CheckSecuritySyntaxOnly.cpp revision e0e29332c89da22b6890929b97e6f568c917d85f
1//==- CheckSecuritySyntaxOnly.cpp - Basic security checks --------*- 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// This file defines a set of flow-insensitive security checks. 11// 12//===----------------------------------------------------------------------===// 13 14#include "ClangSACheckers.h" 15#include "clang/StaticAnalyzer/Core/Checker.h" 16#include "clang/StaticAnalyzer/Core/BugReporter/BugReporter.h" 17#include "clang/Basic/TargetInfo.h" 18#include "clang/AST/StmtVisitor.h" 19#include "llvm/Support/raw_ostream.h" 20#include "llvm/ADT/StringSwitch.h" 21 22using namespace clang; 23using namespace ento; 24 25static bool isArc4RandomAvailable(const ASTContext &Ctx) { 26 const llvm::Triple &T = Ctx.Target.getTriple(); 27 return T.getVendor() == llvm::Triple::Apple || 28 T.getOS() == llvm::Triple::FreeBSD || 29 T.getOS() == llvm::Triple::NetBSD || 30 T.getOS() == llvm::Triple::OpenBSD || 31 T.getOS() == llvm::Triple::DragonFly; 32} 33 34namespace { 35class WalkAST : public StmtVisitor<WalkAST> { 36 BugReporter &BR; 37 enum { num_setids = 6 }; 38 IdentifierInfo *II_setid[num_setids]; 39 40 const bool CheckRand; 41 42public: 43 WalkAST(BugReporter &br) : BR(br), II_setid(), 44 CheckRand(isArc4RandomAvailable(BR.getContext())) {} 45 46 // Statement visitor methods. 47 void VisitCallExpr(CallExpr *CE); 48 void VisitForStmt(ForStmt *S); 49 void VisitCompoundStmt (CompoundStmt *S); 50 void VisitStmt(Stmt *S) { VisitChildren(S); } 51 52 void VisitChildren(Stmt *S); 53 54 // Helpers. 55 bool checkCall_strCommon(const CallExpr *CE, const FunctionDecl *FD); 56 57 typedef void (WalkAST::*FnCheck)(const CallExpr *, 58 const FunctionDecl *); 59 60 // Checker-specific methods. 61 void checkLoopConditionForFloat(const ForStmt *FS); 62 void checkCall_gets(const CallExpr *CE, const FunctionDecl *FD); 63 void checkCall_getpw(const CallExpr *CE, const FunctionDecl *FD); 64 void checkCall_mktemp(const CallExpr *CE, const FunctionDecl *FD); 65 void checkCall_strcpy(const CallExpr *CE, const FunctionDecl *FD); 66 void checkCall_strcat(const CallExpr *CE, const FunctionDecl *FD); 67 void checkCall_rand(const CallExpr *CE, const FunctionDecl *FD); 68 void checkCall_random(const CallExpr *CE, const FunctionDecl *FD); 69 void checkUncheckedReturnValue(CallExpr *CE); 70}; 71} // end anonymous namespace 72 73//===----------------------------------------------------------------------===// 74// AST walking. 75//===----------------------------------------------------------------------===// 76 77void WalkAST::VisitChildren(Stmt *S) { 78 for (Stmt::child_iterator I = S->child_begin(), E = S->child_end(); I!=E; ++I) 79 if (Stmt *child = *I) 80 Visit(child); 81} 82 83void WalkAST::VisitCallExpr(CallExpr *CE) { 84 // Get the callee. 85 const FunctionDecl *FD = CE->getDirectCallee(); 86 87 if (!FD) 88 return; 89 90 // Get the name of the callee. If it's a builtin, strip off the prefix. 91 IdentifierInfo *II = FD->getIdentifier(); 92 if (!II) // if no identifier, not a simple C function 93 return; 94 StringRef Name = II->getName(); 95 if (Name.startswith("__builtin_")) 96 Name = Name.substr(10); 97 98 // Set the evaluation function by switching on the callee name. 99 FnCheck evalFunction = llvm::StringSwitch<FnCheck>(Name) 100 .Case("gets", &WalkAST::checkCall_gets) 101 .Case("getpw", &WalkAST::checkCall_getpw) 102 .Case("mktemp", &WalkAST::checkCall_mktemp) 103 .Cases("strcpy", "__strcpy_chk", &WalkAST::checkCall_strcpy) 104 .Cases("strcat", "__strcat_chk", &WalkAST::checkCall_strcat) 105 .Case("drand48", &WalkAST::checkCall_rand) 106 .Case("erand48", &WalkAST::checkCall_rand) 107 .Case("jrand48", &WalkAST::checkCall_rand) 108 .Case("lrand48", &WalkAST::checkCall_rand) 109 .Case("mrand48", &WalkAST::checkCall_rand) 110 .Case("nrand48", &WalkAST::checkCall_rand) 111 .Case("lcong48", &WalkAST::checkCall_rand) 112 .Case("rand", &WalkAST::checkCall_rand) 113 .Case("rand_r", &WalkAST::checkCall_rand) 114 .Case("random", &WalkAST::checkCall_random) 115 .Default(NULL); 116 117 // If the callee isn't defined, it is not of security concern. 118 // Check and evaluate the call. 119 if (evalFunction) 120 (this->*evalFunction)(CE, FD); 121 122 // Recurse and check children. 123 VisitChildren(CE); 124} 125 126void WalkAST::VisitCompoundStmt(CompoundStmt *S) { 127 for (Stmt::child_iterator I = S->child_begin(), E = S->child_end(); I!=E; ++I) 128 if (Stmt *child = *I) { 129 if (CallExpr *CE = dyn_cast<CallExpr>(child)) 130 checkUncheckedReturnValue(CE); 131 Visit(child); 132 } 133} 134 135void WalkAST::VisitForStmt(ForStmt *FS) { 136 checkLoopConditionForFloat(FS); 137 138 // Recurse and check children. 139 VisitChildren(FS); 140} 141 142//===----------------------------------------------------------------------===// 143// Check: floating poing variable used as loop counter. 144// Originally: <rdar://problem/6336718> 145// Implements: CERT security coding advisory FLP-30. 146//===----------------------------------------------------------------------===// 147 148static const DeclRefExpr* 149getIncrementedVar(const Expr *expr, const VarDecl *x, const VarDecl *y) { 150 expr = expr->IgnoreParenCasts(); 151 152 if (const BinaryOperator *B = dyn_cast<BinaryOperator>(expr)) { 153 if (!(B->isAssignmentOp() || B->isCompoundAssignmentOp() || 154 B->getOpcode() == BO_Comma)) 155 return NULL; 156 157 if (const DeclRefExpr *lhs = getIncrementedVar(B->getLHS(), x, y)) 158 return lhs; 159 160 if (const DeclRefExpr *rhs = getIncrementedVar(B->getRHS(), x, y)) 161 return rhs; 162 163 return NULL; 164 } 165 166 if (const DeclRefExpr *DR = dyn_cast<DeclRefExpr>(expr)) { 167 const NamedDecl *ND = DR->getDecl(); 168 return ND == x || ND == y ? DR : NULL; 169 } 170 171 if (const UnaryOperator *U = dyn_cast<UnaryOperator>(expr)) 172 return U->isIncrementDecrementOp() 173 ? getIncrementedVar(U->getSubExpr(), x, y) : NULL; 174 175 return NULL; 176} 177 178/// CheckLoopConditionForFloat - This check looks for 'for' statements that 179/// use a floating point variable as a loop counter. 180/// CERT: FLP30-C, FLP30-CPP. 181/// 182void WalkAST::checkLoopConditionForFloat(const ForStmt *FS) { 183 // Does the loop have a condition? 184 const Expr *condition = FS->getCond(); 185 186 if (!condition) 187 return; 188 189 // Does the loop have an increment? 190 const Expr *increment = FS->getInc(); 191 192 if (!increment) 193 return; 194 195 // Strip away '()' and casts. 196 condition = condition->IgnoreParenCasts(); 197 increment = increment->IgnoreParenCasts(); 198 199 // Is the loop condition a comparison? 200 const BinaryOperator *B = dyn_cast<BinaryOperator>(condition); 201 202 if (!B) 203 return; 204 205 // Is this a comparison? 206 if (!(B->isRelationalOp() || B->isEqualityOp())) 207 return; 208 209 // Are we comparing variables? 210 const DeclRefExpr *drLHS = 211 dyn_cast<DeclRefExpr>(B->getLHS()->IgnoreParenLValueCasts()); 212 const DeclRefExpr *drRHS = 213 dyn_cast<DeclRefExpr>(B->getRHS()->IgnoreParenLValueCasts()); 214 215 // Does at least one of the variables have a floating point type? 216 drLHS = drLHS && drLHS->getType()->isRealFloatingType() ? drLHS : NULL; 217 drRHS = drRHS && drRHS->getType()->isRealFloatingType() ? drRHS : NULL; 218 219 if (!drLHS && !drRHS) 220 return; 221 222 const VarDecl *vdLHS = drLHS ? dyn_cast<VarDecl>(drLHS->getDecl()) : NULL; 223 const VarDecl *vdRHS = drRHS ? dyn_cast<VarDecl>(drRHS->getDecl()) : NULL; 224 225 if (!vdLHS && !vdRHS) 226 return; 227 228 // Does either variable appear in increment? 229 const DeclRefExpr *drInc = getIncrementedVar(increment, vdLHS, vdRHS); 230 231 if (!drInc) 232 return; 233 234 // Emit the error. First figure out which DeclRefExpr in the condition 235 // referenced the compared variable. 236 const DeclRefExpr *drCond = vdLHS == drInc->getDecl() ? drLHS : drRHS; 237 238 SmallVector<SourceRange, 2> ranges; 239 llvm::SmallString<256> sbuf; 240 llvm::raw_svector_ostream os(sbuf); 241 242 os << "Variable '" << drCond->getDecl()->getName() 243 << "' with floating point type '" << drCond->getType().getAsString() 244 << "' should not be used as a loop counter"; 245 246 ranges.push_back(drCond->getSourceRange()); 247 ranges.push_back(drInc->getSourceRange()); 248 249 const char *bugType = "Floating point variable used as loop counter"; 250 BR.EmitBasicReport(bugType, "Security", os.str(), 251 FS->getLocStart(), ranges.data(), ranges.size()); 252} 253 254//===----------------------------------------------------------------------===// 255// Check: Any use of 'gets' is insecure. 256// Originally: <rdar://problem/6335715> 257// Implements (part of): 300-BSI (buildsecurityin.us-cert.gov) 258// CWE-242: Use of Inherently Dangerous Function 259//===----------------------------------------------------------------------===// 260 261void WalkAST::checkCall_gets(const CallExpr *CE, const FunctionDecl *FD) { 262 const FunctionProtoType *FPT 263 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens()); 264 if (!FPT) 265 return; 266 267 // Verify that the function takes a single argument. 268 if (FPT->getNumArgs() != 1) 269 return; 270 271 // Is the argument a 'char*'? 272 const PointerType *PT = dyn_cast<PointerType>(FPT->getArgType(0)); 273 if (!PT) 274 return; 275 276 if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy) 277 return; 278 279 // Issue a warning. 280 SourceRange R = CE->getCallee()->getSourceRange(); 281 BR.EmitBasicReport("Potential buffer overflow in call to 'gets'", 282 "Security", 283 "Call to function 'gets' is extremely insecure as it can " 284 "always result in a buffer overflow", 285 CE->getLocStart(), &R, 1); 286} 287 288//===----------------------------------------------------------------------===// 289// Check: Any use of 'getpwd' is insecure. 290// CWE-477: Use of Obsolete Functions 291//===----------------------------------------------------------------------===// 292 293void WalkAST::checkCall_getpw(const CallExpr *CE, const FunctionDecl *FD) { 294 const FunctionProtoType *FPT 295 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens()); 296 if (!FPT) 297 return; 298 299 // Verify that the function takes two arguments. 300 if (FPT->getNumArgs() != 2) 301 return; 302 303 // Verify the first argument type is integer. 304 if (!FPT->getArgType(0)->isIntegerType()) 305 return; 306 307 // Verify the second argument type is char*. 308 const PointerType *PT = dyn_cast<PointerType>(FPT->getArgType(1)); 309 if (!PT) 310 return; 311 312 if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy) 313 return; 314 315 // Issue a warning. 316 SourceRange R = CE->getCallee()->getSourceRange(); 317 BR.EmitBasicReport("Potential buffer overflow in call to 'getpw'", 318 "Security", 319 "The getpw() function is dangerous as it may overflow the " 320 "provided buffer. It is obsoleted by getpwuid().", 321 CE->getLocStart(), &R, 1); 322} 323 324//===----------------------------------------------------------------------===// 325// Check: Any use of 'mktemp' is insecure.It is obsoleted by mkstemp(). 326// CWE-377: Insecure Temporary File 327//===----------------------------------------------------------------------===// 328 329void WalkAST::checkCall_mktemp(const CallExpr *CE, const FunctionDecl *FD) { 330 const FunctionProtoType *FPT 331 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens()); 332 if(!FPT) 333 return; 334 335 // Verify that the function takes a single argument. 336 if (FPT->getNumArgs() != 1) 337 return; 338 339 // Verify that the argument is Pointer Type. 340 const PointerType *PT = dyn_cast<PointerType>(FPT->getArgType(0)); 341 if (!PT) 342 return; 343 344 // Verify that the argument is a 'char*'. 345 if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy) 346 return; 347 348 // Issue a waring. 349 SourceRange R = CE->getCallee()->getSourceRange(); 350 BR.EmitBasicReport("Potential insecure temporary file in call 'mktemp'", 351 "Security", 352 "Call to function 'mktemp' is insecure as it always " 353 "creates or uses insecure temporary file. Use 'mkstemp' instead", 354 CE->getLocStart(), &R, 1); 355} 356 357//===----------------------------------------------------------------------===// 358// Check: Any use of 'strcpy' is insecure. 359// 360// CWE-119: Improper Restriction of Operations within 361// the Bounds of a Memory Buffer 362//===----------------------------------------------------------------------===// 363void WalkAST::checkCall_strcpy(const CallExpr *CE, const FunctionDecl *FD) { 364 if (!checkCall_strCommon(CE, FD)) 365 return; 366 367 // Issue a warning. 368 SourceRange R = CE->getCallee()->getSourceRange(); 369 BR.EmitBasicReport("Potential insecure memory buffer bounds restriction in " 370 "call 'strcpy'", 371 "Security", 372 "Call to function 'strcpy' is insecure as it does not " 373 "provide bounding of the memory buffer. Replace " 374 "unbounded copy functions with analogous functions that " 375 "support length arguments such as 'strncpy'. CWE-119.", 376 CE->getLocStart(), &R, 1); 377} 378 379//===----------------------------------------------------------------------===// 380// Check: Any use of 'strcat' is insecure. 381// 382// CWE-119: Improper Restriction of Operations within 383// the Bounds of a Memory Buffer 384//===----------------------------------------------------------------------===// 385void WalkAST::checkCall_strcat(const CallExpr *CE, const FunctionDecl *FD) { 386 if (!checkCall_strCommon(CE, FD)) 387 return; 388 389 // Issue a warning. 390 SourceRange R = CE->getCallee()->getSourceRange(); 391 BR.EmitBasicReport("Potential insecure memory buffer bounds restriction in " 392 "call 'strcat'", 393 "Security", 394 "Call to function 'strcat' is insecure as it does not " 395 "provide bounding of the memory buffer. Replace " 396 "unbounded copy functions with analogous functions that " 397 "support length arguments such as 'strncat'. CWE-119.", 398 CE->getLocStart(), &R, 1); 399} 400 401//===----------------------------------------------------------------------===// 402// Common check for str* functions with no bounds parameters. 403//===----------------------------------------------------------------------===// 404bool WalkAST::checkCall_strCommon(const CallExpr *CE, const FunctionDecl *FD) { 405 const FunctionProtoType *FPT 406 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens()); 407 if (!FPT) 408 return false; 409 410 // Verify the function takes two arguments, three in the _chk version. 411 int numArgs = FPT->getNumArgs(); 412 if (numArgs != 2 && numArgs != 3) 413 return false; 414 415 // Verify the type for both arguments. 416 for (int i = 0; i < 2; i++) { 417 // Verify that the arguments are pointers. 418 const PointerType *PT = dyn_cast<PointerType>(FPT->getArgType(i)); 419 if (!PT) 420 return false; 421 422 // Verify that the argument is a 'char*'. 423 if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy) 424 return false; 425 } 426 427 return true; 428} 429 430//===----------------------------------------------------------------------===// 431// Check: Linear congruent random number generators should not be used 432// Originally: <rdar://problem/63371000> 433// CWE-338: Use of cryptographically weak prng 434//===----------------------------------------------------------------------===// 435 436void WalkAST::checkCall_rand(const CallExpr *CE, const FunctionDecl *FD) { 437 if (!CheckRand) 438 return; 439 440 const FunctionProtoType *FTP 441 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens()); 442 if (!FTP) 443 return; 444 445 if (FTP->getNumArgs() == 1) { 446 // Is the argument an 'unsigned short *'? 447 // (Actually any integer type is allowed.) 448 const PointerType *PT = dyn_cast<PointerType>(FTP->getArgType(0)); 449 if (!PT) 450 return; 451 452 if (! PT->getPointeeType()->isIntegerType()) 453 return; 454 } 455 else if (FTP->getNumArgs() != 0) 456 return; 457 458 // Issue a warning. 459 llvm::SmallString<256> buf1; 460 llvm::raw_svector_ostream os1(buf1); 461 os1 << '\'' << FD << "' is a poor random number generator"; 462 463 llvm::SmallString<256> buf2; 464 llvm::raw_svector_ostream os2(buf2); 465 os2 << "Function '" << FD 466 << "' is obsolete because it implements a poor random number generator." 467 << " Use 'arc4random' instead"; 468 469 SourceRange R = CE->getCallee()->getSourceRange(); 470 BR.EmitBasicReport(os1.str(), "Security", os2.str(),CE->getLocStart(), &R, 1); 471} 472 473//===----------------------------------------------------------------------===// 474// Check: 'random' should not be used 475// Originally: <rdar://problem/63371000> 476//===----------------------------------------------------------------------===// 477 478void WalkAST::checkCall_random(const CallExpr *CE, const FunctionDecl *FD) { 479 if (!CheckRand) 480 return; 481 482 const FunctionProtoType *FTP 483 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens()); 484 if (!FTP) 485 return; 486 487 // Verify that the function takes no argument. 488 if (FTP->getNumArgs() != 0) 489 return; 490 491 // Issue a warning. 492 SourceRange R = CE->getCallee()->getSourceRange(); 493 BR.EmitBasicReport("'random' is not a secure random number generator", 494 "Security", 495 "The 'random' function produces a sequence of values that " 496 "an adversary may be able to predict. Use 'arc4random' " 497 "instead", CE->getLocStart(), &R, 1); 498} 499 500//===----------------------------------------------------------------------===// 501// Check: Should check whether privileges are dropped successfully. 502// Originally: <rdar://problem/6337132> 503//===----------------------------------------------------------------------===// 504 505void WalkAST::checkUncheckedReturnValue(CallExpr *CE) { 506 const FunctionDecl *FD = CE->getDirectCallee(); 507 if (!FD) 508 return; 509 510 if (II_setid[0] == NULL) { 511 static const char * const identifiers[num_setids] = { 512 "setuid", "setgid", "seteuid", "setegid", 513 "setreuid", "setregid" 514 }; 515 516 for (size_t i = 0; i < num_setids; i++) 517 II_setid[i] = &BR.getContext().Idents.get(identifiers[i]); 518 } 519 520 const IdentifierInfo *id = FD->getIdentifier(); 521 size_t identifierid; 522 523 for (identifierid = 0; identifierid < num_setids; identifierid++) 524 if (id == II_setid[identifierid]) 525 break; 526 527 if (identifierid >= num_setids) 528 return; 529 530 const FunctionProtoType *FTP 531 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens()); 532 if (!FTP) 533 return; 534 535 // Verify that the function takes one or two arguments (depending on 536 // the function). 537 if (FTP->getNumArgs() != (identifierid < 4 ? 1 : 2)) 538 return; 539 540 // The arguments must be integers. 541 for (unsigned i = 0; i < FTP->getNumArgs(); i++) 542 if (! FTP->getArgType(i)->isIntegerType()) 543 return; 544 545 // Issue a warning. 546 llvm::SmallString<256> buf1; 547 llvm::raw_svector_ostream os1(buf1); 548 os1 << "Return value is not checked in call to '" << FD << '\''; 549 550 llvm::SmallString<256> buf2; 551 llvm::raw_svector_ostream os2(buf2); 552 os2 << "The return value from the call to '" << FD 553 << "' is not checked. If an error occurs in '" << FD 554 << "', the following code may execute with unexpected privileges"; 555 556 SourceRange R = CE->getCallee()->getSourceRange(); 557 BR.EmitBasicReport(os1.str(), "Security", os2.str(),CE->getLocStart(), &R, 1); 558} 559 560//===----------------------------------------------------------------------===// 561// SecuritySyntaxChecker 562//===----------------------------------------------------------------------===// 563 564namespace { 565class SecuritySyntaxChecker : public Checker<check::ASTCodeBody> { 566public: 567 void checkASTCodeBody(const Decl *D, AnalysisManager& mgr, 568 BugReporter &BR) const { 569 WalkAST walker(BR); 570 walker.Visit(D->getBody()); 571 } 572}; 573} 574 575void ento::registerSecuritySyntaxChecker(CheckerManager &mgr) { 576 mgr.registerChecker<SecuritySyntaxChecker>(); 577} 578