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1 //== ObjCAtSyncChecker.cpp - nil mutex checker for @synchronized -*- 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 defines ObjCAtSyncChecker, a builtin check that checks for null pointers
11 // used as mutexes for @synchronized.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #include "ClangSACheckers.h"
16 #include "clang/StaticAnalyzer/Core/Checker.h"
17 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
18 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
19 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
20 #include "clang/StaticAnalyzer/Checkers/DereferenceChecker.h"
21 #include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
22 
23 using namespace clang;
24 using namespace ento;
25 
26 namespace {
27 class ObjCAtSyncChecker
28     : public Checker< check::PreStmt<ObjCAtSynchronizedStmt> > {
29   mutable llvm::OwningPtr<BuiltinBug> BT_null;
30   mutable llvm::OwningPtr<BuiltinBug> BT_undef;
31 
32 public:
33   void checkPreStmt(const ObjCAtSynchronizedStmt *S, CheckerContext &C) const;
34 };
35 } // end anonymous namespace
36 
checkPreStmt(const ObjCAtSynchronizedStmt * S,CheckerContext & C) const37 void ObjCAtSyncChecker::checkPreStmt(const ObjCAtSynchronizedStmt *S,
38                                      CheckerContext &C) const {
39 
40   const Expr *Ex = S->getSynchExpr();
41   const GRState *state = C.getState();
42   SVal V = state->getSVal(Ex);
43 
44   // Uninitialized value used for the mutex?
45   if (isa<UndefinedVal>(V)) {
46     if (ExplodedNode *N = C.generateSink()) {
47       if (!BT_undef)
48         BT_undef.reset(new BuiltinBug("Uninitialized value used as mutex "
49                                   "for @synchronized"));
50       EnhancedBugReport *report =
51         new EnhancedBugReport(*BT_undef, BT_undef->getDescription(), N);
52       report->addVisitorCreator(bugreporter::registerTrackNullOrUndefValue, Ex);
53       C.EmitReport(report);
54     }
55     return;
56   }
57 
58   if (V.isUnknown())
59     return;
60 
61   // Check for null mutexes.
62   const GRState *notNullState, *nullState;
63   llvm::tie(notNullState, nullState) = state->assume(cast<DefinedSVal>(V));
64 
65   if (nullState) {
66     if (!notNullState) {
67       // Generate an error node.  This isn't a sink since
68       // a null mutex just means no synchronization occurs.
69       if (ExplodedNode *N = C.generateNode(nullState)) {
70         if (!BT_null)
71           BT_null.reset(new BuiltinBug("Nil value used as mutex for @synchronized() "
72                                    "(no synchronization will occur)"));
73         EnhancedBugReport *report =
74           new EnhancedBugReport(*BT_null, BT_null->getDescription(), N);
75         report->addVisitorCreator(bugreporter::registerTrackNullOrUndefValue,
76                                   Ex);
77 
78         C.EmitReport(report);
79         return;
80       }
81     }
82     // Don't add a transition for 'nullState'.  If the value is
83     // under-constrained to be null or non-null, assume it is non-null
84     // afterwards.
85   }
86 
87   if (notNullState)
88     C.addTransition(notNullState);
89 }
90 
registerObjCAtSyncChecker(CheckerManager & mgr)91 void ento::registerObjCAtSyncChecker(CheckerManager &mgr) {
92   if (mgr.getLangOptions().ObjC2)
93     mgr.registerChecker<ObjCAtSyncChecker>();
94 }
95