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<BugType> BT;
29   mutable std::unique_ptr<BugType> TaintBT;
30   void reportBug(StringRef Msg, ProgramStateRef StateZero,
31                  CheckerContext &C) const;
32   void reportTaintBug(StringRef Msg, ProgramStateRef StateZero,
33                       CheckerContext &C,
34                       llvm::ArrayRef<SymbolRef> TaintedSyms) const;
35 
36 public:
37   void checkPreStmt(const BinaryOperator *B, CheckerContext &C) const;
38 };
39 } // end anonymous namespace
40 
41 static const Expr *getDenomExpr(const ExplodedNode *N) {
42   const Stmt *S = N->getLocationAs<PreStmt>()->getStmt();
43   if (const auto *BE = dyn_cast<BinaryOperator>(S))
44     return BE->getRHS();
45   return nullptr;
46 }
47 
48 void DivZeroChecker::reportBug(StringRef Msg, ProgramStateRef StateZero,
49                                CheckerContext &C) const {
50   if (ExplodedNode *N = C.generateErrorNode(StateZero)) {
51     if (!BT)
52       BT.reset(new BugType(this, "Division by zero", categories::LogicError));
53 
54     auto R = std::make_unique<PathSensitiveBugReport>(*BT, Msg, N);
55     bugreporter::trackExpressionValue(N, getDenomExpr(N), *R);
56     C.emitReport(std::move(R));
57   }
58 }
59 
60 void DivZeroChecker::reportTaintBug(
61     StringRef Msg, ProgramStateRef StateZero, CheckerContext &C,
62     llvm::ArrayRef<SymbolRef> TaintedSyms) const {
63   if (ExplodedNode *N = C.generateErrorNode(StateZero)) {
64     if (!TaintBT)
65       TaintBT.reset(
66           new BugType(this, "Division by zero", categories::TaintedData));
67 
68     auto R = std::make_unique<PathSensitiveBugReport>(*TaintBT, Msg, N);
69     bugreporter::trackExpressionValue(N, getDenomExpr(N), *R);
70     for (auto Sym : TaintedSyms)
71       R->markInteresting(Sym);
72     C.emitReport(std::move(R));
73   }
74 }
75 
76 void DivZeroChecker::checkPreStmt(const BinaryOperator *B,
77                                   CheckerContext &C) const {
78   BinaryOperator::Opcode Op = B->getOpcode();
79   if (Op != BO_Div &&
80       Op != BO_Rem &&
81       Op != BO_DivAssign &&
82       Op != BO_RemAssign)
83     return;
84 
85   if (!B->getRHS()->getType()->isScalarType())
86     return;
87 
88   SVal Denom = C.getSVal(B->getRHS());
89   std::optional<DefinedSVal> DV = Denom.getAs<DefinedSVal>();
90 
91   // Divide-by-undefined handled in the generic checking for uses of
92   // undefined values.
93   if (!DV)
94     return;
95 
96   // Check for divide by zero.
97   ConstraintManager &CM = C.getConstraintManager();
98   ProgramStateRef stateNotZero, stateZero;
99   std::tie(stateNotZero, stateZero) = CM.assumeDual(C.getState(), *DV);
100 
101   if (!stateNotZero) {
102     assert(stateZero);
103     reportBug("Division by zero", stateZero, C);
104     return;
105   }
106 
107   if ((stateNotZero && stateZero)) {
108     std::vector<SymbolRef> taintedSyms = getTaintedSymbols(C.getState(), *DV);
109     if (!taintedSyms.empty()) {
110       reportTaintBug("Division by a tainted value, possibly zero", stateZero, C,
111                      taintedSyms);
112       return;
113     }
114   }
115 
116   // If we get here, then the denom should not be zero. We abandon the implicit
117   // zero denom case for now.
118   C.addTransition(stateNotZero);
119 }
120 
121 void ento::registerDivZeroChecker(CheckerManager &mgr) {
122   mgr.registerChecker<DivZeroChecker>();
123 }
124 
125 bool ento::shouldRegisterDivZeroChecker(const CheckerManager &mgr) {
126   return true;
127 }
128