1 //===--- NonNullParamChecker.cpp - Undefined arguments checker -*- 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 NonNullParamChecker, which checks for arguments expected not to
11 // be null due to:
12 //   - the corresponding parameters being declared to have nonnull attribute
13 //   - the corresponding parameters being references; since the call would form
14 //     a reference to a null pointer
15 //
16 //===----------------------------------------------------------------------===//
17 
18 #include "ClangSACheckers.h"
19 #include "clang/AST/Attr.h"
20 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
21 #include "clang/StaticAnalyzer/Core/Checker.h"
22 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
23 #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
24 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
25 
26 using namespace clang;
27 using namespace ento;
28 
29 namespace {
30 class NonNullParamChecker
31   : public Checker< check::PreCall, EventDispatcher<ImplicitNullDerefEvent> > {
32   mutable std::unique_ptr<BugType> BTAttrNonNull;
33   mutable std::unique_ptr<BugType> BTNullRefArg;
34 
35 public:
36 
37   void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
38 
39   std::unique_ptr<BugReport>
40   genReportNullAttrNonNull(const ExplodedNode *ErrorN, const Expr *ArgE) const;
41   std::unique_ptr<BugReport>
42   genReportReferenceToNullPointer(const ExplodedNode *ErrorN,
43                                   const Expr *ArgE) const;
44 };
45 } // end anonymous namespace
46 
47 void NonNullParamChecker::checkPreCall(const CallEvent &Call,
48                                        CheckerContext &C) const {
49   const Decl *FD = Call.getDecl();
50   if (!FD)
51     return;
52 
53   // Merge all non-null attributes
54   unsigned NumArgs = Call.getNumArgs();
55   llvm::SmallBitVector AttrNonNull(NumArgs);
56   for (const auto *NonNull : FD->specific_attrs<NonNullAttr>()) {
57     if (!NonNull->args_size()) {
58       AttrNonNull.set(0, NumArgs);
59       break;
60     }
61     for (const ParamIdx &Idx : NonNull->args()) {
62       unsigned IdxAST = Idx.getASTIndex();
63       if (IdxAST >= NumArgs)
64         continue;
65       AttrNonNull.set(IdxAST);
66     }
67   }
68 
69   ProgramStateRef state = C.getState();
70 
71   CallEvent::param_type_iterator TyI = Call.param_type_begin(),
72                                  TyE = Call.param_type_end();
73 
74   for (unsigned idx = 0; idx < NumArgs; ++idx) {
75 
76     // Check if the parameter is a reference. We want to report when reference
77     // to a null pointer is passed as a parameter.
78     bool haveRefTypeParam = false;
79     if (TyI != TyE) {
80       haveRefTypeParam = (*TyI)->isReferenceType();
81       TyI++;
82     }
83 
84     bool haveAttrNonNull = AttrNonNull[idx];
85     if (!haveAttrNonNull) {
86       // Check if the parameter is also marked 'nonnull'.
87       ArrayRef<ParmVarDecl*> parms = Call.parameters();
88       if (idx < parms.size())
89         haveAttrNonNull = parms[idx]->hasAttr<NonNullAttr>();
90     }
91 
92     if (!haveRefTypeParam && !haveAttrNonNull)
93       continue;
94 
95     // If the value is unknown or undefined, we can't perform this check.
96     const Expr *ArgE = Call.getArgExpr(idx);
97     SVal V = Call.getArgSVal(idx);
98     Optional<DefinedSVal> DV = V.getAs<DefinedSVal>();
99     if (!DV)
100       continue;
101 
102     // Process the case when the argument is not a location.
103     assert(!haveRefTypeParam || DV->getAs<Loc>());
104 
105     if (haveAttrNonNull && !DV->getAs<Loc>()) {
106       // If the argument is a union type, we want to handle a potential
107       // transparent_union GCC extension.
108       if (!ArgE)
109         continue;
110 
111       QualType T = ArgE->getType();
112       const RecordType *UT = T->getAsUnionType();
113       if (!UT || !UT->getDecl()->hasAttr<TransparentUnionAttr>())
114         continue;
115 
116       if (Optional<nonloc::CompoundVal> CSV =
117               DV->getAs<nonloc::CompoundVal>()) {
118         nonloc::CompoundVal::iterator CSV_I = CSV->begin();
119         assert(CSV_I != CSV->end());
120         V = *CSV_I;
121         DV = V.getAs<DefinedSVal>();
122         assert(++CSV_I == CSV->end());
123         // FIXME: Handle (some_union){ some_other_union_val }, which turns into
124         // a LazyCompoundVal inside a CompoundVal.
125         if (!V.getAs<Loc>())
126           continue;
127         // Retrieve the corresponding expression.
128         if (const CompoundLiteralExpr *CE = dyn_cast<CompoundLiteralExpr>(ArgE))
129           if (const InitListExpr *IE =
130                 dyn_cast<InitListExpr>(CE->getInitializer()))
131              ArgE = dyn_cast<Expr>(*(IE->begin()));
132 
133       } else {
134         // FIXME: Handle LazyCompoundVals?
135         continue;
136       }
137     }
138 
139     ConstraintManager &CM = C.getConstraintManager();
140     ProgramStateRef stateNotNull, stateNull;
141     std::tie(stateNotNull, stateNull) = CM.assumeDual(state, *DV);
142 
143     if (stateNull) {
144       if (!stateNotNull) {
145         // Generate an error node.  Check for a null node in case
146         // we cache out.
147         if (ExplodedNode *errorNode = C.generateErrorNode(stateNull)) {
148 
149           std::unique_ptr<BugReport> R;
150           if (haveAttrNonNull)
151             R = genReportNullAttrNonNull(errorNode, ArgE);
152           else if (haveRefTypeParam)
153             R = genReportReferenceToNullPointer(errorNode, ArgE);
154 
155           // Highlight the range of the argument that was null.
156           R->addRange(Call.getArgSourceRange(idx));
157 
158           // Emit the bug report.
159           C.emitReport(std::move(R));
160         }
161 
162         // Always return.  Either we cached out or we just emitted an error.
163         return;
164       }
165       if (ExplodedNode *N = C.generateSink(stateNull, C.getPredecessor())) {
166         ImplicitNullDerefEvent event = {
167             V, false, N, &C.getBugReporter(),
168             /*IsDirectDereference=*/haveRefTypeParam};
169         dispatchEvent(event);
170       }
171     }
172 
173     // If a pointer value passed the check we should assume that it is
174     // indeed not null from this point forward.
175     assert(stateNotNull);
176     state = stateNotNull;
177   }
178 
179   // If we reach here all of the arguments passed the nonnull check.
180   // If 'state' has been updated generated a new node.
181   C.addTransition(state);
182 }
183 
184 std::unique_ptr<BugReport>
185 NonNullParamChecker::genReportNullAttrNonNull(const ExplodedNode *ErrorNode,
186                                               const Expr *ArgE) const {
187   // Lazily allocate the BugType object if it hasn't already been
188   // created. Ownership is transferred to the BugReporter object once
189   // the BugReport is passed to 'EmitWarning'.
190   if (!BTAttrNonNull)
191     BTAttrNonNull.reset(new BugType(
192         this, "Argument with 'nonnull' attribute passed null", "API"));
193 
194   auto R = llvm::make_unique<BugReport>(
195       *BTAttrNonNull,
196       "Null pointer passed as an argument to a 'nonnull' parameter", ErrorNode);
197   if (ArgE)
198     bugreporter::trackNullOrUndefValue(ErrorNode, ArgE, *R);
199 
200   return R;
201 }
202 
203 std::unique_ptr<BugReport> NonNullParamChecker::genReportReferenceToNullPointer(
204     const ExplodedNode *ErrorNode, const Expr *ArgE) const {
205   if (!BTNullRefArg)
206     BTNullRefArg.reset(new BuiltinBug(this, "Dereference of null pointer"));
207 
208   auto R = llvm::make_unique<BugReport>(
209       *BTNullRefArg, "Forming reference to null pointer", ErrorNode);
210   if (ArgE) {
211     const Expr *ArgEDeref = bugreporter::getDerefExpr(ArgE);
212     if (!ArgEDeref)
213       ArgEDeref = ArgE;
214     bugreporter::trackNullOrUndefValue(ErrorNode,
215                                        ArgEDeref,
216                                        *R);
217   }
218   return R;
219 
220 }
221 
222 void ento::registerNonNullParamChecker(CheckerManager &mgr) {
223   mgr.registerChecker<NonNullParamChecker>();
224 }
225