1 //===-- SimpleStreamChecker.cpp -----------------------------------------*- 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 // Defines a checker for proper use of fopen/fclose APIs.
10 //   - If a file has been closed with fclose, it should not be accessed again.
11 //   Accessing a closed file results in undefined behavior.
12 //   - If a file was opened with fopen, it must be closed with fclose before
13 //   the execution ends. Failing to do so results in a resource leak.
14 //
15 //===----------------------------------------------------------------------===//
16 
17 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
18 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
19 #include "clang/StaticAnalyzer/Core/Checker.h"
20 #include "clang/StaticAnalyzer/Core/PathSensitive/CallDescription.h"
21 #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
22 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
23 #include <utility>
24 
25 using namespace clang;
26 using namespace ento;
27 
28 namespace {
29 typedef SmallVector<SymbolRef, 2> SymbolVector;
30 
31 struct StreamState {
32 private:
33   enum Kind { Opened, Closed } K;
34   StreamState(Kind InK) : K(InK) { }
35 
36 public:
37   bool isOpened() const { return K == Opened; }
38   bool isClosed() const { return K == Closed; }
39 
40   static StreamState getOpened() { return StreamState(Opened); }
41   static StreamState getClosed() { return StreamState(Closed); }
42 
43   bool operator==(const StreamState &X) const {
44     return K == X.K;
45   }
46   void Profile(llvm::FoldingSetNodeID &ID) const {
47     ID.AddInteger(K);
48   }
49 };
50 
51 class SimpleStreamChecker : public Checker<check::PostCall,
52                                            check::PreCall,
53                                            check::DeadSymbols,
54                                            check::PointerEscape> {
55   CallDescription OpenFn, CloseFn;
56 
57   std::unique_ptr<BugType> DoubleCloseBugType;
58   std::unique_ptr<BugType> LeakBugType;
59 
60   void reportDoubleClose(SymbolRef FileDescSym,
61                          const CallEvent &Call,
62                          CheckerContext &C) const;
63 
64   void reportLeaks(ArrayRef<SymbolRef> LeakedStreams, CheckerContext &C,
65                    ExplodedNode *ErrNode) const;
66 
67   bool guaranteedNotToCloseFile(const CallEvent &Call) const;
68 
69 public:
70   SimpleStreamChecker();
71 
72   /// Process fopen.
73   void checkPostCall(const CallEvent &Call, CheckerContext &C) const;
74   /// Process fclose.
75   void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
76 
77   void checkDeadSymbols(SymbolReaper &SymReaper, CheckerContext &C) const;
78 
79   /// Stop tracking addresses which escape.
80   ProgramStateRef checkPointerEscape(ProgramStateRef State,
81                                     const InvalidatedSymbols &Escaped,
82                                     const CallEvent *Call,
83                                     PointerEscapeKind Kind) const;
84 };
85 
86 } // end anonymous namespace
87 
88 /// The state of the checker is a map from tracked stream symbols to their
89 /// state. Let's store it in the ProgramState.
90 REGISTER_MAP_WITH_PROGRAMSTATE(StreamMap, SymbolRef, StreamState)
91 
92 SimpleStreamChecker::SimpleStreamChecker()
93     : OpenFn({"fopen"}), CloseFn({"fclose"}, 1) {
94   // Initialize the bug types.
95   DoubleCloseBugType.reset(
96       new BugType(this, "Double fclose", "Unix Stream API Error"));
97 
98   // Sinks are higher importance bugs as well as calls to assert() or exit(0).
99   LeakBugType.reset(
100       new BugType(this, "Resource Leak", "Unix Stream API Error",
101                   /*SuppressOnSink=*/true));
102 }
103 
104 void SimpleStreamChecker::checkPostCall(const CallEvent &Call,
105                                         CheckerContext &C) const {
106   if (!Call.isGlobalCFunction())
107     return;
108 
109   if (!OpenFn.matches(Call))
110     return;
111 
112   // Get the symbolic value corresponding to the file handle.
113   SymbolRef FileDesc = Call.getReturnValue().getAsSymbol();
114   if (!FileDesc)
115     return;
116 
117   // Generate the next transition (an edge in the exploded graph).
118   ProgramStateRef State = C.getState();
119   State = State->set<StreamMap>(FileDesc, StreamState::getOpened());
120   C.addTransition(State);
121 }
122 
123 void SimpleStreamChecker::checkPreCall(const CallEvent &Call,
124                                        CheckerContext &C) const {
125   if (!Call.isGlobalCFunction())
126     return;
127 
128   if (!CloseFn.matches(Call))
129     return;
130 
131   // Get the symbolic value corresponding to the file handle.
132   SymbolRef FileDesc = Call.getArgSVal(0).getAsSymbol();
133   if (!FileDesc)
134     return;
135 
136   // Check if the stream has already been closed.
137   ProgramStateRef State = C.getState();
138   const StreamState *SS = State->get<StreamMap>(FileDesc);
139   if (SS && SS->isClosed()) {
140     reportDoubleClose(FileDesc, Call, C);
141     return;
142   }
143 
144   // Generate the next transition, in which the stream is closed.
145   State = State->set<StreamMap>(FileDesc, StreamState::getClosed());
146   C.addTransition(State);
147 }
148 
149 static bool isLeaked(SymbolRef Sym, const StreamState &SS,
150                      bool IsSymDead, ProgramStateRef State) {
151   if (IsSymDead && SS.isOpened()) {
152     // If a symbol is NULL, assume that fopen failed on this path.
153     // A symbol should only be considered leaked if it is non-null.
154     ConstraintManager &CMgr = State->getConstraintManager();
155     ConditionTruthVal OpenFailed = CMgr.isNull(State, Sym);
156     return !OpenFailed.isConstrainedTrue();
157   }
158   return false;
159 }
160 
161 void SimpleStreamChecker::checkDeadSymbols(SymbolReaper &SymReaper,
162                                            CheckerContext &C) const {
163   ProgramStateRef State = C.getState();
164   SymbolVector LeakedStreams;
165   StreamMapTy TrackedStreams = State->get<StreamMap>();
166   for (StreamMapTy::iterator I = TrackedStreams.begin(),
167                              E = TrackedStreams.end(); I != E; ++I) {
168     SymbolRef Sym = I->first;
169     bool IsSymDead = SymReaper.isDead(Sym);
170 
171     // Collect leaked symbols.
172     if (isLeaked(Sym, I->second, IsSymDead, State))
173       LeakedStreams.push_back(Sym);
174 
175     // Remove the dead symbol from the streams map.
176     if (IsSymDead)
177       State = State->remove<StreamMap>(Sym);
178   }
179 
180   ExplodedNode *N = C.generateNonFatalErrorNode(State);
181   if (!N)
182     return;
183   reportLeaks(LeakedStreams, C, N);
184 }
185 
186 void SimpleStreamChecker::reportDoubleClose(SymbolRef FileDescSym,
187                                             const CallEvent &Call,
188                                             CheckerContext &C) const {
189   // We reached a bug, stop exploring the path here by generating a sink.
190   ExplodedNode *ErrNode = C.generateErrorNode();
191   // If we've already reached this node on another path, return.
192   if (!ErrNode)
193     return;
194 
195   // Generate the report.
196   auto R = std::make_unique<PathSensitiveBugReport>(
197       *DoubleCloseBugType, "Closing a previously closed file stream", ErrNode);
198   R->addRange(Call.getSourceRange());
199   R->markInteresting(FileDescSym);
200   C.emitReport(std::move(R));
201 }
202 
203 void SimpleStreamChecker::reportLeaks(ArrayRef<SymbolRef> LeakedStreams,
204                                       CheckerContext &C,
205                                       ExplodedNode *ErrNode) const {
206   // Attach bug reports to the leak node.
207   // TODO: Identify the leaked file descriptor.
208   for (SymbolRef LeakedStream : LeakedStreams) {
209     auto R = std::make_unique<PathSensitiveBugReport>(
210         *LeakBugType, "Opened file is never closed; potential resource leak",
211         ErrNode);
212     R->markInteresting(LeakedStream);
213     C.emitReport(std::move(R));
214   }
215 }
216 
217 bool SimpleStreamChecker::guaranteedNotToCloseFile(const CallEvent &Call) const{
218   // If it's not in a system header, assume it might close a file.
219   if (!Call.isInSystemHeader())
220     return false;
221 
222   // Handle cases where we know a buffer's /address/ can escape.
223   if (Call.argumentsMayEscape())
224     return false;
225 
226   // Note, even though fclose closes the file, we do not list it here
227   // since the checker is modeling the call.
228 
229   return true;
230 }
231 
232 // If the pointer we are tracking escaped, do not track the symbol as
233 // we cannot reason about it anymore.
234 ProgramStateRef
235 SimpleStreamChecker::checkPointerEscape(ProgramStateRef State,
236                                         const InvalidatedSymbols &Escaped,
237                                         const CallEvent *Call,
238                                         PointerEscapeKind Kind) const {
239   // If we know that the call cannot close a file, there is nothing to do.
240   if (Kind == PSK_DirectEscapeOnCall && guaranteedNotToCloseFile(*Call)) {
241     return State;
242   }
243 
244   for (InvalidatedSymbols::const_iterator I = Escaped.begin(),
245                                           E = Escaped.end();
246                                           I != E; ++I) {
247     SymbolRef Sym = *I;
248 
249     // The symbol escaped. Optimistically, assume that the corresponding file
250     // handle will be closed somewhere else.
251     State = State->remove<StreamMap>(Sym);
252   }
253   return State;
254 }
255 
256 void ento::registerSimpleStreamChecker(CheckerManager &mgr) {
257   mgr.registerChecker<SimpleStreamChecker>();
258 }
259 
260 // This checker should be enabled regardless of how language options are set.
261 bool ento::shouldRegisterSimpleStreamChecker(const CheckerManager &mgr) {
262   return true;
263 }
264