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
21 using namespace clang;
22 using namespace ento;
23 using namespace taint;
24
25 namespace {
26 class 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
31 public:
32 void checkPreStmt(const BinaryOperator *B, CheckerContext &C) const;
33 };
34 } // end anonymous namespace
35
getDenomExpr(const ExplodedNode * N)36 static 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
reportBug(const char * Msg,ProgramStateRef StateZero,CheckerContext & C,std::unique_ptr<BugReporterVisitor> Visitor) const43 void 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 = std::make_unique<PathSensitiveBugReport>(*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
checkPreStmt(const BinaryOperator * B,CheckerContext & C) const57 void 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 std::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
registerDivZeroChecker(CheckerManager & mgr)100 void ento::registerDivZeroChecker(CheckerManager &mgr) {
101 mgr.registerChecker<DivZeroChecker>();
102 }
103
shouldRegisterDivZeroChecker(const CheckerManager & mgr)104 bool ento::shouldRegisterDivZeroChecker(const CheckerManager &mgr) {
105 return true;
106 }
107