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   mutable std::unique_ptr<BuiltinBug> BT_null;
29   mutable std::unique_ptr<BuiltinBug> BT_undef;
30 
31 public:
32   void checkPreStmt(const ObjCAtSynchronizedStmt *S, CheckerContext &C) const;
33 };
34 } // end anonymous namespace
35 
36 void ObjCAtSyncChecker::checkPreStmt(const ObjCAtSynchronizedStmt *S,
37                                      CheckerContext &C) const {
38 
39   const Expr *Ex = S->getSynchExpr();
40   ProgramStateRef state = C.getState();
41   SVal V = C.getSVal(Ex);
42 
43   // Uninitialized value used for the mutex?
44   if (isa<UndefinedVal>(V)) {
45     if (ExplodedNode *N = C.generateErrorNode()) {
46       if (!BT_undef)
47         BT_undef.reset(new BuiltinBug(this, "Uninitialized value used as mutex "
48                                             "for @synchronized"));
49       auto report = std::make_unique<PathSensitiveBugReport>(
50           *BT_undef, BT_undef->getDescription(), N);
51       bugreporter::trackExpressionValue(N, Ex, *report);
52       C.emitReport(std::move(report));
53     }
54     return;
55   }
56 
57   if (V.isUnknown())
58     return;
59 
60   // Check for null mutexes.
61   ProgramStateRef notNullState, nullState;
62   std::tie(notNullState, nullState) = state->assume(V.castAs<DefinedSVal>());
63 
64   if (nullState) {
65     if (!notNullState) {
66       // Generate an error node.  This isn't a sink since
67       // a null mutex just means no synchronization occurs.
68       if (ExplodedNode *N = C.generateNonFatalErrorNode(nullState)) {
69         if (!BT_null)
70           BT_null.reset(new BuiltinBug(
71               this, "Nil value used as mutex for @synchronized() "
72                     "(no synchronization will occur)"));
73         auto report = std::make_unique<PathSensitiveBugReport>(
74             *BT_null, BT_null->getDescription(), N);
75         bugreporter::trackExpressionValue(N, Ex, *report);
76 
77         C.emitReport(std::move(report));
78         return;
79       }
80     }
81     // Don't add a transition for 'nullState'.  If the value is
82     // under-constrained to be null or non-null, assume it is non-null
83     // afterwards.
84   }
85 
86   if (notNullState)
87     C.addTransition(notNullState);
88 }
89 
90 void ento::registerObjCAtSyncChecker(CheckerManager &mgr) {
91   mgr.registerChecker<ObjCAtSyncChecker>();
92 }
93 
94 bool ento::shouldRegisterObjCAtSyncChecker(const CheckerManager &mgr) {
95   const LangOptions &LO = mgr.getLangOpts();
96   return LO.ObjC;
97 }
98