1 //== ObjCAtSyncChecker.cpp - nil mutex checker for @synchronized -*- 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 ObjCAtSyncChecker, a builtin check that checks for null pointers
10 // used as mutexes for @synchronized.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
15 #include "clang/AST/StmtObjC.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 "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
21
22 using namespace clang;
23 using namespace ento;
24
25 namespace {
26 class ObjCAtSyncChecker
27 : public Checker< check::PreStmt<ObjCAtSynchronizedStmt> > {
28 const BugType BT_null{this, "Nil value used as mutex for @synchronized() "
29 "(no synchronization will occur)"};
30 const BugType BT_undef{this, "Uninitialized value used as mutex "
31 "for @synchronized"};
32
33 public:
34 void checkPreStmt(const ObjCAtSynchronizedStmt *S, CheckerContext &C) const;
35 };
36 } // end anonymous namespace
37
checkPreStmt(const ObjCAtSynchronizedStmt * S,CheckerContext & C) const38 void ObjCAtSyncChecker::checkPreStmt(const ObjCAtSynchronizedStmt *S,
39 CheckerContext &C) const {
40
41 const Expr *Ex = S->getSynchExpr();
42 ProgramStateRef state = C.getState();
43 SVal V = C.getSVal(Ex);
44
45 // Uninitialized value used for the mutex?
46 if (isa<UndefinedVal>(V)) {
47 if (ExplodedNode *N = C.generateErrorNode()) {
48 auto report = std::make_unique<PathSensitiveBugReport>(
49 BT_undef, BT_undef.getDescription(), N);
50 bugreporter::trackExpressionValue(N, Ex, *report);
51 C.emitReport(std::move(report));
52 }
53 return;
54 }
55
56 if (V.isUnknown())
57 return;
58
59 // Check for null mutexes.
60 ProgramStateRef notNullState, nullState;
61 std::tie(notNullState, nullState) = state->assume(V.castAs<DefinedSVal>());
62
63 if (nullState) {
64 if (!notNullState) {
65 // Generate an error node. This isn't a sink since
66 // a null mutex just means no synchronization occurs.
67 if (ExplodedNode *N = C.generateNonFatalErrorNode(nullState)) {
68 auto report = std::make_unique<PathSensitiveBugReport>(
69 BT_null, BT_null.getDescription(), N);
70 bugreporter::trackExpressionValue(N, Ex, *report);
71
72 C.emitReport(std::move(report));
73 return;
74 }
75 }
76 // Don't add a transition for 'nullState'. If the value is
77 // under-constrained to be null or non-null, assume it is non-null
78 // afterwards.
79 }
80
81 if (notNullState)
82 C.addTransition(notNullState);
83 }
84
registerObjCAtSyncChecker(CheckerManager & mgr)85 void ento::registerObjCAtSyncChecker(CheckerManager &mgr) {
86 mgr.registerChecker<ObjCAtSyncChecker>();
87 }
88
shouldRegisterObjCAtSyncChecker(const CheckerManager & mgr)89 bool ento::shouldRegisterObjCAtSyncChecker(const CheckerManager &mgr) {
90 const LangOptions &LO = mgr.getLangOpts();
91 return LO.ObjC;
92 }
93