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
getDenomExpr(const ExplodedNode * N)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
reportBug(const char * Msg,ProgramStateRef StateZero,CheckerContext & C,std::unique_ptr<BugReporterVisitor> Visitor) const44 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
checkPreStmt(const BinaryOperator * B,CheckerContext & C) const58 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
registerDivZeroChecker(CheckerManager & mgr)101 void ento::registerDivZeroChecker(CheckerManager &mgr) {
102 mgr.registerChecker<DivZeroChecker>();
103 }
104
shouldRegisterDivZeroChecker(const CheckerManager & mgr)105 bool ento::shouldRegisterDivZeroChecker(const CheckerManager &mgr) {
106 return true;
107 }
108