stateZero && TaintedD)) {
91     reportBug("Division by a tainted value, possibly zero", stateZero, C,
92               std::make_unique<taint::TaintBugVisitor>(*DV));
93     return;
94   }
95 
96   // If we get here, then the denom should not be zero. We abandon the implicit
97   // zero denom case for now.
98   C.addTransition(stateNotZero);
99 }
100 
101 void ento::registerDivZeroChecker(CheckerManager &mgr) {
102   mgr.registerChecker<DivZeroChecker>();
103 }
104 
105 bool ento::shouldRegisterDivZeroChecker(const CheckerManager &mgr) {
106   return true;
107 }
108