1 //= UnixAPIChecker.h - Checks preconditions for various Unix APIs --*- 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 UnixAPIChecker, which is an assortment of checks on calls 10 // to various, widely used UNIX/Posix functions. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "clang/Basic/TargetInfo.h" 15 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h" 16 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h" 17 #include "clang/StaticAnalyzer/Core/BugReporter/CommonBugCategories.h" 18 #include "clang/StaticAnalyzer/Core/Checker.h" 19 #include "clang/StaticAnalyzer/Core/CheckerManager.h" 20 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h" 21 #include "llvm/ADT/STLExtras.h" 22 #include "llvm/ADT/SmallString.h" 23 #include "llvm/ADT/StringExtras.h" 24 #include "llvm/Support/raw_ostream.h" 25 #include <optional> 26 27 using namespace clang; 28 using namespace ento; 29 30 enum class OpenVariant { 31 /// The standard open() call: 32 /// int open(const char *path, int oflag, ...); 33 Open, 34 35 /// The variant taking a directory file descriptor and a relative path: 36 /// int openat(int fd, const char *path, int oflag, ...); 37 OpenAt 38 }; 39 40 namespace { 41 42 class UnixAPIMisuseChecker : public Checker< check::PreStmt<CallExpr> > { 43 const BugType BT_open{this, "Improper use of 'open'", categories::UnixAPI}; 44 const BugType BT_pthreadOnce{this, "Improper use of 'pthread_once'", 45 categories::UnixAPI}; 46 mutable std::optional<uint64_t> Val_O_CREAT; 47 48 public: 49 void checkPreStmt(const CallExpr *CE, CheckerContext &C) const; 50 51 void CheckOpen(CheckerContext &C, const CallExpr *CE) const; 52 void CheckOpenAt(CheckerContext &C, const CallExpr *CE) const; 53 void CheckPthreadOnce(CheckerContext &C, const CallExpr *CE) const; 54 55 void CheckOpenVariant(CheckerContext &C, 56 const CallExpr *CE, OpenVariant Variant) const; 57 58 void ReportOpenBug(CheckerContext &C, 59 ProgramStateRef State, 60 const char *Msg, 61 SourceRange SR) const; 62 63 }; 64 65 class UnixAPIPortabilityChecker : public Checker< check::PreStmt<CallExpr> > { 66 public: 67 void checkPreStmt(const CallExpr *CE, CheckerContext &C) const; 68 69 private: 70 const BugType BT_mallocZero{ 71 this, "Undefined allocation of 0 bytes (CERT MEM04-C; CWE-131)", 72 categories::UnixAPI}; 73 74 void CheckCallocZero(CheckerContext &C, const CallExpr *CE) const; 75 void CheckMallocZero(CheckerContext &C, const CallExpr *CE) const; 76 void CheckReallocZero(CheckerContext &C, const CallExpr *CE) const; 77 void CheckReallocfZero(CheckerContext &C, const CallExpr *CE) const; 78 void CheckAllocaZero(CheckerContext &C, const CallExpr *CE) const; 79 void CheckAllocaWithAlignZero(CheckerContext &C, const CallExpr *CE) const; 80 void CheckVallocZero(CheckerContext &C, const CallExpr *CE) const; 81 82 bool ReportZeroByteAllocation(CheckerContext &C, 83 ProgramStateRef falseState, 84 const Expr *arg, 85 const char *fn_name) const; 86 void BasicAllocationCheck(CheckerContext &C, 87 const CallExpr *CE, 88 const unsigned numArgs, 89 const unsigned sizeArg, 90 const char *fn) const; 91 }; 92 93 } //end anonymous namespace 94 95 //===----------------------------------------------------------------------===// 96 // "open" (man 2 open) 97 //===----------------------------------------------------------------------===/ 98 99 void UnixAPIMisuseChecker::checkPreStmt(const CallExpr *CE, 100 CheckerContext &C) const { 101 const FunctionDecl *FD = C.getCalleeDecl(CE); 102 if (!FD || FD->getKind() != Decl::Function) 103 return; 104 105 // Don't treat functions in namespaces with the same name a Unix function 106 // as a call to the Unix function. 107 const DeclContext *NamespaceCtx = FD->getEnclosingNamespaceContext(); 108 if (isa_and_nonnull<NamespaceDecl>(NamespaceCtx)) 109 return; 110 111 StringRef FName = C.getCalleeName(FD); 112 if (FName.empty()) 113 return; 114 115 if (FName == "open") 116 CheckOpen(C, CE); 117 118 else if (FName == "openat") 119 CheckOpenAt(C, CE); 120 121 else if (FName == "pthread_once") 122 CheckPthreadOnce(C, CE); 123 } 124 void UnixAPIMisuseChecker::ReportOpenBug(CheckerContext &C, 125 ProgramStateRef State, 126 const char *Msg, 127 SourceRange SR) const { 128 ExplodedNode *N = C.generateErrorNode(State); 129 if (!N) 130 return; 131 132 auto Report = std::make_unique<PathSensitiveBugReport>(BT_open, Msg, N); 133 Report->addRange(SR); 134 C.emitReport(std::move(Report)); 135 } 136 137 void UnixAPIMisuseChecker::CheckOpen(CheckerContext &C, 138 const CallExpr *CE) const { 139 CheckOpenVariant(C, CE, OpenVariant::Open); 140 } 141 142 void UnixAPIMisuseChecker::CheckOpenAt(CheckerContext &C, 143 const CallExpr *CE) const { 144 CheckOpenVariant(C, CE, OpenVariant::OpenAt); 145 } 146 147 void UnixAPIMisuseChecker::CheckOpenVariant(CheckerContext &C, 148 const CallExpr *CE, 149 OpenVariant Variant) const { 150 // The index of the argument taking the flags open flags (O_RDONLY, 151 // O_WRONLY, O_CREAT, etc.), 152 unsigned int FlagsArgIndex; 153 const char *VariantName; 154 switch (Variant) { 155 case OpenVariant::Open: 156 FlagsArgIndex = 1; 157 VariantName = "open"; 158 break; 159 case OpenVariant::OpenAt: 160 FlagsArgIndex = 2; 161 VariantName = "openat"; 162 break; 163 }; 164 165 // All calls should at least provide arguments up to the 'flags' parameter. 166 unsigned int MinArgCount = FlagsArgIndex + 1; 167 168 // If the flags has O_CREAT set then open/openat() require an additional 169 // argument specifying the file mode (permission bits) for the created file. 170 unsigned int CreateModeArgIndex = FlagsArgIndex + 1; 171 172 // The create mode argument should be the last argument. 173 unsigned int MaxArgCount = CreateModeArgIndex + 1; 174 175 ProgramStateRef state = C.getState(); 176 177 if (CE->getNumArgs() < MinArgCount) { 178 // The frontend should issue a warning for this case. Just return. 179 return; 180 } else if (CE->getNumArgs() == MaxArgCount) { 181 const Expr *Arg = CE->getArg(CreateModeArgIndex); 182 QualType QT = Arg->getType(); 183 if (!QT->isIntegerType()) { 184 SmallString<256> SBuf; 185 llvm::raw_svector_ostream OS(SBuf); 186 OS << "The " << CreateModeArgIndex + 1 187 << llvm::getOrdinalSuffix(CreateModeArgIndex + 1) 188 << " argument to '" << VariantName << "' is not an integer"; 189 190 ReportOpenBug(C, state, 191 SBuf.c_str(), 192 Arg->getSourceRange()); 193 return; 194 } 195 } else if (CE->getNumArgs() > MaxArgCount) { 196 SmallString<256> SBuf; 197 llvm::raw_svector_ostream OS(SBuf); 198 OS << "Call to '" << VariantName << "' with more than " << MaxArgCount 199 << " arguments"; 200 201 ReportOpenBug(C, state, 202 SBuf.c_str(), 203 CE->getArg(MaxArgCount)->getSourceRange()); 204 return; 205 } 206 207 // The definition of O_CREAT is platform specific. We need a better way 208 // of querying this information from the checking environment. 209 if (!Val_O_CREAT) { 210 if (C.getASTContext().getTargetInfo().getTriple().getVendor() 211 == llvm::Triple::Apple) 212 Val_O_CREAT = 0x0200; 213 else { 214 // FIXME: We need a more general way of getting the O_CREAT value. 215 // We could possibly grovel through the preprocessor state, but 216 // that would require passing the Preprocessor object to the ExprEngine. 217 // See also: MallocChecker.cpp / M_ZERO. 218 return; 219 } 220 } 221 222 // Now check if oflags has O_CREAT set. 223 const Expr *oflagsEx = CE->getArg(FlagsArgIndex); 224 const SVal V = C.getSVal(oflagsEx); 225 if (!isa<NonLoc>(V)) { 226 // The case where 'V' can be a location can only be due to a bad header, 227 // so in this case bail out. 228 return; 229 } 230 NonLoc oflags = V.castAs<NonLoc>(); 231 NonLoc ocreateFlag = C.getSValBuilder() 232 .makeIntVal(*Val_O_CREAT, oflagsEx->getType()) 233 .castAs<NonLoc>(); 234 SVal maskedFlagsUC = C.getSValBuilder().evalBinOpNN(state, BO_And, 235 oflags, ocreateFlag, 236 oflagsEx->getType()); 237 if (maskedFlagsUC.isUnknownOrUndef()) 238 return; 239 DefinedSVal maskedFlags = maskedFlagsUC.castAs<DefinedSVal>(); 240 241 // Check if maskedFlags is non-zero. 242 ProgramStateRef trueState, falseState; 243 std::tie(trueState, falseState) = state->assume(maskedFlags); 244 245 // Only emit an error if the value of 'maskedFlags' is properly 246 // constrained; 247 if (!(trueState && !falseState)) 248 return; 249 250 if (CE->getNumArgs() < MaxArgCount) { 251 SmallString<256> SBuf; 252 llvm::raw_svector_ostream OS(SBuf); 253 OS << "Call to '" << VariantName << "' requires a " 254 << CreateModeArgIndex + 1 255 << llvm::getOrdinalSuffix(CreateModeArgIndex + 1) 256 << " argument when the 'O_CREAT' flag is set"; 257 ReportOpenBug(C, trueState, 258 SBuf.c_str(), 259 oflagsEx->getSourceRange()); 260 } 261 } 262 263 //===----------------------------------------------------------------------===// 264 // pthread_once 265 //===----------------------------------------------------------------------===// 266 267 void UnixAPIMisuseChecker::CheckPthreadOnce(CheckerContext &C, 268 const CallExpr *CE) const { 269 270 // This is similar to 'CheckDispatchOnce' in the MacOSXAPIChecker. 271 // They can possibly be refactored. 272 273 if (CE->getNumArgs() < 1) 274 return; 275 276 // Check if the first argument is stack allocated. If so, issue a warning 277 // because that's likely to be bad news. 278 ProgramStateRef state = C.getState(); 279 const MemRegion *R = C.getSVal(CE->getArg(0)).getAsRegion(); 280 if (!R || !isa<StackSpaceRegion>(R->getMemorySpace())) 281 return; 282 283 ExplodedNode *N = C.generateErrorNode(state); 284 if (!N) 285 return; 286 287 SmallString<256> S; 288 llvm::raw_svector_ostream os(S); 289 os << "Call to 'pthread_once' uses"; 290 if (const VarRegion *VR = dyn_cast<VarRegion>(R)) 291 os << " the local variable '" << VR->getDecl()->getName() << '\''; 292 else 293 os << " stack allocated memory"; 294 os << " for the \"control\" value. Using such transient memory for " 295 "the control value is potentially dangerous."; 296 if (isa<VarRegion>(R) && isa<StackLocalsSpaceRegion>(R->getMemorySpace())) 297 os << " Perhaps you intended to declare the variable as 'static'?"; 298 299 auto report = 300 std::make_unique<PathSensitiveBugReport>(BT_pthreadOnce, os.str(), N); 301 report->addRange(CE->getArg(0)->getSourceRange()); 302 C.emitReport(std::move(report)); 303 } 304 305 //===----------------------------------------------------------------------===// 306 // "calloc", "malloc", "realloc", "reallocf", "alloca" and "valloc" 307 // with allocation size 0 308 //===----------------------------------------------------------------------===// 309 310 // FIXME: Eventually these should be rolled into the MallocChecker, but right now 311 // they're more basic and valuable for widespread use. 312 313 // Returns true if we try to do a zero byte allocation, false otherwise. 314 // Fills in trueState and falseState. 315 static bool IsZeroByteAllocation(ProgramStateRef state, 316 const SVal argVal, 317 ProgramStateRef *trueState, 318 ProgramStateRef *falseState) { 319 std::tie(*trueState, *falseState) = 320 state->assume(argVal.castAs<DefinedSVal>()); 321 322 return (*falseState && !*trueState); 323 } 324 325 // Generates an error report, indicating that the function whose name is given 326 // will perform a zero byte allocation. 327 // Returns false if an error occurred, true otherwise. 328 bool UnixAPIPortabilityChecker::ReportZeroByteAllocation( 329 CheckerContext &C, 330 ProgramStateRef falseState, 331 const Expr *arg, 332 const char *fn_name) const { 333 ExplodedNode *N = C.generateErrorNode(falseState); 334 if (!N) 335 return false; 336 337 SmallString<256> S; 338 llvm::raw_svector_ostream os(S); 339 os << "Call to '" << fn_name << "' has an allocation size of 0 bytes"; 340 auto report = 341 std::make_unique<PathSensitiveBugReport>(BT_mallocZero, os.str(), N); 342 343 report->addRange(arg->getSourceRange()); 344 bugreporter::trackExpressionValue(N, arg, *report); 345 C.emitReport(std::move(report)); 346 347 return true; 348 } 349 350 // Does a basic check for 0-sized allocations suitable for most of the below 351 // functions (modulo "calloc") 352 void UnixAPIPortabilityChecker::BasicAllocationCheck(CheckerContext &C, 353 const CallExpr *CE, 354 const unsigned numArgs, 355 const unsigned sizeArg, 356 const char *fn) const { 357 // Check for the correct number of arguments. 358 if (CE->getNumArgs() != numArgs) 359 return; 360 361 // Check if the allocation size is 0. 362 ProgramStateRef state = C.getState(); 363 ProgramStateRef trueState = nullptr, falseState = nullptr; 364 const Expr *arg = CE->getArg(sizeArg); 365 SVal argVal = C.getSVal(arg); 366 367 if (argVal.isUnknownOrUndef()) 368 return; 369 370 // Is the value perfectly constrained to zero? 371 if (IsZeroByteAllocation(state, argVal, &trueState, &falseState)) { 372 (void) ReportZeroByteAllocation(C, falseState, arg, fn); 373 return; 374 } 375 // Assume the value is non-zero going forward. 376 assert(trueState); 377 if (trueState != state) 378 C.addTransition(trueState); 379 } 380 381 void UnixAPIPortabilityChecker::CheckCallocZero(CheckerContext &C, 382 const CallExpr *CE) const { 383 unsigned int nArgs = CE->getNumArgs(); 384 if (nArgs != 2) 385 return; 386 387 ProgramStateRef state = C.getState(); 388 ProgramStateRef trueState = nullptr, falseState = nullptr; 389 390 unsigned int i; 391 for (i = 0; i < nArgs; i++) { 392 const Expr *arg = CE->getArg(i); 393 SVal argVal = C.getSVal(arg); 394 if (argVal.isUnknownOrUndef()) { 395 if (i == 0) 396 continue; 397 else 398 return; 399 } 400 401 if (IsZeroByteAllocation(state, argVal, &trueState, &falseState)) { 402 if (ReportZeroByteAllocation(C, falseState, arg, "calloc")) 403 return; 404 else if (i == 0) 405 continue; 406 else 407 return; 408 } 409 } 410 411 // Assume the value is non-zero going forward. 412 assert(trueState); 413 if (trueState != state) 414 C.addTransition(trueState); 415 } 416 417 void UnixAPIPortabilityChecker::CheckMallocZero(CheckerContext &C, 418 const CallExpr *CE) const { 419 BasicAllocationCheck(C, CE, 1, 0, "malloc"); 420 } 421 422 void UnixAPIPortabilityChecker::CheckReallocZero(CheckerContext &C, 423 const CallExpr *CE) const { 424 BasicAllocationCheck(C, CE, 2, 1, "realloc"); 425 } 426 427 void UnixAPIPortabilityChecker::CheckReallocfZero(CheckerContext &C, 428 const CallExpr *CE) const { 429 BasicAllocationCheck(C, CE, 2, 1, "reallocf"); 430 } 431 432 void UnixAPIPortabilityChecker::CheckAllocaZero(CheckerContext &C, 433 const CallExpr *CE) const { 434 BasicAllocationCheck(C, CE, 1, 0, "alloca"); 435 } 436 437 void UnixAPIPortabilityChecker::CheckAllocaWithAlignZero( 438 CheckerContext &C, 439 const CallExpr *CE) const { 440 BasicAllocationCheck(C, CE, 2, 0, "__builtin_alloca_with_align"); 441 } 442 443 void UnixAPIPortabilityChecker::CheckVallocZero(CheckerContext &C, 444 const CallExpr *CE) const { 445 BasicAllocationCheck(C, CE, 1, 0, "valloc"); 446 } 447 448 void UnixAPIPortabilityChecker::checkPreStmt(const CallExpr *CE, 449 CheckerContext &C) const { 450 const FunctionDecl *FD = C.getCalleeDecl(CE); 451 if (!FD || FD->getKind() != Decl::Function) 452 return; 453 454 // Don't treat functions in namespaces with the same name a Unix function 455 // as a call to the Unix function. 456 const DeclContext *NamespaceCtx = FD->getEnclosingNamespaceContext(); 457 if (isa_and_nonnull<NamespaceDecl>(NamespaceCtx)) 458 return; 459 460 StringRef FName = C.getCalleeName(FD); 461 if (FName.empty()) 462 return; 463 464 if (FName == "calloc") 465 CheckCallocZero(C, CE); 466 467 else if (FName == "malloc") 468 CheckMallocZero(C, CE); 469 470 else if (FName == "realloc") 471 CheckReallocZero(C, CE); 472 473 else if (FName == "reallocf") 474 CheckReallocfZero(C, CE); 475 476 else if (FName == "alloca" || FName == "__builtin_alloca") 477 CheckAllocaZero(C, CE); 478 479 else if (FName == "__builtin_alloca_with_align") 480 CheckAllocaWithAlignZero(C, CE); 481 482 else if (FName == "valloc") 483 CheckVallocZero(C, CE); 484 } 485 486 //===----------------------------------------------------------------------===// 487 // Registration. 488 //===----------------------------------------------------------------------===// 489 490 #define REGISTER_CHECKER(CHECKERNAME) \ 491 void ento::register##CHECKERNAME(CheckerManager &mgr) { \ 492 mgr.registerChecker<CHECKERNAME>(); \ 493 } \ 494 \ 495 bool ento::shouldRegister##CHECKERNAME(const CheckerManager &mgr) { \ 496 return true; \ 497 } 498 499 REGISTER_CHECKER(UnixAPIMisuseChecker) 500 REGISTER_CHECKER(UnixAPIPortabilityChecker) 501