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/Core/BugReporter/BugType.h"
16 #include "clang/StaticAnalyzer/Core/Checker.h"
17 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
18 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
19 
20 using namespace clang;
21 using namespace ento;
22 
23 namespace {
24 class DivZeroChecker : public Checker< check::PreStmt<BinaryOperator> > {
25   mutable std::unique_ptr<BuiltinBug> BT;
26   void reportBug(const char *Msg, ProgramStateRef StateZero, CheckerContext &C,
27                  std::unique_ptr<BugReporterVisitor> Visitor = nullptr) const;
28 
29 public:
30   void checkPreStmt(const BinaryOperator *B, CheckerContext &C) const;
31 };
32 } // end anonymous namespace
33 
34 static const Expr *getDenomExpr(const ExplodedNode *N) {
35   const Stmt *S = N->getLocationAs<PreStmt>()->getStmt();
36   if (const auto *BE = dyn_cast<BinaryOperator>(S))
37     return BE->getRHS();
38   return nullptr;
39 }
40 
41 void DivZeroChecker::reportBug(
42     const char *Msg, ProgramStateRef StateZero, CheckerContext &C,
43     std::unique_ptr<BugReporterVisitor> Visitor) const {
44   if (ExplodedNode *N = C.generateErrorNode(StateZero)) {
45     if (!BT)
46       BT.reset(new BuiltinBug(this, "Division by zero"));
47 
48     auto R = llvm::make_unique<BugReport>(*BT, Msg, N);
49     R->addVisitor(std::move(Visitor));
50     bugreporter::trackExpressionValue(N, getDenomExpr(N), *R);
51     C.emitReport(std::move(R));
52   }
53 }
54 
55 void DivZeroChecker::checkPreStmt(const BinaryOperator *B,
56                                   CheckerContext &C) const {
57   BinaryOperator::Opcode Op = B->getOpcode();
58   if (Op != BO_Div &&
59       Op != BO_Rem &&
60       Op != BO_DivAssign &&
61       Op != BO_RemAssign)
62     return;
63 
64   if (!B->getRHS()->getType()->isScalarType())
65     return;
66 
67   SVal Denom = C.getSVal(B->getRHS());
68   Optional<DefinedSVal> DV = Denom.getAs<DefinedSVal>();
69 
70   // Divide-by-undefined handled in the generic checking for uses of
71   // undefined values.
72   if (!DV)
73     return;
74 
75   // Check for divide by zero.
76   ConstraintManager &CM = C.getConstraintManager();
77   ProgramStateRef stateNotZero, stateZero;
78   std::tie(stateNotZero, stateZero) = CM.assumeDual(C.getState(), *DV);
79 
80   if (!stateNotZero) {
81     assert(stateZero);
82     reportBug("Division by zero", stateZero, C);
83     return;
84   }
85 
86   bool TaintedD = C.getState()->isTainted(*DV);
87   if ((stateNotZero && stateZero && TaintedD)) {
88     reportBug("Division by a tainted value, possibly zero", stateZero, C,
89               llvm::make_unique<TaintBugVisitor>(*DV));
90     return;
91   }
92 
93   // If we get here, then the denom should not be zero. We abandon the implicit
94   // zero denom case for now.
95   C.addTransition(stateNotZero);
96 }
97 
98 void ento::registerDivZeroChecker(CheckerManager &mgr) {
99   mgr.registerChecker<DivZeroChecker>();
100 }
101 
102 bool ento::shouldRegisterDivZeroChecker(const LangOptions &LO) {
103   return true;
104 }
105