clang/lib/StaticAnalyzer/Checkers/ValistChecker.cpp

   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/CallDescription.h"
  19 #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
  20 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
  21
  22 using namespace clang;
  23 using namespace ento;
  24
  25 REGISTER_SET_WITH_PROGRAMSTATE(InitializedVALists, const MemRegion *)
  26
  27 namespace {
  28 typedef SmallVector<const MemRegion *, 2> RegionVector;
  29
  30 class ValistChecker : public Checker<check::PreCall, check::PreStmt<VAArgExpr>,
  31                                      check::DeadSymbols> {
  32   mutable std::unique_ptr<BugType> BT_leakedvalist, BT_uninitaccess;
  33
  34   struct VAListAccepter {
  35     CallDescription Func;
  36     int VAListPos;
  37   };
  38   static const SmallVector<VAListAccepter, 15> VAListAccepters;
  39   static const CallDescription VaStart, VaEnd, VaCopy;
  40
  41 public:
  42   enum CheckKind {
  43     CK_Uninitialized,
  44     CK_Unterminated,
  45     CK_CopyToSelf,
  46     CK_NumCheckKinds
  47   };
  48
  49   bool ChecksEnabled[CK_NumCheckKinds] = {false};
  50   CheckerNameRef CheckNames[CK_NumCheckKinds];
  51
  52   void checkPreStmt(const VAArgExpr *VAA, CheckerContext &C) const;
  53   void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
  54   void checkDeadSymbols(SymbolReaper &SR, CheckerContext &C) const;
  55
  56 private:
  57   const MemRegion *getVAListAsRegion(SVal SV, const Expr *VAExpr,
  58                                      bool &IsSymbolic, CheckerContext &C) const;
  59   const ExplodedNode *getStartCallSite(const ExplodedNode *N,
  60                                        const MemRegion *Reg) const;
  61
  62   void reportUninitializedAccess(const MemRegion *VAList, StringRef Msg,
  63                                  CheckerContext &C) const;
  64   void reportLeakedVALists(const RegionVector &LeakedVALists, StringRef Msg1,
  65                            StringRef Msg2, CheckerContext &C, ExplodedNode *N,
  66                            bool ReportUninit = false) const;
  67
  68   void checkVAListStartCall(const CallEvent &Call, CheckerContext &C,
  69                             bool IsCopy) const;
  70   void checkVAListEndCall(const CallEvent &Call, CheckerContext &C) const;
  71
  72   class ValistBugVisitor : public BugReporterVisitor {
  73   public:
  74     ValistBugVisitor(const MemRegion *Reg, bool IsLeak = false)
  75         : Reg(Reg), IsLeak(IsLeak) {}
  76     void Profile(llvm::FoldingSetNodeID &ID) const override {
  77       static int X = 0;
  78       ID.AddPointer(&X);
  79       ID.AddPointer(Reg);
  80     }
  81     PathDiagnosticPieceRef getEndPath(BugReporterContext &BRC,
  82                                       const ExplodedNode *EndPathNode,
  83                                       PathSensitiveBugReport &BR) override {
  84       if (!IsLeak)
  85         return nullptr;
  86
  87       PathDiagnosticLocation L = BR.getLocation();
  88       // Do not add the statement itself as a range in case of leak.
  89       return std::make_shared<PathDiagnosticEventPiece>(L, BR.getDescription(),
  90                                                         false);
  91     }
  92     PathDiagnosticPieceRef VisitNode(const ExplodedNode *N,
  93                                      BugReporterContext &BRC,
  94                                      PathSensitiveBugReport &BR) override;
  95
  96   private:
  97     const MemRegion *Reg;
  98     bool IsLeak;
  99   };
 100 };
 101
 102 const SmallVector<ValistChecker::VAListAccepter, 15>
 103     ValistChecker::VAListAccepters = {{{{"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
 116                                       // vsnprintf, vsprintf has no wide version
 117                                       {{{"vswscanf"}, 3}, 2}};
 118
 119 const CallDescription ValistChecker::VaStart({"__builtin_va_start"}, /*Args=*/2,
 120                                              /*Params=*/1),
 121     ValistChecker::VaCopy({"__builtin_va_copy"}, 2),
 122     ValistChecker::VaEnd({"__builtin_va_end"}, 1);
 123 } // end anonymous namespace
 124
 125 void ValistChecker::checkPreCall(const CallEvent &Call,
 126                                  CheckerContext &C) const {
 127   if (!Call.isGlobalCFunction())
 128     return;
 129   if (VaStart.matches(Call))
 130     checkVAListStartCall(Call, C, false);
 131   else if (VaCopy.matches(Call))
 132     checkVAListStartCall(Call, C, true);
 133   else if (VaEnd.matches(Call))
 134     checkVAListEndCall(Call, C);
 135   else {
 136     for (auto FuncInfo : VAListAccepters) {
 137       if (!FuncInfo.Func.matches(Call))
 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
 163 const 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->getBaseRegion()->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
 186 void 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
 203 void 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.
 223 const ExplodedNode *
 224 ValistChecker::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
 248 void 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
 265 void 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
 308 void 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
 355 void 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
 378 PathDiagnosticPieceRef 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
 403 void ento::registerValistBase(CheckerManager &mgr) {
 404   mgr.registerChecker<ValistChecker>();
 405 }
 406
 407 bool 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
 423 REGISTER_CHECKER(Uninitialized)
 424 REGISTER_CHECKER(Unterminated)
 425 REGISTER_CHECKER(CopyToSelf)