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