CheckSecuritySyntaxOnly.cpp revision c2dace11190e42d7cdd3c1b3bd2ecc8593f8e13e
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 IdentifierInfo *GetIdentifier(IdentifierInfo *& II, const char *str); 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// Helper methods. 75//===----------------------------------------------------------------------===// 76 77IdentifierInfo *WalkAST::GetIdentifier(IdentifierInfo *& II, const char *str) { 78 if (!II) 79 II = &BR.getContext().Idents.get(str); 80 81 return II; 82} 83 84//===----------------------------------------------------------------------===// 85// AST walking. 86//===----------------------------------------------------------------------===// 87 88void WalkAST::VisitChildren(Stmt *S) { 89 for (Stmt::child_iterator I = S->child_begin(), E = S->child_end(); I!=E; ++I) 90 if (Stmt *child = *I) 91 Visit(child); 92} 93 94void WalkAST::VisitCallExpr(CallExpr *CE) { 95 // Get the callee. 96 const FunctionDecl *FD = CE->getDirectCallee(); 97 98 if (!FD) 99 return; 100 101 // Get the name of the callee. If it's a builtin, strip off the prefix. 102 IdentifierInfo *II = FD->getIdentifier(); 103 if (!II) // if no identifier, not a simple C function 104 return; 105 llvm::StringRef Name = II->getName(); 106 if (Name.startswith("__builtin_")) 107 Name = Name.substr(10); 108 109 // Set the evaluation function by switching on the callee name. 110 FnCheck evalFunction = llvm::StringSwitch<FnCheck>(Name) 111 .Case("gets", &WalkAST::CheckCall_gets) 112 .Case("getpw", &WalkAST::CheckCall_getpw) 113 .Case("mktemp", &WalkAST::CheckCall_mktemp) 114 .Cases("strcpy", "__strcpy_chk", &WalkAST::CheckCall_strcpy) 115 .Case("drand48", &WalkAST::CheckCall_rand) 116 .Case("erand48", &WalkAST::CheckCall_rand) 117 .Case("jrand48", &WalkAST::CheckCall_rand) 118 .Case("lrand48", &WalkAST::CheckCall_rand) 119 .Case("mrand48", &WalkAST::CheckCall_rand) 120 .Case("nrand48", &WalkAST::CheckCall_rand) 121 .Case("lcong48", &WalkAST::CheckCall_rand) 122 .Case("rand", &WalkAST::CheckCall_rand) 123 .Case("rand_r", &WalkAST::CheckCall_rand) 124 .Case("random", &WalkAST::CheckCall_random) 125 .Default(NULL); 126 127 // If the callee isn't defined, it is not of security concern. 128 // Check and evaluate the call. 129 if (evalFunction) 130 (this->*evalFunction)(CE, FD); 131 132 // Recurse and check children. 133 VisitChildren(CE); 134} 135 136void WalkAST::VisitCompoundStmt(CompoundStmt *S) { 137 for (Stmt::child_iterator I = S->child_begin(), E = S->child_end(); I!=E; ++I) 138 if (Stmt *child = *I) { 139 if (CallExpr *CE = dyn_cast<CallExpr>(child)) 140 CheckUncheckedReturnValue(CE); 141 Visit(child); 142 } 143} 144 145void WalkAST::VisitForStmt(ForStmt *FS) { 146 CheckLoopConditionForFloat(FS); 147 148 // Recurse and check children. 149 VisitChildren(FS); 150} 151 152//===----------------------------------------------------------------------===// 153// Check: floating poing variable used as loop counter. 154// Originally: <rdar://problem/6336718> 155// Implements: CERT security coding advisory FLP-30. 156//===----------------------------------------------------------------------===// 157 158static const DeclRefExpr* 159GetIncrementedVar(const Expr *expr, const VarDecl *x, const VarDecl *y) { 160 expr = expr->IgnoreParenCasts(); 161 162 if (const BinaryOperator *B = dyn_cast<BinaryOperator>(expr)) { 163 if (!(B->isAssignmentOp() || B->isCompoundAssignmentOp() || 164 B->getOpcode() == BO_Comma)) 165 return NULL; 166 167 if (const DeclRefExpr *lhs = GetIncrementedVar(B->getLHS(), x, y)) 168 return lhs; 169 170 if (const DeclRefExpr *rhs = GetIncrementedVar(B->getRHS(), x, y)) 171 return rhs; 172 173 return NULL; 174 } 175 176 if (const DeclRefExpr *DR = dyn_cast<DeclRefExpr>(expr)) { 177 const NamedDecl *ND = DR->getDecl(); 178 return ND == x || ND == y ? DR : NULL; 179 } 180 181 if (const UnaryOperator *U = dyn_cast<UnaryOperator>(expr)) 182 return U->isIncrementDecrementOp() 183 ? GetIncrementedVar(U->getSubExpr(), x, y) : NULL; 184 185 return NULL; 186} 187 188/// CheckLoopConditionForFloat - This check looks for 'for' statements that 189/// use a floating point variable as a loop counter. 190/// CERT: FLP30-C, FLP30-CPP. 191/// 192void WalkAST::CheckLoopConditionForFloat(const ForStmt *FS) { 193 // Does the loop have a condition? 194 const Expr *condition = FS->getCond(); 195 196 if (!condition) 197 return; 198 199 // Does the loop have an increment? 200 const Expr *increment = FS->getInc(); 201 202 if (!increment) 203 return; 204 205 // Strip away '()' and casts. 206 condition = condition->IgnoreParenCasts(); 207 increment = increment->IgnoreParenCasts(); 208 209 // Is the loop condition a comparison? 210 const BinaryOperator *B = dyn_cast<BinaryOperator>(condition); 211 212 if (!B) 213 return; 214 215 // Is this a comparison? 216 if (!(B->isRelationalOp() || B->isEqualityOp())) 217 return; 218 219 // Are we comparing variables? 220 const DeclRefExpr *drLHS = 221 dyn_cast<DeclRefExpr>(B->getLHS()->IgnoreParenLValueCasts()); 222 const DeclRefExpr *drRHS = 223 dyn_cast<DeclRefExpr>(B->getRHS()->IgnoreParenLValueCasts()); 224 225 // Does at least one of the variables have a floating point type? 226 drLHS = drLHS && drLHS->getType()->isRealFloatingType() ? drLHS : NULL; 227 drRHS = drRHS && drRHS->getType()->isRealFloatingType() ? drRHS : NULL; 228 229 if (!drLHS && !drRHS) 230 return; 231 232 const VarDecl *vdLHS = drLHS ? dyn_cast<VarDecl>(drLHS->getDecl()) : NULL; 233 const VarDecl *vdRHS = drRHS ? dyn_cast<VarDecl>(drRHS->getDecl()) : NULL; 234 235 if (!vdLHS && !vdRHS) 236 return; 237 238 // Does either variable appear in increment? 239 const DeclRefExpr *drInc = GetIncrementedVar(increment, vdLHS, vdRHS); 240 241 if (!drInc) 242 return; 243 244 // Emit the error. First figure out which DeclRefExpr in the condition 245 // referenced the compared variable. 246 const DeclRefExpr *drCond = vdLHS == drInc->getDecl() ? drLHS : drRHS; 247 248 llvm::SmallVector<SourceRange, 2> ranges; 249 llvm::SmallString<256> sbuf; 250 llvm::raw_svector_ostream os(sbuf); 251 252 os << "Variable '" << drCond->getDecl()->getName() 253 << "' with floating point type '" << drCond->getType().getAsString() 254 << "' should not be used as a loop counter"; 255 256 ranges.push_back(drCond->getSourceRange()); 257 ranges.push_back(drInc->getSourceRange()); 258 259 const char *bugType = "Floating point variable used as loop counter"; 260 BR.EmitBasicReport(bugType, "Security", os.str(), 261 FS->getLocStart(), ranges.data(), ranges.size()); 262} 263 264//===----------------------------------------------------------------------===// 265// Check: Any use of 'gets' is insecure. 266// Originally: <rdar://problem/6335715> 267// Implements (part of): 300-BSI (buildsecurityin.us-cert.gov) 268// CWE-242: Use of Inherently Dangerous Function 269//===----------------------------------------------------------------------===// 270 271void WalkAST::CheckCall_gets(const CallExpr *CE, const FunctionDecl *FD) { 272 const FunctionProtoType *FPT 273 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens()); 274 if (!FPT) 275 return; 276 277 // Verify that the function takes a single argument. 278 if (FPT->getNumArgs() != 1) 279 return; 280 281 // Is the argument a 'char*'? 282 const PointerType *PT = dyn_cast<PointerType>(FPT->getArgType(0)); 283 if (!PT) 284 return; 285 286 if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy) 287 return; 288 289 // Issue a warning. 290 SourceRange R = CE->getCallee()->getSourceRange(); 291 BR.EmitBasicReport("Potential buffer overflow in call to 'gets'", 292 "Security", 293 "Call to function 'gets' is extremely insecure as it can " 294 "always result in a buffer overflow", 295 CE->getLocStart(), &R, 1); 296} 297 298//===----------------------------------------------------------------------===// 299// Check: Any use of 'getpwd' is insecure. 300// CWE-477: Use of Obsolete Functions 301//===----------------------------------------------------------------------===// 302 303void WalkAST::CheckCall_getpw(const CallExpr *CE, const FunctionDecl *FD) { 304 const FunctionProtoType *FPT 305 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens()); 306 if (!FPT) 307 return; 308 309 // Verify that the function takes two arguments. 310 if (FPT->getNumArgs() != 2) 311 return; 312 313 // Verify the first argument type is integer. 314 if (!FPT->getArgType(0)->isIntegerType()) 315 return; 316 317 // Verify the second argument type is char*. 318 const PointerType *PT = dyn_cast<PointerType>(FPT->getArgType(1)); 319 if (!PT) 320 return; 321 322 if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy) 323 return; 324 325 // Issue a warning. 326 SourceRange R = CE->getCallee()->getSourceRange(); 327 BR.EmitBasicReport("Potential buffer overflow in call to 'getpw'", 328 "Security", 329 "The getpw() function is dangerous as it may overflow the " 330 "provided buffer. It is obsoleted by getpwuid().", 331 CE->getLocStart(), &R, 1); 332} 333 334//===----------------------------------------------------------------------===// 335// Check: Any use of 'mktemp' is insecure.It is obsoleted by mkstemp(). 336// CWE-377: Insecure Temporary File 337//===----------------------------------------------------------------------===// 338 339void WalkAST::CheckCall_mktemp(const CallExpr *CE, const FunctionDecl *FD) { 340 const FunctionProtoType *FPT 341 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens()); 342 if(!FPT) 343 return; 344 345 // Verify that the function takes a single argument. 346 if (FPT->getNumArgs() != 1) 347 return; 348 349 // Verify that the argument is Pointer Type. 350 const PointerType *PT = dyn_cast<PointerType>(FPT->getArgType(0)); 351 if (!PT) 352 return; 353 354 // Verify that the argument is a 'char*'. 355 if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy) 356 return; 357 358 // Issue a waring. 359 SourceRange R = CE->getCallee()->getSourceRange(); 360 BR.EmitBasicReport("Potential insecure temporary file in call 'mktemp'", 361 "Security", 362 "Call to function 'mktemp' is insecure as it always " 363 "creates or uses insecure temporary file. Use 'mkstemp' instead", 364 CE->getLocStart(), &R, 1); 365} 366 367//===----------------------------------------------------------------------===// 368// Check: Any use of 'strcpy' is insecure. 369// 370// CWE-119: Improper Restriction of Operations within 371// the Bounds of a Memory Buffer 372//===----------------------------------------------------------------------===// 373void WalkAST::CheckCall_strcpy(const CallExpr *CE, const FunctionDecl *FD) { 374 const FunctionProtoType *FPT 375 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens()); 376 if (!FPT) 377 return; 378 379 // Verify the function takes two arguments 380 int numArgs = FPT->getNumArgs(); 381 if (numArgs != 2 && numArgs != 3) 382 return; 383 384 // Verify the type for both arguments 385 for (int i = 0; i < 2; i++) { 386 // Verify that the arguments are pointers 387 const PointerType *PT = dyn_cast<PointerType>(FPT->getArgType(i)); 388 if (!PT) 389 return; 390 391 // Verify that the argument is a 'char*'. 392 if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy) 393 return; 394 } 395 396 // Issue a warning 397 SourceRange R = CE->getCallee()->getSourceRange(); 398 BR.EmitBasicReport("Potential insecure memory buffer bounds restriction in " 399 "call 'strcpy'", 400 "Security", 401 "Call to function 'strcpy' is insecure as it does not " 402 "provide bounding of the memory buffer. Replace " 403 "unbounded copy functions with analogous functions that " 404 "support length arguments such as 'strncpy'. CWE-119.", 405 CE->getLocStart(), &R, 1); 406} 407 408//===----------------------------------------------------------------------===// 409// Check: Linear congruent random number generators should not be used 410// Originally: <rdar://problem/63371000> 411// CWE-338: Use of cryptographically weak prng 412//===----------------------------------------------------------------------===// 413 414void WalkAST::CheckCall_rand(const CallExpr *CE, const FunctionDecl *FD) { 415 if (!CheckRand) 416 return; 417 418 const FunctionProtoType *FTP 419 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens()); 420 if (!FTP) 421 return; 422 423 if (FTP->getNumArgs() == 1) { 424 // Is the argument an 'unsigned short *'? 425 // (Actually any integer type is allowed.) 426 const PointerType *PT = dyn_cast<PointerType>(FTP->getArgType(0)); 427 if (!PT) 428 return; 429 430 if (! PT->getPointeeType()->isIntegerType()) 431 return; 432 } 433 else if (FTP->getNumArgs() != 0) 434 return; 435 436 // Issue a warning. 437 llvm::SmallString<256> buf1; 438 llvm::raw_svector_ostream os1(buf1); 439 os1 << '\'' << FD << "' is a poor random number generator"; 440 441 llvm::SmallString<256> buf2; 442 llvm::raw_svector_ostream os2(buf2); 443 os2 << "Function '" << FD 444 << "' is obsolete because it implements a poor random number generator." 445 << " Use 'arc4random' instead"; 446 447 SourceRange R = CE->getCallee()->getSourceRange(); 448 BR.EmitBasicReport(os1.str(), "Security", os2.str(),CE->getLocStart(), &R, 1); 449} 450 451//===----------------------------------------------------------------------===// 452// Check: 'random' should not be used 453// Originally: <rdar://problem/63371000> 454//===----------------------------------------------------------------------===// 455 456void WalkAST::CheckCall_random(const CallExpr *CE, const FunctionDecl *FD) { 457 if (!CheckRand) 458 return; 459 460 const FunctionProtoType *FTP 461 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens()); 462 if (!FTP) 463 return; 464 465 // Verify that the function takes no argument. 466 if (FTP->getNumArgs() != 0) 467 return; 468 469 // Issue a warning. 470 SourceRange R = CE->getCallee()->getSourceRange(); 471 BR.EmitBasicReport("'random' is not a secure random number generator", 472 "Security", 473 "The 'random' function produces a sequence of values that " 474 "an adversary may be able to predict. Use 'arc4random' " 475 "instead", CE->getLocStart(), &R, 1); 476} 477 478//===----------------------------------------------------------------------===// 479// Check: Should check whether privileges are dropped successfully. 480// Originally: <rdar://problem/6337132> 481//===----------------------------------------------------------------------===// 482 483void WalkAST::CheckUncheckedReturnValue(CallExpr *CE) { 484 const FunctionDecl *FD = CE->getDirectCallee(); 485 if (!FD) 486 return; 487 488 if (II_setid[0] == NULL) { 489 static const char * const identifiers[num_setids] = { 490 "setuid", "setgid", "seteuid", "setegid", 491 "setreuid", "setregid" 492 }; 493 494 for (size_t i = 0; i < num_setids; i++) 495 II_setid[i] = &BR.getContext().Idents.get(identifiers[i]); 496 } 497 498 const IdentifierInfo *id = FD->getIdentifier(); 499 size_t identifierid; 500 501 for (identifierid = 0; identifierid < num_setids; identifierid++) 502 if (id == II_setid[identifierid]) 503 break; 504 505 if (identifierid >= num_setids) 506 return; 507 508 const FunctionProtoType *FTP 509 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens()); 510 if (!FTP) 511 return; 512 513 // Verify that the function takes one or two arguments (depending on 514 // the function). 515 if (FTP->getNumArgs() != (identifierid < 4 ? 1 : 2)) 516 return; 517 518 // The arguments must be integers. 519 for (unsigned i = 0; i < FTP->getNumArgs(); i++) 520 if (! FTP->getArgType(i)->isIntegerType()) 521 return; 522 523 // Issue a warning. 524 llvm::SmallString<256> buf1; 525 llvm::raw_svector_ostream os1(buf1); 526 os1 << "Return value is not checked in call to '" << FD << '\''; 527 528 llvm::SmallString<256> buf2; 529 llvm::raw_svector_ostream os2(buf2); 530 os2 << "The return value from the call to '" << FD 531 << "' is not checked. If an error occurs in '" << FD 532 << "', the following code may execute with unexpected privileges"; 533 534 SourceRange R = CE->getCallee()->getSourceRange(); 535 BR.EmitBasicReport(os1.str(), "Security", os2.str(),CE->getLocStart(), &R, 1); 536} 537 538//===----------------------------------------------------------------------===// 539// SecuritySyntaxChecker 540//===----------------------------------------------------------------------===// 541 542namespace { 543class SecuritySyntaxChecker : public Checker<check::ASTCodeBody> { 544public: 545 void checkASTCodeBody(const Decl *D, AnalysisManager& mgr, 546 BugReporter &BR) const { 547 WalkAST walker(BR); 548 walker.Visit(D->getBody()); 549 } 550}; 551} 552 553void ento::registerSecuritySyntaxChecker(CheckerManager &mgr) { 554 mgr.registerChecker<SecuritySyntaxChecker>(); 555} 556