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 
38 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 
85 void ento::registerObjCAtSyncChecker(CheckerManager &mgr) {
86   mgr.registerChecker<ObjCAtSyncChecker>();
87 }
88 
89 bool ento::shouldRegisterObjCAtSyncChecker(const CheckerManager &mgr) {
90   const LangOptions &LO = mgr.getLangOpts();
91   return LO.ObjC;
92 }
93