1 //== ReturnUndefChecker.cpp -------------------------------------*- 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 file defines ReturnUndefChecker, which is a path-sensitive
11 // check which looks for undefined or garbage values being returned to the
12 // caller.
13 //
14 //===----------------------------------------------------------------------===//
15
16 #include "ClangSACheckers.h"
17 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
18 #include "clang/StaticAnalyzer/Core/Checker.h"
19 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
20 #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
21 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
22
23 using namespace clang;
24 using namespace ento;
25
26 namespace {
27 class ReturnUndefChecker : public Checker< check::PreStmt<ReturnStmt> > {
28 mutable OwningPtr<BuiltinBug> BT_Undef;
29 mutable OwningPtr<BuiltinBug> BT_NullReference;
30
31 void emitUndef(CheckerContext &C, const Expr *RetE) const;
32 void checkReference(CheckerContext &C, const Expr *RetE,
33 DefinedOrUnknownSVal RetVal) const;
34 public:
35 void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const;
36 };
37 }
38
checkPreStmt(const ReturnStmt * RS,CheckerContext & C) const39 void ReturnUndefChecker::checkPreStmt(const ReturnStmt *RS,
40 CheckerContext &C) const {
41 const Expr *RetE = RS->getRetValue();
42 if (!RetE)
43 return;
44 SVal RetVal = C.getSVal(RetE);
45
46 const StackFrameContext *SFC = C.getStackFrame();
47 QualType RT = CallEvent::getDeclaredResultType(SFC->getDecl());
48
49 if (RetVal.isUndef()) {
50 // "return;" is modeled to evaluate to an UndefinedVal. Allow UndefinedVal
51 // to be returned in functions returning void to support this pattern:
52 // void foo() {
53 // return;
54 // }
55 // void test() {
56 // return foo();
57 // }
58 if (RT.isNull() || !RT->isVoidType())
59 emitUndef(C, RetE);
60 return;
61 }
62
63 if (RT.isNull())
64 return;
65
66 if (RT->isReferenceType()) {
67 checkReference(C, RetE, RetVal.castAs<DefinedOrUnknownSVal>());
68 return;
69 }
70 }
71
emitBug(CheckerContext & C,BuiltinBug & BT,const Expr * RetE,const Expr * TrackingE=0)72 static void emitBug(CheckerContext &C, BuiltinBug &BT, const Expr *RetE,
73 const Expr *TrackingE = 0) {
74 ExplodedNode *N = C.generateSink();
75 if (!N)
76 return;
77
78 BugReport *Report = new BugReport(BT, BT.getDescription(), N);
79
80 Report->addRange(RetE->getSourceRange());
81 bugreporter::trackNullOrUndefValue(N, TrackingE ? TrackingE : RetE, *Report);
82
83 C.emitReport(Report);
84 }
85
emitUndef(CheckerContext & C,const Expr * RetE) const86 void ReturnUndefChecker::emitUndef(CheckerContext &C, const Expr *RetE) const {
87 if (!BT_Undef)
88 BT_Undef.reset(new BuiltinBug("Garbage return value",
89 "Undefined or garbage value "
90 "returned to caller"));
91 emitBug(C, *BT_Undef, RetE);
92 }
93
checkReference(CheckerContext & C,const Expr * RetE,DefinedOrUnknownSVal RetVal) const94 void ReturnUndefChecker::checkReference(CheckerContext &C, const Expr *RetE,
95 DefinedOrUnknownSVal RetVal) const {
96 ProgramStateRef StNonNull, StNull;
97 llvm::tie(StNonNull, StNull) = C.getState()->assume(RetVal);
98
99 if (StNonNull) {
100 // Going forward, assume the location is non-null.
101 C.addTransition(StNonNull);
102 return;
103 }
104
105 // The return value is known to be null. Emit a bug report.
106 if (!BT_NullReference)
107 BT_NullReference.reset(new BuiltinBug("Returning null reference"));
108
109 emitBug(C, *BT_NullReference, RetE, bugreporter::getDerefExpr(RetE));
110 }
111
registerReturnUndefChecker(CheckerManager & mgr)112 void ento::registerReturnUndefChecker(CheckerManager &mgr) {
113 mgr.registerChecker<ReturnUndefChecker>();
114 }
115