1//== ValistChecker.cpp - stdarg.h macro usage checker -----------*- 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// This defines checkers which detect usage of uninitialized va_list values
10// and va_start calls with no matching va_end.
11//
12//===----------------------------------------------------------------------===//
13
14#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
15#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
16#include "clang/StaticAnalyzer/Core/Checker.h"
17#include "clang/StaticAnalyzer/Core/CheckerManager.h"
18#include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
19#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
20
21using namespace clang;
22using namespace ento;
23
24REGISTER_SET_WITH_PROGRAMSTATE(InitializedVALists, const MemRegion *)
25
26namespace {
27typedef SmallVector<const MemRegion *, 2> RegionVector;
28
29class ValistChecker : public Checker<check::PreCall, check::PreStmt<VAArgExpr>,
30                                     check::DeadSymbols> {
31  mutable std::unique_ptr<BugType> BT_leakedvalist, BT_uninitaccess;
32
33  struct VAListAccepter {
34    CallDescription Func;
35    int VAListPos;
36  };
37  static const SmallVector<VAListAccepter, 15> VAListAccepters;
38  static const CallDescription VaStart, VaEnd, VaCopy;
39
40public:
41  enum CheckKind {
42    CK_Uninitialized,
43    CK_Unterminated,
44    CK_CopyToSelf,
45    CK_NumCheckKinds
46  };
47
48  DefaultBool ChecksEnabled[CK_NumCheckKinds];
49  CheckerNameRef CheckNames[CK_NumCheckKinds];
50
51  void checkPreStmt(const VAArgExpr *VAA, CheckerContext &C) const;
52  void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
53  void checkDeadSymbols(SymbolReaper &SR, CheckerContext &C) const;
54
55private:
56  const MemRegion *getVAListAsRegion(SVal SV, const Expr *VAExpr,
57                                     bool &IsSymbolic, CheckerContext &C) const;
58  const ExplodedNode *getStartCallSite(const ExplodedNode *N,
59                                       const MemRegion *Reg) const;
60
61  void reportUninitializedAccess(const MemRegion *VAList, StringRef Msg,
62                                 CheckerContext &C) const;
63  void reportLeakedVALists(const RegionVector &LeakedVALists, StringRef Msg1,
64                           StringRef Msg2, CheckerContext &C, ExplodedNode *N,
65                           bool ReportUninit = false) const;
66
67  void checkVAListStartCall(const CallEvent &Call, CheckerContext &C,
68                            bool IsCopy) const;
69  void checkVAListEndCall(const CallEvent &Call, CheckerContext &C) const;
70
71  class ValistBugVisitor : public BugReporterVisitor {
72  public:
73    ValistBugVisitor(const MemRegion *Reg, bool IsLeak = false)
74        : Reg(Reg), IsLeak(IsLeak) {}
75    void Profile(llvm::FoldingSetNodeID &ID) const override {
76      static int X = 0;
77      ID.AddPointer(&X);
78      ID.AddPointer(Reg);
79    }
80    PathDiagnosticPieceRef getEndPath(BugReporterContext &BRC,
81                                      const ExplodedNode *EndPathNode,
82                                      PathSensitiveBugReport &BR) override {
83      if (!IsLeak)
84        return nullptr;
85
86      PathDiagnosticLocation L = BR.getLocation();
87      // Do not add the statement itself as a range in case of leak.
88      return std::make_shared<PathDiagnosticEventPiece>(L, BR.getDescription(),
89                                                        false);
90    }
91    PathDiagnosticPieceRef VisitNode(const ExplodedNode *N,
92                                     BugReporterContext &BRC,
93                                     PathSensitiveBugReport &BR) override;
94
95  private:
96    const MemRegion *Reg;
97    bool IsLeak;
98  };
99};
100
101const SmallVector<ValistChecker::VAListAccepter, 15>
102    ValistChecker::VAListAccepters = {
103        {{"vfprintf", 3}, 2},
104        {{"vfscanf", 3}, 2},
105        {{"vprintf", 2}, 1},
106        {{"vscanf", 2}, 1},
107        {{"vsnprintf", 4}, 3},
108        {{"vsprintf", 3}, 2},
109        {{"vsscanf", 3}, 2},
110        {{"vfwprintf", 3}, 2},
111        {{"vfwscanf", 3}, 2},
112        {{"vwprintf", 2}, 1},
113        {{"vwscanf", 2}, 1},
114        {{"vswprintf", 4}, 3},
115        // vswprintf is the wide version of vsnprintf,
116        // vsprintf has no wide version
117        {{"vswscanf", 3}, 2}};
118
119const CallDescription
120    ValistChecker::VaStart("__builtin_va_start", /*Args=*/2, /*Params=*/1),
121    ValistChecker::VaCopy("__builtin_va_copy", 2),
122    ValistChecker::VaEnd("__builtin_va_end", 1);
123} // end anonymous namespace
124
125void ValistChecker::checkPreCall(const CallEvent &Call,
126                                 CheckerContext &C) const {
127  if (!Call.isGlobalCFunction())
128    return;
129  if (Call.isCalled(VaStart))
130    checkVAListStartCall(Call, C, false);
131  else if (Call.isCalled(VaCopy))
132    checkVAListStartCall(Call, C, true);
133  else if (Call.isCalled(VaEnd))
134    checkVAListEndCall(Call, C);
135  else {
136    for (auto FuncInfo : VAListAccepters) {
137      if (!Call.isCalled(FuncInfo.Func))
138        continue;
139      bool Symbolic;
140      const MemRegion *VAList =
141          getVAListAsRegion(Call.getArgSVal(FuncInfo.VAListPos),
142                            Call.getArgExpr(FuncInfo.VAListPos), Symbolic, C);
143      if (!VAList)
144        return;
145
146      if (C.getState()->contains<InitializedVALists>(VAList))
147        return;
148
149      // We did not see va_start call, but the source of the region is unknown.
150      // Be conservative and assume the best.
151      if (Symbolic)
152        return;
153
154      SmallString<80> Errmsg("Function '");
155      Errmsg += FuncInfo.Func.getFunctionName();
156      Errmsg += "' is called with an uninitialized va_list argument";
157      reportUninitializedAccess(VAList, Errmsg.c_str(), C);
158      break;
159    }
160  }
161}
162
163const MemRegion *ValistChecker::getVAListAsRegion(SVal SV, const Expr *E,
164                                                  bool &IsSymbolic,
165                                                  CheckerContext &C) const {
166  const MemRegion *Reg = SV.getAsRegion();
167  if (!Reg)
168    return nullptr;
169  // TODO: In the future this should be abstracted away by the analyzer.
170  bool VaListModelledAsArray = false;
171  if (const auto *Cast = dyn_cast<CastExpr>(E)) {
172    QualType Ty = Cast->getType();
173    VaListModelledAsArray =
174        Ty->isPointerType() && Ty->getPointeeType()->isRecordType();
175  }
176  if (const auto *DeclReg = Reg->getAs<DeclRegion>()) {
177    if (isa<ParmVarDecl>(DeclReg->getDecl()))
178      Reg = C.getState()->getSVal(SV.castAs<Loc>()).getAsRegion();
179  }
180  IsSymbolic = Reg && Reg->getAs<SymbolicRegion>();
181  // Some VarRegion based VA lists reach here as ElementRegions.
182  const auto *EReg = dyn_cast_or_null<ElementRegion>(Reg);
183  return (EReg && VaListModelledAsArray) ? EReg->getSuperRegion() : Reg;
184}
185
186void ValistChecker::checkPreStmt(const VAArgExpr *VAA,
187                                 CheckerContext &C) const {
188  ProgramStateRef State = C.getState();
189  const Expr *VASubExpr = VAA->getSubExpr();
190  SVal VAListSVal = C.getSVal(VASubExpr);
191  bool Symbolic;
192  const MemRegion *VAList =
193      getVAListAsRegion(VAListSVal, VASubExpr, Symbolic, C);
194  if (!VAList)
195    return;
196  if (Symbolic)
197    return;
198  if (!State->contains<InitializedVALists>(VAList))
199    reportUninitializedAccess(
200        VAList, "va_arg() is called on an uninitialized va_list", C);
201}
202
203void ValistChecker::checkDeadSymbols(SymbolReaper &SR,
204                                     CheckerContext &C) const {
205  ProgramStateRef State = C.getState();
206  InitializedVAListsTy TrackedVALists = State->get<InitializedVALists>();
207  RegionVector LeakedVALists;
208  for (auto Reg : TrackedVALists) {
209    if (SR.isLiveRegion(Reg))
210      continue;
211    LeakedVALists.push_back(Reg);
212    State = State->remove<InitializedVALists>(Reg);
213  }
214  if (ExplodedNode *N = C.addTransition(State))
215    reportLeakedVALists(LeakedVALists, "Initialized va_list", " is leaked", C,
216                        N);
217}
218
219// This function traverses the exploded graph backwards and finds the node where
220// the va_list is initialized. That node is used for uniquing the bug paths.
221// It is not likely that there are several different va_lists that belongs to
222// different stack frames, so that case is not yet handled.
223const ExplodedNode *
224ValistChecker::getStartCallSite(const ExplodedNode *N,
225                                const MemRegion *Reg) const {
226  const LocationContext *LeakContext = N->getLocationContext();
227  const ExplodedNode *StartCallNode = N;
228
229  bool FoundInitializedState = false;
230
231  while (N) {
232    ProgramStateRef State = N->getState();
233    if (!State->contains<InitializedVALists>(Reg)) {
234      if (FoundInitializedState)
235        break;
236    } else {
237      FoundInitializedState = true;
238    }
239    const LocationContext *NContext = N->getLocationContext();
240    if (NContext == LeakContext || NContext->isParentOf(LeakContext))
241      StartCallNode = N;
242    N = N->pred_empty() ? nullptr : *(N->pred_begin());
243  }
244
245  return StartCallNode;
246}
247
248void ValistChecker::reportUninitializedAccess(const MemRegion *VAList,
249                                              StringRef Msg,
250                                              CheckerContext &C) const {
251  if (!ChecksEnabled[CK_Uninitialized])
252    return;
253  if (ExplodedNode *N = C.generateErrorNode()) {
254    if (!BT_uninitaccess)
255      BT_uninitaccess.reset(new BugType(CheckNames[CK_Uninitialized],
256                                        "Uninitialized va_list",
257                                        categories::MemoryError));
258    auto R = std::make_unique<PathSensitiveBugReport>(*BT_uninitaccess, Msg, N);
259    R->markInteresting(VAList);
260    R->addVisitor(std::make_unique<ValistBugVisitor>(VAList));
261    C.emitReport(std::move(R));
262  }
263}
264
265void ValistChecker::reportLeakedVALists(const RegionVector &LeakedVALists,
266                                        StringRef Msg1, StringRef Msg2,
267                                        CheckerContext &C, ExplodedNode *N,
268                                        bool ReportUninit) const {
269  if (!(ChecksEnabled[CK_Unterminated] ||
270        (ChecksEnabled[CK_Uninitialized] && ReportUninit)))
271    return;
272  for (auto Reg : LeakedVALists) {
273    if (!BT_leakedvalist) {
274      // FIXME: maybe creating a new check name for this type of bug is a better
275      // solution.
276      BT_leakedvalist.reset(
277          new BugType(CheckNames[CK_Unterminated].getName().empty()
278                          ? CheckNames[CK_Uninitialized]
279                          : CheckNames[CK_Unterminated],
280                      "Leaked va_list", categories::MemoryError,
281                      /*SuppressOnSink=*/true));
282    }
283
284    const ExplodedNode *StartNode = getStartCallSite(N, Reg);
285    PathDiagnosticLocation LocUsedForUniqueing;
286
287    if (const Stmt *StartCallStmt = StartNode->getStmtForDiagnostics())
288      LocUsedForUniqueing = PathDiagnosticLocation::createBegin(
289          StartCallStmt, C.getSourceManager(), StartNode->getLocationContext());
290
291    SmallString<100> Buf;
292    llvm::raw_svector_ostream OS(Buf);
293    OS << Msg1;
294    std::string VariableName = Reg->getDescriptiveName();
295    if (!VariableName.empty())
296      OS << " " << VariableName;
297    OS << Msg2;
298
299    auto R = std::make_unique<PathSensitiveBugReport>(
300        *BT_leakedvalist, OS.str(), N, LocUsedForUniqueing,
301        StartNode->getLocationContext()->getDecl());
302    R->markInteresting(Reg);
303    R->addVisitor(std::make_unique<ValistBugVisitor>(Reg, true));
304    C.emitReport(std::move(R));
305  }
306}
307
308void ValistChecker::checkVAListStartCall(const CallEvent &Call,
309                                         CheckerContext &C, bool IsCopy) const {
310  bool Symbolic;
311  const MemRegion *VAList =
312      getVAListAsRegion(Call.getArgSVal(0), Call.getArgExpr(0), Symbolic, C);
313  if (!VAList)
314    return;
315
316  ProgramStateRef State = C.getState();
317
318  if (IsCopy) {
319    const MemRegion *Arg2 =
320        getVAListAsRegion(Call.getArgSVal(1), Call.getArgExpr(1), Symbolic, C);
321    if (Arg2) {
322      if (ChecksEnabled[CK_CopyToSelf] && VAList == Arg2) {
323        RegionVector LeakedVALists{VAList};
324        if (ExplodedNode *N = C.addTransition(State))
325          reportLeakedVALists(LeakedVALists, "va_list",
326                              " is copied onto itself", C, N, true);
327        return;
328      } else if (!State->contains<InitializedVALists>(Arg2) && !Symbolic) {
329        if (State->contains<InitializedVALists>(VAList)) {
330          State = State->remove<InitializedVALists>(VAList);
331          RegionVector LeakedVALists{VAList};
332          if (ExplodedNode *N = C.addTransition(State))
333            reportLeakedVALists(LeakedVALists, "Initialized va_list",
334                                " is overwritten by an uninitialized one", C, N,
335                                true);
336        } else {
337          reportUninitializedAccess(Arg2, "Uninitialized va_list is copied", C);
338        }
339        return;
340      }
341    }
342  }
343  if (State->contains<InitializedVALists>(VAList)) {
344    RegionVector LeakedVALists{VAList};
345    if (ExplodedNode *N = C.addTransition(State))
346      reportLeakedVALists(LeakedVALists, "Initialized va_list",
347                          " is initialized again", C, N);
348    return;
349  }
350
351  State = State->add<InitializedVALists>(VAList);
352  C.addTransition(State);
353}
354
355void ValistChecker::checkVAListEndCall(const CallEvent &Call,
356                                       CheckerContext &C) const {
357  bool Symbolic;
358  const MemRegion *VAList =
359      getVAListAsRegion(Call.getArgSVal(0), Call.getArgExpr(0), Symbolic, C);
360  if (!VAList)
361    return;
362
363  // We did not see va_start call, but the source of the region is unknown.
364  // Be conservative and assume the best.
365  if (Symbolic)
366    return;
367
368  if (!C.getState()->contains<InitializedVALists>(VAList)) {
369    reportUninitializedAccess(
370        VAList, "va_end() is called on an uninitialized va_list", C);
371    return;
372  }
373  ProgramStateRef State = C.getState();
374  State = State->remove<InitializedVALists>(VAList);
375  C.addTransition(State);
376}
377
378PathDiagnosticPieceRef ValistChecker::ValistBugVisitor::VisitNode(
379    const ExplodedNode *N, BugReporterContext &BRC, PathSensitiveBugReport &) {
380  ProgramStateRef State = N->getState();
381  ProgramStateRef StatePrev = N->getFirstPred()->getState();
382
383  const Stmt *S = N->getStmtForDiagnostics();
384  if (!S)
385    return nullptr;
386
387  StringRef Msg;
388  if (State->contains<InitializedVALists>(Reg) &&
389      !StatePrev->contains<InitializedVALists>(Reg))
390    Msg = "Initialized va_list";
391  else if (!State->contains<InitializedVALists>(Reg) &&
392           StatePrev->contains<InitializedVALists>(Reg))
393    Msg = "Ended va_list";
394
395  if (Msg.empty())
396    return nullptr;
397
398  PathDiagnosticLocation Pos(S, BRC.getSourceManager(),
399                             N->getLocationContext());
400  return std::make_shared<PathDiagnosticEventPiece>(Pos, Msg, true);
401}
402
403void ento::registerValistBase(CheckerManager &mgr) {
404  mgr.registerChecker<ValistChecker>();
405}
406
407bool ento::shouldRegisterValistBase(const CheckerManager &mgr) {
408  return true;
409}
410
411#define REGISTER_CHECKER(name)                                                 \
412  void ento::register##name##Checker(CheckerManager &mgr) {                    \
413    ValistChecker *checker = mgr.getChecker<ValistChecker>();                  \
414    checker->ChecksEnabled[ValistChecker::CK_##name] = true;                   \
415    checker->CheckNames[ValistChecker::CK_##name] =                            \
416        mgr.getCurrentCheckerName();                                           \
417  }                                                                            \
418                                                                               \
419  bool ento::shouldRegister##name##Checker(const CheckerManager &mgr) {            \
420    return true;                                                               \
421  }
422
423REGISTER_CHECKER(Uninitialized)
424REGISTER_CHECKER(Unterminated)
425REGISTER_CHECKER(CopyToSelf)
426