1 //== ReturnUndefChecker.cpp -------------------------------------*- 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 file defines ReturnUndefChecker, which is a path-sensitive
10 // check which looks for undefined or garbage values being returned to the
11 // caller.
12 //
13 //===----------------------------------------------------------------------===//
14
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/CallEvent.h"
20 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
21
22 using namespace clang;
23 using namespace ento;
24
25 namespace {
26 class ReturnUndefChecker : public Checker< check::PreStmt<ReturnStmt> > {
27 const BugType BT_Undef{this, "Garbage return value"};
28 const BugType BT_NullReference{this, "Returning null reference"};
29
30 void emitUndef(CheckerContext &C, const Expr *RetE) const;
31 void checkReference(CheckerContext &C, const Expr *RetE,
32 DefinedOrUnknownSVal RetVal) const;
33 public:
34 void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const;
35 };
36 }
37
checkPreStmt(const ReturnStmt * RS,CheckerContext & C) const38 void ReturnUndefChecker::checkPreStmt(const ReturnStmt *RS,
39 CheckerContext &C) const {
40 const Expr *RetE = RS->getRetValue();
41 if (!RetE)
42 return;
43 SVal RetVal = C.getSVal(RetE);
44
45 const StackFrameContext *SFC = C.getStackFrame();
46 QualType RT = CallEvent::getDeclaredResultType(SFC->getDecl());
47
48 if (RetVal.isUndef()) {
49 // "return;" is modeled to evaluate to an UndefinedVal. Allow UndefinedVal
50 // to be returned in functions returning void to support this pattern:
51 // void foo() {
52 // return;
53 // }
54 // void test() {
55 // return foo();
56 // }
57 if (!RT.isNull() && RT->isVoidType())
58 return;
59
60 // Not all blocks have explicitly-specified return types; if the return type
61 // is not available, but the return value expression has 'void' type, assume
62 // Sema already checked it.
63 if (RT.isNull() && isa<BlockDecl>(SFC->getDecl()) &&
64 RetE->getType()->isVoidType())
65 return;
66
67 emitUndef(C, RetE);
68 return;
69 }
70
71 if (RT.isNull())
72 return;
73
74 if (RT->isReferenceType()) {
75 checkReference(C, RetE, RetVal.castAs<DefinedOrUnknownSVal>());
76 return;
77 }
78 }
79
emitBug(CheckerContext & C,const BugType & BT,StringRef Msg,const Expr * RetE,const Expr * TrackingE=nullptr)80 static void emitBug(CheckerContext &C, const BugType &BT, StringRef Msg,
81 const Expr *RetE, const Expr *TrackingE = nullptr) {
82 ExplodedNode *N = C.generateErrorNode();
83 if (!N)
84 return;
85
86 auto Report = std::make_unique<PathSensitiveBugReport>(BT, Msg, N);
87
88 Report->addRange(RetE->getSourceRange());
89 bugreporter::trackExpressionValue(N, TrackingE ? TrackingE : RetE, *Report);
90
91 C.emitReport(std::move(Report));
92 }
93
emitUndef(CheckerContext & C,const Expr * RetE) const94 void ReturnUndefChecker::emitUndef(CheckerContext &C, const Expr *RetE) const {
95 emitBug(C, BT_Undef, "Undefined or garbage value returned to caller", RetE);
96 }
97
checkReference(CheckerContext & C,const Expr * RetE,DefinedOrUnknownSVal RetVal) const98 void ReturnUndefChecker::checkReference(CheckerContext &C, const Expr *RetE,
99 DefinedOrUnknownSVal RetVal) const {
100 ProgramStateRef StNonNull, StNull;
101 std::tie(StNonNull, StNull) = C.getState()->assume(RetVal);
102
103 if (StNonNull) {
104 // Going forward, assume the location is non-null.
105 C.addTransition(StNonNull);
106 return;
107 }
108
109 // The return value is known to be null. Emit a bug report.
110 emitBug(C, BT_NullReference, BT_NullReference.getDescription(), RetE,
111 bugreporter::getDerefExpr(RetE));
112 }
113
registerReturnUndefChecker(CheckerManager & mgr)114 void ento::registerReturnUndefChecker(CheckerManager &mgr) {
115 mgr.registerChecker<ReturnUndefChecker>();
116 }
117
shouldRegisterReturnUndefChecker(const CheckerManager & mgr)118 bool ento::shouldRegisterReturnUndefChecker(const CheckerManager &mgr) {
119 return true;
120 }
121