1//===-- SimpleStreamChecker.cpp -----------------------------------------*- 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// Defines a checker for proper use of fopen/fclose APIs.
11//   - If a file has been closed with fclose, it should not be accessed again.
12//   Accessing a closed file results in undefined behavior.
13//   - If a file was opened with fopen, it must be closed with fclose before
14//   the execution ends. Failing to do so results in a resource leak.
15//
16//===----------------------------------------------------------------------===//
17
18#include "ClangSACheckers.h"
19#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
20#include "clang/StaticAnalyzer/Core/Checker.h"
21#include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
22#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
23
24using namespace clang;
25using namespace ento;
26
27namespace {
28typedef SmallVector<SymbolRef, 2> SymbolVector;
29
30struct StreamState {
31private:
32  enum Kind { Opened, Closed } K;
33  StreamState(Kind InK) : K(InK) { }
34
35public:
36  bool isOpened() const { return K == Opened; }
37  bool isClosed() const { return K == Closed; }
38
39  static StreamState getOpened() { return StreamState(Opened); }
40  static StreamState getClosed() { return StreamState(Closed); }
41
42  bool operator==(const StreamState &X) const {
43    return K == X.K;
44  }
45  void Profile(llvm::FoldingSetNodeID &ID) const {
46    ID.AddInteger(K);
47  }
48};
49
50class SimpleStreamChecker : public Checker<check::PostCall,
51                                           check::PreCall,
52                                           check::DeadSymbols,
53                                           check::PointerEscape> {
54
55  mutable IdentifierInfo *IIfopen, *IIfclose;
56
57  std::unique_ptr<BugType> DoubleCloseBugType;
58  std::unique_ptr<BugType> LeakBugType;
59
60  void initIdentifierInfo(ASTContext &Ctx) const;
61
62  void reportDoubleClose(SymbolRef FileDescSym,
63                         const CallEvent &Call,
64                         CheckerContext &C) const;
65
66  void reportLeaks(SymbolVector LeakedStreams,
67                   CheckerContext &C,
68                   ExplodedNode *ErrNode) const;
69
70  bool guaranteedNotToCloseFile(const CallEvent &Call) const;
71
72public:
73  SimpleStreamChecker();
74
75  /// Process fopen.
76  void checkPostCall(const CallEvent &Call, CheckerContext &C) const;
77  /// Process fclose.
78  void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
79
80  void checkDeadSymbols(SymbolReaper &SymReaper, CheckerContext &C) const;
81
82  /// Stop tracking addresses which escape.
83  ProgramStateRef checkPointerEscape(ProgramStateRef State,
84                                    const InvalidatedSymbols &Escaped,
85                                    const CallEvent *Call,
86                                    PointerEscapeKind Kind) const;
87};
88
89} // end anonymous namespace
90
91/// The state of the checker is a map from tracked stream symbols to their
92/// state. Let's store it in the ProgramState.
93REGISTER_MAP_WITH_PROGRAMSTATE(StreamMap, SymbolRef, StreamState)
94
95namespace {
96class StopTrackingCallback : public SymbolVisitor {
97  ProgramStateRef state;
98public:
99  StopTrackingCallback(ProgramStateRef st) : state(st) {}
100  ProgramStateRef getState() const { return state; }
101
102  bool VisitSymbol(SymbolRef sym) override {
103    state = state->remove<StreamMap>(sym);
104    return true;
105  }
106};
107} // end anonymous namespace
108
109SimpleStreamChecker::SimpleStreamChecker()
110    : IIfopen(nullptr), IIfclose(nullptr) {
111  // Initialize the bug types.
112  DoubleCloseBugType.reset(
113      new BugType(this, "Double fclose", "Unix Stream API Error"));
114
115  LeakBugType.reset(
116      new BugType(this, "Resource Leak", "Unix Stream API Error"));
117  // Sinks are higher importance bugs as well as calls to assert() or exit(0).
118  LeakBugType->setSuppressOnSink(true);
119}
120
121void SimpleStreamChecker::checkPostCall(const CallEvent &Call,
122                                        CheckerContext &C) const {
123  initIdentifierInfo(C.getASTContext());
124
125  if (!Call.isGlobalCFunction())
126    return;
127
128  if (Call.getCalleeIdentifier() != IIfopen)
129    return;
130
131  // Get the symbolic value corresponding to the file handle.
132  SymbolRef FileDesc = Call.getReturnValue().getAsSymbol();
133  if (!FileDesc)
134    return;
135
136  // Generate the next transition (an edge in the exploded graph).
137  ProgramStateRef State = C.getState();
138  State = State->set<StreamMap>(FileDesc, StreamState::getOpened());
139  C.addTransition(State);
140}
141
142void SimpleStreamChecker::checkPreCall(const CallEvent &Call,
143                                       CheckerContext &C) const {
144  initIdentifierInfo(C.getASTContext());
145
146  if (!Call.isGlobalCFunction())
147    return;
148
149  if (Call.getCalleeIdentifier() != IIfclose)
150    return;
151
152  if (Call.getNumArgs() != 1)
153    return;
154
155  // Get the symbolic value corresponding to the file handle.
156  SymbolRef FileDesc = Call.getArgSVal(0).getAsSymbol();
157  if (!FileDesc)
158    return;
159
160  // Check if the stream has already been closed.
161  ProgramStateRef State = C.getState();
162  const StreamState *SS = State->get<StreamMap>(FileDesc);
163  if (SS && SS->isClosed()) {
164    reportDoubleClose(FileDesc, Call, C);
165    return;
166  }
167
168  // Generate the next transition, in which the stream is closed.
169  State = State->set<StreamMap>(FileDesc, StreamState::getClosed());
170  C.addTransition(State);
171}
172
173static bool isLeaked(SymbolRef Sym, const StreamState &SS,
174                     bool IsSymDead, ProgramStateRef State) {
175  if (IsSymDead && SS.isOpened()) {
176    // If a symbol is NULL, assume that fopen failed on this path.
177    // A symbol should only be considered leaked if it is non-null.
178    ConstraintManager &CMgr = State->getConstraintManager();
179    ConditionTruthVal OpenFailed = CMgr.isNull(State, Sym);
180    return !OpenFailed.isConstrainedTrue();
181  }
182  return false;
183}
184
185void SimpleStreamChecker::checkDeadSymbols(SymbolReaper &SymReaper,
186                                           CheckerContext &C) const {
187  ProgramStateRef State = C.getState();
188  SymbolVector LeakedStreams;
189  StreamMapTy TrackedStreams = State->get<StreamMap>();
190  for (StreamMapTy::iterator I = TrackedStreams.begin(),
191                             E = TrackedStreams.end(); I != E; ++I) {
192    SymbolRef Sym = I->first;
193    bool IsSymDead = SymReaper.isDead(Sym);
194
195    // Collect leaked symbols.
196    if (isLeaked(Sym, I->second, IsSymDead, State))
197      LeakedStreams.push_back(Sym);
198
199    // Remove the dead symbol from the streams map.
200    if (IsSymDead)
201      State = State->remove<StreamMap>(Sym);
202  }
203
204  ExplodedNode *N = C.addTransition(State);
205  reportLeaks(LeakedStreams, C, N);
206}
207
208void SimpleStreamChecker::reportDoubleClose(SymbolRef FileDescSym,
209                                            const CallEvent &Call,
210                                            CheckerContext &C) const {
211  // We reached a bug, stop exploring the path here by generating a sink.
212  ExplodedNode *ErrNode = C.generateSink();
213  // If we've already reached this node on another path, return.
214  if (!ErrNode)
215    return;
216
217  // Generate the report.
218  BugReport *R = new BugReport(*DoubleCloseBugType,
219      "Closing a previously closed file stream", ErrNode);
220  R->addRange(Call.getSourceRange());
221  R->markInteresting(FileDescSym);
222  C.emitReport(R);
223}
224
225void SimpleStreamChecker::reportLeaks(SymbolVector LeakedStreams,
226                                               CheckerContext &C,
227                                               ExplodedNode *ErrNode) const {
228  // Attach bug reports to the leak node.
229  // TODO: Identify the leaked file descriptor.
230  for (SmallVectorImpl<SymbolRef>::iterator
231         I = LeakedStreams.begin(), E = LeakedStreams.end(); I != E; ++I) {
232    BugReport *R = new BugReport(*LeakBugType,
233        "Opened file is never closed; potential resource leak", ErrNode);
234    R->markInteresting(*I);
235    C.emitReport(R);
236  }
237}
238
239bool SimpleStreamChecker::guaranteedNotToCloseFile(const CallEvent &Call) const{
240  // If it's not in a system header, assume it might close a file.
241  if (!Call.isInSystemHeader())
242    return false;
243
244  // Handle cases where we know a buffer's /address/ can escape.
245  if (Call.argumentsMayEscape())
246    return false;
247
248  // Note, even though fclose closes the file, we do not list it here
249  // since the checker is modeling the call.
250
251  return true;
252}
253
254// If the pointer we are tracking escaped, do not track the symbol as
255// we cannot reason about it anymore.
256ProgramStateRef
257SimpleStreamChecker::checkPointerEscape(ProgramStateRef State,
258                                        const InvalidatedSymbols &Escaped,
259                                        const CallEvent *Call,
260                                        PointerEscapeKind Kind) const {
261  // If we know that the call cannot close a file, there is nothing to do.
262  if (Kind == PSK_DirectEscapeOnCall && guaranteedNotToCloseFile(*Call)) {
263    return State;
264  }
265
266  for (InvalidatedSymbols::const_iterator I = Escaped.begin(),
267                                          E = Escaped.end();
268                                          I != E; ++I) {
269    SymbolRef Sym = *I;
270
271    // The symbol escaped. Optimistically, assume that the corresponding file
272    // handle will be closed somewhere else.
273    State = State->remove<StreamMap>(Sym);
274  }
275  return State;
276}
277
278void SimpleStreamChecker::initIdentifierInfo(ASTContext &Ctx) const {
279  if (IIfopen)
280    return;
281  IIfopen = &Ctx.Idents.get("fopen");
282  IIfclose = &Ctx.Idents.get("fclose");
283}
284
285void ento::registerSimpleStreamChecker(CheckerManager &mgr) {
286  mgr.registerChecker<SimpleStreamChecker>();
287}
288