lib/Checker/CheckSecuritySyntaxOnly.cpp

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