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.generateSink(StateZero)) {
39 if (!BT)
40 BT.reset(new BuiltinBug(this, "Division by zero"));
41
42 BugReport *R = new BugReport(*BT, Msg, N);
43 bugreporter::trackNullOrUndefValue(N, bugreporter::GetDenomExpr(N), *R);
44 C.emitReport(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