CheckSecuritySyntaxOnly.cpp revision 9b663716449b618ba0390b1dbebc54fa8e971124
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 "clang/Basic/TargetInfo.h" 15#include "clang/StaticAnalyzer/Core/BugReporter/BugReporter.h" 16#include "clang/StaticAnalyzer/Checkers/LocalCheckers.h" 17#include "clang/AST/StmtVisitor.h" 18#include "llvm/Support/raw_ostream.h" 19 20using namespace clang; 21using namespace ento; 22 23static bool isArc4RandomAvailable(const ASTContext &Ctx) { 24 const llvm::Triple &T = Ctx.Target.getTriple(); 25 return T.getVendor() == llvm::Triple::Apple || 26 T.getOS() == llvm::Triple::FreeBSD || 27 T.getOS() == llvm::Triple::NetBSD || 28 T.getOS() == llvm::Triple::OpenBSD || 29 T.getOS() == llvm::Triple::DragonFly; 30} 31 32namespace { 33class WalkAST : public StmtVisitor<WalkAST> { 34 BugReporter &BR; 35 IdentifierInfo *II_gets; 36 IdentifierInfo *II_getpw; 37 IdentifierInfo *II_mktemp; 38 enum { num_rands = 9 }; 39 IdentifierInfo *II_rand[num_rands]; 40 IdentifierInfo *II_random; 41 enum { num_setids = 6 }; 42 IdentifierInfo *II_setid[num_setids]; 43 44 const bool CheckRand; 45 46public: 47 WalkAST(BugReporter &br) : BR(br), 48 II_gets(0), II_getpw(0), II_mktemp(0), 49 II_rand(), II_random(0), II_setid(), 50 CheckRand(isArc4RandomAvailable(BR.getContext())) {} 51 52 // Statement visitor methods. 53 void VisitCallExpr(CallExpr *CE); 54 void VisitForStmt(ForStmt *S); 55 void VisitCompoundStmt (CompoundStmt *S); 56 void VisitStmt(Stmt *S) { VisitChildren(S); } 57 58 void VisitChildren(Stmt *S); 59 60 // Helpers. 61 IdentifierInfo *GetIdentifier(IdentifierInfo *& II, const char *str); 62 63 // Checker-specific methods. 64 void CheckLoopConditionForFloat(const ForStmt *FS); 65 void CheckCall_gets(const CallExpr *CE, const FunctionDecl *FD); 66 void CheckCall_getpw(const CallExpr *CE, const FunctionDecl *FD); 67 void CheckCall_mktemp(const CallExpr *CE, const FunctionDecl *FD); 68 void CheckCall_rand(const CallExpr *CE, const FunctionDecl *FD); 69 void CheckCall_random(const CallExpr *CE, const FunctionDecl *FD); 70 void CheckUncheckedReturnValue(CallExpr *CE); 71}; 72} // end anonymous namespace 73 74//===----------------------------------------------------------------------===// 75// Helper methods. 76//===----------------------------------------------------------------------===// 77 78IdentifierInfo *WalkAST::GetIdentifier(IdentifierInfo *& II, const char *str) { 79 if (!II) 80 II = &BR.getContext().Idents.get(str); 81 82 return II; 83} 84 85//===----------------------------------------------------------------------===// 86// AST walking. 87//===----------------------------------------------------------------------===// 88 89void WalkAST::VisitChildren(Stmt *S) { 90 for (Stmt::child_iterator I = S->child_begin(), E = S->child_end(); I!=E; ++I) 91 if (Stmt *child = *I) 92 Visit(child); 93} 94 95void WalkAST::VisitCallExpr(CallExpr *CE) { 96 if (const FunctionDecl *FD = CE->getDirectCallee()) { 97 CheckCall_gets(CE, FD); 98 CheckCall_getpw(CE, FD); 99 CheckCall_mktemp(CE, FD); 100 if (CheckRand) { 101 CheckCall_rand(CE, FD); 102 CheckCall_random(CE, FD); 103 } 104 } 105 106 // Recurse and check children. 107 VisitChildren(CE); 108} 109 110void WalkAST::VisitCompoundStmt(CompoundStmt *S) { 111 for (Stmt::child_iterator I = S->child_begin(), E = S->child_end(); I!=E; ++I) 112 if (Stmt *child = *I) { 113 if (CallExpr *CE = dyn_cast<CallExpr>(child)) 114 CheckUncheckedReturnValue(CE); 115 Visit(child); 116 } 117} 118 119void WalkAST::VisitForStmt(ForStmt *FS) { 120 CheckLoopConditionForFloat(FS); 121 122 // Recurse and check children. 123 VisitChildren(FS); 124} 125 126//===----------------------------------------------------------------------===// 127// Check: floating poing variable used as loop counter. 128// Originally: <rdar://problem/6336718> 129// Implements: CERT security coding advisory FLP-30. 130//===----------------------------------------------------------------------===// 131 132static const DeclRefExpr* 133GetIncrementedVar(const Expr *expr, const VarDecl *x, const VarDecl *y) { 134 expr = expr->IgnoreParenCasts(); 135 136 if (const BinaryOperator *B = dyn_cast<BinaryOperator>(expr)) { 137 if (!(B->isAssignmentOp() || B->isCompoundAssignmentOp() || 138 B->getOpcode() == BO_Comma)) 139 return NULL; 140 141 if (const DeclRefExpr *lhs = GetIncrementedVar(B->getLHS(), x, y)) 142 return lhs; 143 144 if (const DeclRefExpr *rhs = GetIncrementedVar(B->getRHS(), x, y)) 145 return rhs; 146 147 return NULL; 148 } 149 150 if (const DeclRefExpr *DR = dyn_cast<DeclRefExpr>(expr)) { 151 const NamedDecl *ND = DR->getDecl(); 152 return ND == x || ND == y ? DR : NULL; 153 } 154 155 if (const UnaryOperator *U = dyn_cast<UnaryOperator>(expr)) 156 return U->isIncrementDecrementOp() 157 ? GetIncrementedVar(U->getSubExpr(), x, y) : NULL; 158 159 return NULL; 160} 161 162/// CheckLoopConditionForFloat - This check looks for 'for' statements that 163/// use a floating point variable as a loop counter. 164/// CERT: FLP30-C, FLP30-CPP. 165/// 166void WalkAST::CheckLoopConditionForFloat(const ForStmt *FS) { 167 // Does the loop have a condition? 168 const Expr *condition = FS->getCond(); 169 170 if (!condition) 171 return; 172 173 // Does the loop have an increment? 174 const Expr *increment = FS->getInc(); 175 176 if (!increment) 177 return; 178 179 // Strip away '()' and casts. 180 condition = condition->IgnoreParenCasts(); 181 increment = increment->IgnoreParenCasts(); 182 183 // Is the loop condition a comparison? 184 const BinaryOperator *B = dyn_cast<BinaryOperator>(condition); 185 186 if (!B) 187 return; 188 189 // Is this a comparison? 190 if (!(B->isRelationalOp() || B->isEqualityOp())) 191 return; 192 193 // Are we comparing variables? 194 const DeclRefExpr *drLHS = 195 dyn_cast<DeclRefExpr>(B->getLHS()->IgnoreParenLValueCasts()); 196 const DeclRefExpr *drRHS = 197 dyn_cast<DeclRefExpr>(B->getRHS()->IgnoreParenLValueCasts()); 198 199 // Does at least one of the variables have a floating point type? 200 drLHS = drLHS && drLHS->getType()->isRealFloatingType() ? drLHS : NULL; 201 drRHS = drRHS && drRHS->getType()->isRealFloatingType() ? drRHS : NULL; 202 203 if (!drLHS && !drRHS) 204 return; 205 206 const VarDecl *vdLHS = drLHS ? dyn_cast<VarDecl>(drLHS->getDecl()) : NULL; 207 const VarDecl *vdRHS = drRHS ? dyn_cast<VarDecl>(drRHS->getDecl()) : NULL; 208 209 if (!vdLHS && !vdRHS) 210 return; 211 212 // Does either variable appear in increment? 213 const DeclRefExpr *drInc = GetIncrementedVar(increment, vdLHS, vdRHS); 214 215 if (!drInc) 216 return; 217 218 // Emit the error. First figure out which DeclRefExpr in the condition 219 // referenced the compared variable. 220 const DeclRefExpr *drCond = vdLHS == drInc->getDecl() ? drLHS : drRHS; 221 222 llvm::SmallVector<SourceRange, 2> ranges; 223 llvm::SmallString<256> sbuf; 224 llvm::raw_svector_ostream os(sbuf); 225 226 os << "Variable '" << drCond->getDecl()->getName() 227 << "' with floating point type '" << drCond->getType().getAsString() 228 << "' should not be used as a loop counter"; 229 230 ranges.push_back(drCond->getSourceRange()); 231 ranges.push_back(drInc->getSourceRange()); 232 233 const char *bugType = "Floating point variable used as loop counter"; 234 BR.EmitBasicReport(bugType, "Security", os.str(), 235 FS->getLocStart(), ranges.data(), ranges.size()); 236} 237 238//===----------------------------------------------------------------------===// 239// Check: Any use of 'gets' is insecure. 240// Originally: <rdar://problem/6335715> 241// Implements (part of): 300-BSI (buildsecurityin.us-cert.gov) 242// CWE-242: Use of Inherently Dangerous Function 243//===----------------------------------------------------------------------===// 244 245void WalkAST::CheckCall_gets(const CallExpr *CE, const FunctionDecl *FD) { 246 if (FD->getIdentifier() != GetIdentifier(II_gets, "gets")) 247 return; 248 249 const FunctionProtoType *FPT 250 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens()); 251 if (!FPT) 252 return; 253 254 // Verify that the function takes a single argument. 255 if (FPT->getNumArgs() != 1) 256 return; 257 258 // Is the argument a 'char*'? 259 const PointerType *PT = dyn_cast<PointerType>(FPT->getArgType(0)); 260 if (!PT) 261 return; 262 263 if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy) 264 return; 265 266 // Issue a warning. 267 SourceRange R = CE->getCallee()->getSourceRange(); 268 BR.EmitBasicReport("Potential buffer overflow in call to 'gets'", 269 "Security", 270 "Call to function 'gets' is extremely insecure as it can " 271 "always result in a buffer overflow", 272 CE->getLocStart(), &R, 1); 273} 274 275//===----------------------------------------------------------------------===// 276// Check: Any use of 'getpwd' is insecure. 277// CWE-477: Use of Obsolete Functions 278//===----------------------------------------------------------------------===// 279 280void WalkAST::CheckCall_getpw(const CallExpr *CE, const FunctionDecl *FD) { 281 if (FD->getIdentifier() != GetIdentifier(II_getpw, "getpw")) 282 return; 283 284 const FunctionProtoType *FPT 285 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens()); 286 if (!FPT) 287 return; 288 289 // Verify that the function takes two arguments. 290 if (FPT->getNumArgs() != 2) 291 return; 292 293 // Verify the first argument type is integer. 294 if (!FPT->getArgType(0)->isIntegerType()) 295 return; 296 297 // Verify the second argument type is char*. 298 const PointerType *PT = dyn_cast<PointerType>(FPT->getArgType(1)); 299 if (!PT) 300 return; 301 302 if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy) 303 return; 304 305 // Issue a warning. 306 SourceRange R = CE->getCallee()->getSourceRange(); 307 BR.EmitBasicReport("Potential buffer overflow in call to 'getpw'", 308 "Security", 309 "The getpw() function is dangerous as it may overflow the " 310 "provided buffer. It is obsoleted by getpwuid().", 311 CE->getLocStart(), &R, 1); 312} 313 314//===----------------------------------------------------------------------===// 315// Check: Any use of 'mktemp' is insecure.It is obsoleted by mkstemp(). 316// CWE-377: Insecure Temporary File 317//===----------------------------------------------------------------------===// 318 319void WalkAST::CheckCall_mktemp(const CallExpr *CE, const FunctionDecl *FD) { 320 if (FD->getIdentifier() != GetIdentifier(II_mktemp, "mktemp")) 321 return; 322 323 const FunctionProtoType *FPT 324 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens()); 325 if(!FPT) 326 return; 327 328 // Verify that the funcion takes a single argument. 329 if (FPT->getNumArgs() != 1) 330 return; 331 332 // Verify that the argument is Pointer Type. 333 const PointerType *PT = dyn_cast<PointerType>(FPT->getArgType(0)); 334 if (!PT) 335 return; 336 337 // Verify that the argument is a 'char*'. 338 if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy) 339 return; 340 341 // Issue a waring. 342 SourceRange R = CE->getCallee()->getSourceRange(); 343 BR.EmitBasicReport("Potential insecure temporary file in call 'mktemp'", 344 "Security", 345 "Call to function 'mktemp' is insecure as it always " 346 "creates or uses insecure temporary file. Use 'mkstemp' instead", 347 CE->getLocStart(), &R, 1); 348} 349 350//===----------------------------------------------------------------------===// 351// Check: Linear congruent random number generators should not be used 352// Originally: <rdar://problem/63371000> 353// CWE-338: Use of cryptographically weak prng 354//===----------------------------------------------------------------------===// 355 356void WalkAST::CheckCall_rand(const CallExpr *CE, const FunctionDecl *FD) { 357 if (II_rand[0] == NULL) { 358 // This check applies to these functions 359 static const char * const identifiers[num_rands] = { 360 "drand48", "erand48", "jrand48", "lrand48", "mrand48", "nrand48", 361 "lcong48", 362 "rand", "rand_r" 363 }; 364 365 for (size_t i = 0; i < num_rands; i++) 366 II_rand[i] = &BR.getContext().Idents.get(identifiers[i]); 367 } 368 369 const IdentifierInfo *id = FD->getIdentifier(); 370 size_t identifierid; 371 372 for (identifierid = 0; identifierid < num_rands; identifierid++) 373 if (id == II_rand[identifierid]) 374 break; 375 376 if (identifierid >= num_rands) 377 return; 378 379 const FunctionProtoType *FTP 380 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens()); 381 if (!FTP) 382 return; 383 384 if (FTP->getNumArgs() == 1) { 385 // Is the argument an 'unsigned short *'? 386 // (Actually any integer type is allowed.) 387 const PointerType *PT = dyn_cast<PointerType>(FTP->getArgType(0)); 388 if (!PT) 389 return; 390 391 if (! PT->getPointeeType()->isIntegerType()) 392 return; 393 } 394 else if (FTP->getNumArgs() != 0) 395 return; 396 397 // Issue a warning. 398 llvm::SmallString<256> buf1; 399 llvm::raw_svector_ostream os1(buf1); 400 os1 << '\'' << FD << "' is a poor random number generator"; 401 402 llvm::SmallString<256> buf2; 403 llvm::raw_svector_ostream os2(buf2); 404 os2 << "Function '" << FD 405 << "' is obsolete because it implements a poor random number generator." 406 << " Use 'arc4random' instead"; 407 408 SourceRange R = CE->getCallee()->getSourceRange(); 409 BR.EmitBasicReport(os1.str(), "Security", os2.str(),CE->getLocStart(), &R, 1); 410} 411 412//===----------------------------------------------------------------------===// 413// Check: 'random' should not be used 414// Originally: <rdar://problem/63371000> 415//===----------------------------------------------------------------------===// 416 417void WalkAST::CheckCall_random(const CallExpr *CE, const FunctionDecl *FD) { 418 if (FD->getIdentifier() != GetIdentifier(II_random, "random")) 419 return; 420 421 const FunctionProtoType *FTP 422 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens()); 423 if (!FTP) 424 return; 425 426 // Verify that the function takes no argument. 427 if (FTP->getNumArgs() != 0) 428 return; 429 430 // Issue a warning. 431 SourceRange R = CE->getCallee()->getSourceRange(); 432 BR.EmitBasicReport("'random' is not a secure random number generator", 433 "Security", 434 "The 'random' function produces a sequence of values that " 435 "an adversary may be able to predict. Use 'arc4random' " 436 "instead", CE->getLocStart(), &R, 1); 437} 438 439//===----------------------------------------------------------------------===// 440// Check: Should check whether privileges are dropped successfully. 441// Originally: <rdar://problem/6337132> 442//===----------------------------------------------------------------------===// 443 444void WalkAST::CheckUncheckedReturnValue(CallExpr *CE) { 445 const FunctionDecl *FD = CE->getDirectCallee(); 446 if (!FD) 447 return; 448 449 if (II_setid[0] == NULL) { 450 static const char * const identifiers[num_setids] = { 451 "setuid", "setgid", "seteuid", "setegid", 452 "setreuid", "setregid" 453 }; 454 455 for (size_t i = 0; i < num_setids; i++) 456 II_setid[i] = &BR.getContext().Idents.get(identifiers[i]); 457 } 458 459 const IdentifierInfo *id = FD->getIdentifier(); 460 size_t identifierid; 461 462 for (identifierid = 0; identifierid < num_setids; identifierid++) 463 if (id == II_setid[identifierid]) 464 break; 465 466 if (identifierid >= num_setids) 467 return; 468 469 const FunctionProtoType *FTP 470 = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens()); 471 if (!FTP) 472 return; 473 474 // Verify that the function takes one or two arguments (depending on 475 // the function). 476 if (FTP->getNumArgs() != (identifierid < 4 ? 1 : 2)) 477 return; 478 479 // The arguments must be integers. 480 for (unsigned i = 0; i < FTP->getNumArgs(); i++) 481 if (! FTP->getArgType(i)->isIntegerType()) 482 return; 483 484 // Issue a warning. 485 llvm::SmallString<256> buf1; 486 llvm::raw_svector_ostream os1(buf1); 487 os1 << "Return value is not checked in call to '" << FD << '\''; 488 489 llvm::SmallString<256> buf2; 490 llvm::raw_svector_ostream os2(buf2); 491 os2 << "The return value from the call to '" << FD 492 << "' is not checked. If an error occurs in '" << FD 493 << "', the following code may execute with unexpected privileges"; 494 495 SourceRange R = CE->getCallee()->getSourceRange(); 496 BR.EmitBasicReport(os1.str(), "Security", os2.str(),CE->getLocStart(), &R, 1); 497} 498 499//===----------------------------------------------------------------------===// 500// Entry point for check. 501//===----------------------------------------------------------------------===// 502 503void ento::CheckSecuritySyntaxOnly(const Decl *D, BugReporter &BR) { 504 WalkAST walker(BR); 505 walker.Visit(D->getBody()); 506} 507