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1 //=- NSErrorChecker.cpp - Coding conventions for uses of NSError -*- 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 file defines a CheckNSError, a flow-insenstive check
11 //  that determines if an Objective-C class interface correctly returns
12 //  a non-void return type.
13 //
14 //  File under feature request PR 2600.
15 //
16 //===----------------------------------------------------------------------===//
17 
18 #include "ClangSACheckers.h"
19 #include "clang/AST/Decl.h"
20 #include "clang/AST/DeclObjC.h"
21 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
22 #include "clang/StaticAnalyzer/Core/Checker.h"
23 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
24 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
25 #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramStateTrait.h"
26 #include "llvm/ADT/SmallString.h"
27 #include "llvm/Support/raw_ostream.h"
28 
29 using namespace clang;
30 using namespace ento;
31 
32 static bool IsNSError(QualType T, IdentifierInfo *II);
33 static bool IsCFError(QualType T, IdentifierInfo *II);
34 
35 //===----------------------------------------------------------------------===//
36 // NSErrorMethodChecker
37 //===----------------------------------------------------------------------===//
38 
39 namespace {
40 class NSErrorMethodChecker
41     : public Checker< check::ASTDecl<ObjCMethodDecl> > {
42   mutable IdentifierInfo *II;
43 
44 public:
NSErrorMethodChecker()45   NSErrorMethodChecker() : II(nullptr) {}
46 
47   void checkASTDecl(const ObjCMethodDecl *D,
48                     AnalysisManager &mgr, BugReporter &BR) const;
49 };
50 }
51 
checkASTDecl(const ObjCMethodDecl * D,AnalysisManager & mgr,BugReporter & BR) const52 void NSErrorMethodChecker::checkASTDecl(const ObjCMethodDecl *D,
53                                         AnalysisManager &mgr,
54                                         BugReporter &BR) const {
55   if (!D->isThisDeclarationADefinition())
56     return;
57   if (!D->getReturnType()->isVoidType())
58     return;
59 
60   if (!II)
61     II = &D->getASTContext().Idents.get("NSError");
62 
63   bool hasNSError = false;
64   for (const auto *I : D->parameters())  {
65     if (IsNSError(I->getType(), II)) {
66       hasNSError = true;
67       break;
68     }
69   }
70 
71   if (hasNSError) {
72     const char *err = "Method accepting NSError** "
73         "should have a non-void return value to indicate whether or not an "
74         "error occurred";
75     PathDiagnosticLocation L =
76       PathDiagnosticLocation::create(D, BR.getSourceManager());
77     BR.EmitBasicReport(D, this, "Bad return type when passing NSError**",
78                        "Coding conventions (Apple)", err, L);
79   }
80 }
81 
82 //===----------------------------------------------------------------------===//
83 // CFErrorFunctionChecker
84 //===----------------------------------------------------------------------===//
85 
86 namespace {
87 class CFErrorFunctionChecker
88     : public Checker< check::ASTDecl<FunctionDecl> > {
89   mutable IdentifierInfo *II;
90 
91 public:
CFErrorFunctionChecker()92   CFErrorFunctionChecker() : II(nullptr) {}
93 
94   void checkASTDecl(const FunctionDecl *D,
95                     AnalysisManager &mgr, BugReporter &BR) const;
96 };
97 }
98 
checkASTDecl(const FunctionDecl * D,AnalysisManager & mgr,BugReporter & BR) const99 void CFErrorFunctionChecker::checkASTDecl(const FunctionDecl *D,
100                                         AnalysisManager &mgr,
101                                         BugReporter &BR) const {
102   if (!D->doesThisDeclarationHaveABody())
103     return;
104   if (!D->getReturnType()->isVoidType())
105     return;
106 
107   if (!II)
108     II = &D->getASTContext().Idents.get("CFErrorRef");
109 
110   bool hasCFError = false;
111   for (auto I : D->parameters())  {
112     if (IsCFError(I->getType(), II)) {
113       hasCFError = true;
114       break;
115     }
116   }
117 
118   if (hasCFError) {
119     const char *err = "Function accepting CFErrorRef* "
120         "should have a non-void return value to indicate whether or not an "
121         "error occurred";
122     PathDiagnosticLocation L =
123       PathDiagnosticLocation::create(D, BR.getSourceManager());
124     BR.EmitBasicReport(D, this, "Bad return type when passing CFErrorRef*",
125                        "Coding conventions (Apple)", err, L);
126   }
127 }
128 
129 //===----------------------------------------------------------------------===//
130 // NSOrCFErrorDerefChecker
131 //===----------------------------------------------------------------------===//
132 
133 namespace {
134 
135 class NSErrorDerefBug : public BugType {
136 public:
NSErrorDerefBug(const CheckerBase * Checker)137   NSErrorDerefBug(const CheckerBase *Checker)
138       : BugType(Checker, "NSError** null dereference",
139                 "Coding conventions (Apple)") {}
140 };
141 
142 class CFErrorDerefBug : public BugType {
143 public:
CFErrorDerefBug(const CheckerBase * Checker)144   CFErrorDerefBug(const CheckerBase *Checker)
145       : BugType(Checker, "CFErrorRef* null dereference",
146                 "Coding conventions (Apple)") {}
147 };
148 
149 }
150 
151 namespace {
152 class NSOrCFErrorDerefChecker
153     : public Checker< check::Location,
154                         check::Event<ImplicitNullDerefEvent> > {
155   mutable IdentifierInfo *NSErrorII, *CFErrorII;
156   mutable std::unique_ptr<NSErrorDerefBug> NSBT;
157   mutable std::unique_ptr<CFErrorDerefBug> CFBT;
158 public:
159   bool ShouldCheckNSError, ShouldCheckCFError;
NSOrCFErrorDerefChecker()160   NSOrCFErrorDerefChecker() : NSErrorII(nullptr), CFErrorII(nullptr),
161                               ShouldCheckNSError(0), ShouldCheckCFError(0) { }
162 
163   void checkLocation(SVal loc, bool isLoad, const Stmt *S,
164                      CheckerContext &C) const;
165   void checkEvent(ImplicitNullDerefEvent event) const;
166 };
167 }
168 
169 typedef llvm::ImmutableMap<SymbolRef, unsigned> ErrorOutFlag;
REGISTER_TRAIT_WITH_PROGRAMSTATE(NSErrorOut,ErrorOutFlag)170 REGISTER_TRAIT_WITH_PROGRAMSTATE(NSErrorOut, ErrorOutFlag)
171 REGISTER_TRAIT_WITH_PROGRAMSTATE(CFErrorOut, ErrorOutFlag)
172 
173 template <typename T>
174 static bool hasFlag(SVal val, ProgramStateRef state) {
175   if (SymbolRef sym = val.getAsSymbol())
176     if (const unsigned *attachedFlags = state->get<T>(sym))
177       return *attachedFlags;
178   return false;
179 }
180 
181 template <typename T>
setFlag(ProgramStateRef state,SVal val,CheckerContext & C)182 static void setFlag(ProgramStateRef state, SVal val, CheckerContext &C) {
183   // We tag the symbol that the SVal wraps.
184   if (SymbolRef sym = val.getAsSymbol())
185     C.addTransition(state->set<T>(sym, true));
186 }
187 
parameterTypeFromSVal(SVal val,CheckerContext & C)188 static QualType parameterTypeFromSVal(SVal val, CheckerContext &C) {
189   const StackFrameContext *
190     SFC = C.getLocationContext()->getCurrentStackFrame();
191   if (Optional<loc::MemRegionVal> X = val.getAs<loc::MemRegionVal>()) {
192     const MemRegion* R = X->getRegion();
193     if (const VarRegion *VR = R->getAs<VarRegion>())
194       if (const StackArgumentsSpaceRegion *
195           stackReg = dyn_cast<StackArgumentsSpaceRegion>(VR->getMemorySpace()))
196         if (stackReg->getStackFrame() == SFC)
197           return VR->getValueType();
198   }
199 
200   return QualType();
201 }
202 
checkLocation(SVal loc,bool isLoad,const Stmt * S,CheckerContext & C) const203 void NSOrCFErrorDerefChecker::checkLocation(SVal loc, bool isLoad,
204                                             const Stmt *S,
205                                             CheckerContext &C) const {
206   if (!isLoad)
207     return;
208   if (loc.isUndef() || !loc.getAs<Loc>())
209     return;
210 
211   ASTContext &Ctx = C.getASTContext();
212   ProgramStateRef state = C.getState();
213 
214   // If we are loading from NSError**/CFErrorRef* parameter, mark the resulting
215   // SVal so that we can later check it when handling the
216   // ImplicitNullDerefEvent event.
217   // FIXME: Cumbersome! Maybe add hook at construction of SVals at start of
218   // function ?
219 
220   QualType parmT = parameterTypeFromSVal(loc, C);
221   if (parmT.isNull())
222     return;
223 
224   if (!NSErrorII)
225     NSErrorII = &Ctx.Idents.get("NSError");
226   if (!CFErrorII)
227     CFErrorII = &Ctx.Idents.get("CFErrorRef");
228 
229   if (ShouldCheckNSError && IsNSError(parmT, NSErrorII)) {
230     setFlag<NSErrorOut>(state, state->getSVal(loc.castAs<Loc>()), C);
231     return;
232   }
233 
234   if (ShouldCheckCFError && IsCFError(parmT, CFErrorII)) {
235     setFlag<CFErrorOut>(state, state->getSVal(loc.castAs<Loc>()), C);
236     return;
237   }
238 }
239 
checkEvent(ImplicitNullDerefEvent event) const240 void NSOrCFErrorDerefChecker::checkEvent(ImplicitNullDerefEvent event) const {
241   if (event.IsLoad)
242     return;
243 
244   SVal loc = event.Location;
245   ProgramStateRef state = event.SinkNode->getState();
246   BugReporter &BR = *event.BR;
247 
248   bool isNSError = hasFlag<NSErrorOut>(loc, state);
249   bool isCFError = false;
250   if (!isNSError)
251     isCFError = hasFlag<CFErrorOut>(loc, state);
252 
253   if (!(isNSError || isCFError))
254     return;
255 
256   // Storing to possible null NSError/CFErrorRef out parameter.
257   SmallString<128> Buf;
258   llvm::raw_svector_ostream os(Buf);
259 
260   os << "Potential null dereference.  According to coding standards ";
261   os << (isNSError
262          ? "in 'Creating and Returning NSError Objects' the parameter"
263          : "documented in CoreFoundation/CFError.h the parameter");
264 
265   os  << " may be null";
266 
267   BugType *bug = nullptr;
268   if (isNSError) {
269     if (!NSBT)
270       NSBT.reset(new NSErrorDerefBug(this));
271     bug = NSBT.get();
272   }
273   else {
274     if (!CFBT)
275       CFBT.reset(new CFErrorDerefBug(this));
276     bug = CFBT.get();
277   }
278   BR.emitReport(llvm::make_unique<BugReport>(*bug, os.str(), event.SinkNode));
279 }
280 
IsNSError(QualType T,IdentifierInfo * II)281 static bool IsNSError(QualType T, IdentifierInfo *II) {
282 
283   const PointerType* PPT = T->getAs<PointerType>();
284   if (!PPT)
285     return false;
286 
287   const ObjCObjectPointerType* PT =
288     PPT->getPointeeType()->getAs<ObjCObjectPointerType>();
289 
290   if (!PT)
291     return false;
292 
293   const ObjCInterfaceDecl *ID = PT->getInterfaceDecl();
294 
295   // FIXME: Can ID ever be NULL?
296   if (ID)
297     return II == ID->getIdentifier();
298 
299   return false;
300 }
301 
IsCFError(QualType T,IdentifierInfo * II)302 static bool IsCFError(QualType T, IdentifierInfo *II) {
303   const PointerType* PPT = T->getAs<PointerType>();
304   if (!PPT) return false;
305 
306   const TypedefType* TT = PPT->getPointeeType()->getAs<TypedefType>();
307   if (!TT) return false;
308 
309   return TT->getDecl()->getIdentifier() == II;
310 }
311 
registerNSErrorChecker(CheckerManager & mgr)312 void ento::registerNSErrorChecker(CheckerManager &mgr) {
313   mgr.registerChecker<NSErrorMethodChecker>();
314   NSOrCFErrorDerefChecker *checker =
315       mgr.registerChecker<NSOrCFErrorDerefChecker>();
316   checker->ShouldCheckNSError = true;
317 }
318 
registerCFErrorChecker(CheckerManager & mgr)319 void ento::registerCFErrorChecker(CheckerManager &mgr) {
320   mgr.registerChecker<CFErrorFunctionChecker>();
321   NSOrCFErrorDerefChecker *checker =
322       mgr.registerChecker<NSOrCFErrorDerefChecker>();
323   checker->ShouldCheckCFError = true;
324 }
325