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1 //== DivZeroChecker.cpp - Division by zero checker --------------*- C++ -*--==//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This defines DivZeroChecker, a builtin check in ExprEngine that performs
11 // checks for division by zeros.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #include "ClangSACheckers.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 
24 namespace {
25 class DivZeroChecker : public Checker< check::PreStmt<BinaryOperator> > {
26   mutable std::unique_ptr<BuiltinBug> BT;
27   void reportBug(const char *Msg,
28                  ProgramStateRef StateZero,
29                  CheckerContext &C) const ;
30 public:
31   void checkPreStmt(const BinaryOperator *B, CheckerContext &C) const;
32 };
33 } // end anonymous namespace
34 
reportBug(const char * Msg,ProgramStateRef StateZero,CheckerContext & C) const35 void DivZeroChecker::reportBug(const char *Msg,
36                                ProgramStateRef StateZero,
37                                CheckerContext &C) const {
38   if (ExplodedNode *N = C.generateErrorNode(StateZero)) {
39     if (!BT)
40       BT.reset(new BuiltinBug(this, "Division by zero"));
41 
42     auto R = llvm::make_unique<BugReport>(*BT, Msg, N);
43     bugreporter::trackNullOrUndefValue(N, bugreporter::GetDenomExpr(N), *R);
44     C.emitReport(std::move(R));
45   }
46 }
47 
checkPreStmt(const BinaryOperator * B,CheckerContext & C) const48 void DivZeroChecker::checkPreStmt(const BinaryOperator *B,
49                                   CheckerContext &C) const {
50   BinaryOperator::Opcode Op = B->getOpcode();
51   if (Op != BO_Div &&
52       Op != BO_Rem &&
53       Op != BO_DivAssign &&
54       Op != BO_RemAssign)
55     return;
56 
57   if (!B->getRHS()->getType()->isScalarType())
58     return;
59 
60   SVal Denom = C.getState()->getSVal(B->getRHS(), C.getLocationContext());
61   Optional<DefinedSVal> DV = Denom.getAs<DefinedSVal>();
62 
63   // Divide-by-undefined handled in the generic checking for uses of
64   // undefined values.
65   if (!DV)
66     return;
67 
68   // Check for divide by zero.
69   ConstraintManager &CM = C.getConstraintManager();
70   ProgramStateRef stateNotZero, stateZero;
71   std::tie(stateNotZero, stateZero) = CM.assumeDual(C.getState(), *DV);
72 
73   if (!stateNotZero) {
74     assert(stateZero);
75     reportBug("Division by zero", stateZero, C);
76     return;
77   }
78 
79   bool TaintedD = C.getState()->isTainted(*DV);
80   if ((stateNotZero && stateZero && TaintedD)) {
81     reportBug("Division by a tainted value, possibly zero", stateZero, C);
82     return;
83   }
84 
85   // If we get here, then the denom should not be zero. We abandon the implicit
86   // zero denom case for now.
87   C.addTransition(stateNotZero);
88 }
89 
registerDivZeroChecker(CheckerManager & mgr)90 void ento::registerDivZeroChecker(CheckerManager &mgr) {
91   mgr.registerChecker<DivZeroChecker>();
92 }
93