clang  3.7.0
CheckSecuritySyntaxOnly.cpp
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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/AST/StmtVisitor.h"
17 #include "clang/Basic/TargetInfo.h"
21 #include "llvm/ADT/SmallString.h"
22 #include "llvm/ADT/StringSwitch.h"
23 #include "llvm/Support/raw_ostream.h"
24 
25 using namespace clang;
26 using namespace ento;
27 
28 static bool isArc4RandomAvailable(const ASTContext &Ctx) {
29  const llvm::Triple &T = Ctx.getTargetInfo().getTriple();
30  return T.getVendor() == llvm::Triple::Apple ||
31  T.getOS() == llvm::Triple::CloudABI ||
32  T.getOS() == llvm::Triple::FreeBSD ||
33  T.getOS() == llvm::Triple::NetBSD ||
34  T.getOS() == llvm::Triple::OpenBSD ||
35  T.getOS() == llvm::Triple::Bitrig ||
36  T.getOS() == llvm::Triple::DragonFly;
37 }
38 
39 namespace {
40 struct ChecksFilter {
41  DefaultBool check_gets;
42  DefaultBool check_getpw;
43  DefaultBool check_mktemp;
44  DefaultBool check_mkstemp;
45  DefaultBool check_strcpy;
46  DefaultBool check_rand;
47  DefaultBool check_vfork;
48  DefaultBool check_FloatLoopCounter;
49  DefaultBool check_UncheckedReturn;
50 
51  CheckName checkName_gets;
52  CheckName checkName_getpw;
53  CheckName checkName_mktemp;
54  CheckName checkName_mkstemp;
55  CheckName checkName_strcpy;
56  CheckName checkName_rand;
57  CheckName checkName_vfork;
58  CheckName checkName_FloatLoopCounter;
59  CheckName checkName_UncheckedReturn;
60 };
61 
62 class WalkAST : public StmtVisitor<WalkAST> {
63  BugReporter &BR;
65  enum { num_setids = 6 };
66  IdentifierInfo *II_setid[num_setids];
67 
68  const bool CheckRand;
69  const ChecksFilter &filter;
70 
71 public:
72  WalkAST(BugReporter &br, AnalysisDeclContext* ac,
73  const ChecksFilter &f)
74  : BR(br), AC(ac), II_setid(),
75  CheckRand(isArc4RandomAvailable(BR.getContext())),
76  filter(f) {}
77 
78  // Statement visitor methods.
79  void VisitCallExpr(CallExpr *CE);
80  void VisitForStmt(ForStmt *S);
81  void VisitCompoundStmt (CompoundStmt *S);
82  void VisitStmt(Stmt *S) { VisitChildren(S); }
83 
84  void VisitChildren(Stmt *S);
85 
86  // Helpers.
87  bool checkCall_strCommon(const CallExpr *CE, const FunctionDecl *FD);
88 
89  typedef void (WalkAST::*FnCheck)(const CallExpr *,
90  const FunctionDecl *);
91 
92  // Checker-specific methods.
93  void checkLoopConditionForFloat(const ForStmt *FS);
94  void checkCall_gets(const CallExpr *CE, const FunctionDecl *FD);
95  void checkCall_getpw(const CallExpr *CE, const FunctionDecl *FD);
96  void checkCall_mktemp(const CallExpr *CE, const FunctionDecl *FD);
97  void checkCall_mkstemp(const CallExpr *CE, const FunctionDecl *FD);
98  void checkCall_strcpy(const CallExpr *CE, const FunctionDecl *FD);
99  void checkCall_strcat(const CallExpr *CE, const FunctionDecl *FD);
100  void checkCall_rand(const CallExpr *CE, const FunctionDecl *FD);
101  void checkCall_random(const CallExpr *CE, const FunctionDecl *FD);
102  void checkCall_vfork(const CallExpr *CE, const FunctionDecl *FD);
103  void checkUncheckedReturnValue(CallExpr *CE);
104 };
105 } // end anonymous namespace
106 
107 //===----------------------------------------------------------------------===//
108 // AST walking.
109 //===----------------------------------------------------------------------===//
110 
111 void WalkAST::VisitChildren(Stmt *S) {
112  for (Stmt *Child : S->children())
113  if (Child)
114  Visit(Child);
115 }
116 
117 void WalkAST::VisitCallExpr(CallExpr *CE) {
118  // Get the callee.
119  const FunctionDecl *FD = CE->getDirectCallee();
120 
121  if (!FD)
122  return;
123 
124  // Get the name of the callee. If it's a builtin, strip off the prefix.
125  IdentifierInfo *II = FD->getIdentifier();
126  if (!II) // if no identifier, not a simple C function
127  return;
128  StringRef Name = II->getName();
129  if (Name.startswith("__builtin_"))
130  Name = Name.substr(10);
131 
132  // Set the evaluation function by switching on the callee name.
133  FnCheck evalFunction = llvm::StringSwitch<FnCheck>(Name)
134  .Case("gets", &WalkAST::checkCall_gets)
135  .Case("getpw", &WalkAST::checkCall_getpw)
136  .Case("mktemp", &WalkAST::checkCall_mktemp)
137  .Case("mkstemp", &WalkAST::checkCall_mkstemp)
138  .Case("mkdtemp", &WalkAST::checkCall_mkstemp)
139  .Case("mkstemps", &WalkAST::checkCall_mkstemp)
140  .Cases("strcpy", "__strcpy_chk", &WalkAST::checkCall_strcpy)
141  .Cases("strcat", "__strcat_chk", &WalkAST::checkCall_strcat)
142  .Case("drand48", &WalkAST::checkCall_rand)
143  .Case("erand48", &WalkAST::checkCall_rand)
144  .Case("jrand48", &WalkAST::checkCall_rand)
145  .Case("lrand48", &WalkAST::checkCall_rand)
146  .Case("mrand48", &WalkAST::checkCall_rand)
147  .Case("nrand48", &WalkAST::checkCall_rand)
148  .Case("lcong48", &WalkAST::checkCall_rand)
149  .Case("rand", &WalkAST::checkCall_rand)
150  .Case("rand_r", &WalkAST::checkCall_rand)
151  .Case("random", &WalkAST::checkCall_random)
152  .Case("vfork", &WalkAST::checkCall_vfork)
153  .Default(nullptr);
154 
155  // If the callee isn't defined, it is not of security concern.
156  // Check and evaluate the call.
157  if (evalFunction)
158  (this->*evalFunction)(CE, FD);
159 
160  // Recurse and check children.
161  VisitChildren(CE);
162 }
163 
164 void WalkAST::VisitCompoundStmt(CompoundStmt *S) {
165  for (Stmt *Child : S->children())
166  if (Child) {
167  if (CallExpr *CE = dyn_cast<CallExpr>(Child))
168  checkUncheckedReturnValue(CE);
169  Visit(Child);
170  }
171 }
172 
173 void WalkAST::VisitForStmt(ForStmt *FS) {
174  checkLoopConditionForFloat(FS);
175 
176  // Recurse and check children.
177  VisitChildren(FS);
178 }
179 
180 //===----------------------------------------------------------------------===//
181 // Check: floating poing variable used as loop counter.
182 // Originally: <rdar://problem/6336718>
183 // Implements: CERT security coding advisory FLP-30.
184 //===----------------------------------------------------------------------===//
185 
186 static const DeclRefExpr*
187 getIncrementedVar(const Expr *expr, const VarDecl *x, const VarDecl *y) {
188  expr = expr->IgnoreParenCasts();
189 
190  if (const BinaryOperator *B = dyn_cast<BinaryOperator>(expr)) {
191  if (!(B->isAssignmentOp() || B->isCompoundAssignmentOp() ||
192  B->getOpcode() == BO_Comma))
193  return nullptr;
194 
195  if (const DeclRefExpr *lhs = getIncrementedVar(B->getLHS(), x, y))
196  return lhs;
197 
198  if (const DeclRefExpr *rhs = getIncrementedVar(B->getRHS(), x, y))
199  return rhs;
200 
201  return nullptr;
202  }
203 
204  if (const DeclRefExpr *DR = dyn_cast<DeclRefExpr>(expr)) {
205  const NamedDecl *ND = DR->getDecl();
206  return ND == x || ND == y ? DR : nullptr;
207  }
208 
209  if (const UnaryOperator *U = dyn_cast<UnaryOperator>(expr))
210  return U->isIncrementDecrementOp()
211  ? getIncrementedVar(U->getSubExpr(), x, y) : nullptr;
212 
213  return nullptr;
214 }
215 
216 /// CheckLoopConditionForFloat - This check looks for 'for' statements that
217 /// use a floating point variable as a loop counter.
218 /// CERT: FLP30-C, FLP30-CPP.
219 ///
220 void WalkAST::checkLoopConditionForFloat(const ForStmt *FS) {
221  if (!filter.check_FloatLoopCounter)
222  return;
223 
224  // Does the loop have a condition?
225  const Expr *condition = FS->getCond();
226 
227  if (!condition)
228  return;
229 
230  // Does the loop have an increment?
231  const Expr *increment = FS->getInc();
232 
233  if (!increment)
234  return;
235 
236  // Strip away '()' and casts.
237  condition = condition->IgnoreParenCasts();
238  increment = increment->IgnoreParenCasts();
239 
240  // Is the loop condition a comparison?
241  const BinaryOperator *B = dyn_cast<BinaryOperator>(condition);
242 
243  if (!B)
244  return;
245 
246  // Is this a comparison?
247  if (!(B->isRelationalOp() || B->isEqualityOp()))
248  return;
249 
250  // Are we comparing variables?
251  const DeclRefExpr *drLHS =
252  dyn_cast<DeclRefExpr>(B->getLHS()->IgnoreParenLValueCasts());
253  const DeclRefExpr *drRHS =
254  dyn_cast<DeclRefExpr>(B->getRHS()->IgnoreParenLValueCasts());
255 
256  // Does at least one of the variables have a floating point type?
257  drLHS = drLHS && drLHS->getType()->isRealFloatingType() ? drLHS : nullptr;
258  drRHS = drRHS && drRHS->getType()->isRealFloatingType() ? drRHS : nullptr;
259 
260  if (!drLHS && !drRHS)
261  return;
262 
263  const VarDecl *vdLHS = drLHS ? dyn_cast<VarDecl>(drLHS->getDecl()) : nullptr;
264  const VarDecl *vdRHS = drRHS ? dyn_cast<VarDecl>(drRHS->getDecl()) : nullptr;
265 
266  if (!vdLHS && !vdRHS)
267  return;
268 
269  // Does either variable appear in increment?
270  const DeclRefExpr *drInc = getIncrementedVar(increment, vdLHS, vdRHS);
271 
272  if (!drInc)
273  return;
274 
275  // Emit the error. First figure out which DeclRefExpr in the condition
276  // referenced the compared variable.
277  assert(drInc->getDecl());
278  const DeclRefExpr *drCond = vdLHS == drInc->getDecl() ? drLHS : drRHS;
279 
281  SmallString<256> sbuf;
282  llvm::raw_svector_ostream os(sbuf);
283 
284  os << "Variable '" << drCond->getDecl()->getName()
285  << "' with floating point type '" << drCond->getType().getAsString()
286  << "' should not be used as a loop counter";
287 
288  ranges.push_back(drCond->getSourceRange());
289  ranges.push_back(drInc->getSourceRange());
290 
291  const char *bugType = "Floating point variable used as loop counter";
292 
293  PathDiagnosticLocation FSLoc =
294  PathDiagnosticLocation::createBegin(FS, BR.getSourceManager(), AC);
295  BR.EmitBasicReport(AC->getDecl(), filter.checkName_FloatLoopCounter,
296  bugType, "Security", os.str(),
297  FSLoc, ranges);
298 }
299 
300 //===----------------------------------------------------------------------===//
301 // Check: Any use of 'gets' is insecure.
302 // Originally: <rdar://problem/6335715>
303 // Implements (part of): 300-BSI (buildsecurityin.us-cert.gov)
304 // CWE-242: Use of Inherently Dangerous Function
305 //===----------------------------------------------------------------------===//
306 
307 void WalkAST::checkCall_gets(const CallExpr *CE, const FunctionDecl *FD) {
308  if (!filter.check_gets)
309  return;
310 
311  const FunctionProtoType *FPT = FD->getType()->getAs<FunctionProtoType>();
312  if (!FPT)
313  return;
314 
315  // Verify that the function takes a single argument.
316  if (FPT->getNumParams() != 1)
317  return;
318 
319  // Is the argument a 'char*'?
320  const PointerType *PT = FPT->getParamType(0)->getAs<PointerType>();
321  if (!PT)
322  return;
323 
324  if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
325  return;
326 
327  // Issue a warning.
328  PathDiagnosticLocation CELoc =
329  PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
330  BR.EmitBasicReport(AC->getDecl(), filter.checkName_gets,
331  "Potential buffer overflow in call to 'gets'",
332  "Security",
333  "Call to function 'gets' is extremely insecure as it can "
334  "always result in a buffer overflow",
335  CELoc, CE->getCallee()->getSourceRange());
336 }
337 
338 //===----------------------------------------------------------------------===//
339 // Check: Any use of 'getpwd' is insecure.
340 // CWE-477: Use of Obsolete Functions
341 //===----------------------------------------------------------------------===//
342 
343 void WalkAST::checkCall_getpw(const CallExpr *CE, const FunctionDecl *FD) {
344  if (!filter.check_getpw)
345  return;
346 
347  const FunctionProtoType *FPT = FD->getType()->getAs<FunctionProtoType>();
348  if (!FPT)
349  return;
350 
351  // Verify that the function takes two arguments.
352  if (FPT->getNumParams() != 2)
353  return;
354 
355  // Verify the first argument type is integer.
357  return;
358 
359  // Verify the second argument type is char*.
360  const PointerType *PT = FPT->getParamType(1)->getAs<PointerType>();
361  if (!PT)
362  return;
363 
364  if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
365  return;
366 
367  // Issue a warning.
368  PathDiagnosticLocation CELoc =
369  PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
370  BR.EmitBasicReport(AC->getDecl(), filter.checkName_getpw,
371  "Potential buffer overflow in call to 'getpw'",
372  "Security",
373  "The getpw() function is dangerous as it may overflow the "
374  "provided buffer. It is obsoleted by getpwuid().",
375  CELoc, CE->getCallee()->getSourceRange());
376 }
377 
378 //===----------------------------------------------------------------------===//
379 // Check: Any use of 'mktemp' is insecure. It is obsoleted by mkstemp().
380 // CWE-377: Insecure Temporary File
381 //===----------------------------------------------------------------------===//
382 
383 void WalkAST::checkCall_mktemp(const CallExpr *CE, const FunctionDecl *FD) {
384  if (!filter.check_mktemp) {
385  // Fall back to the security check of looking for enough 'X's in the
386  // format string, since that is a less severe warning.
387  checkCall_mkstemp(CE, FD);
388  return;
389  }
390 
391  const FunctionProtoType *FPT = FD->getType()->getAs<FunctionProtoType>();
392  if(!FPT)
393  return;
394 
395  // Verify that the function takes a single argument.
396  if (FPT->getNumParams() != 1)
397  return;
398 
399  // Verify that the argument is Pointer Type.
400  const PointerType *PT = FPT->getParamType(0)->getAs<PointerType>();
401  if (!PT)
402  return;
403 
404  // Verify that the argument is a 'char*'.
405  if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
406  return;
407 
408  // Issue a warning.
409  PathDiagnosticLocation CELoc =
410  PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
411  BR.EmitBasicReport(AC->getDecl(), filter.checkName_mktemp,
412  "Potential insecure temporary file in call 'mktemp'",
413  "Security",
414  "Call to function 'mktemp' is insecure as it always "
415  "creates or uses insecure temporary file. Use 'mkstemp' "
416  "instead",
417  CELoc, CE->getCallee()->getSourceRange());
418 }
419 
420 
421 //===----------------------------------------------------------------------===//
422 // Check: Use of 'mkstemp', 'mktemp', 'mkdtemp' should contain at least 6 X's.
423 //===----------------------------------------------------------------------===//
424 
425 void WalkAST::checkCall_mkstemp(const CallExpr *CE, const FunctionDecl *FD) {
426  if (!filter.check_mkstemp)
427  return;
428 
429  StringRef Name = FD->getIdentifier()->getName();
430  std::pair<signed, signed> ArgSuffix =
431  llvm::StringSwitch<std::pair<signed, signed> >(Name)
432  .Case("mktemp", std::make_pair(0,-1))
433  .Case("mkstemp", std::make_pair(0,-1))
434  .Case("mkdtemp", std::make_pair(0,-1))
435  .Case("mkstemps", std::make_pair(0,1))
436  .Default(std::make_pair(-1, -1));
437 
438  assert(ArgSuffix.first >= 0 && "Unsupported function");
439 
440  // Check if the number of arguments is consistent with out expectations.
441  unsigned numArgs = CE->getNumArgs();
442  if ((signed) numArgs <= ArgSuffix.first)
443  return;
444 
445  const StringLiteral *strArg =
446  dyn_cast<StringLiteral>(CE->getArg((unsigned)ArgSuffix.first)
447  ->IgnoreParenImpCasts());
448 
449  // Currently we only handle string literals. It is possible to do better,
450  // either by looking at references to const variables, or by doing real
451  // flow analysis.
452  if (!strArg || strArg->getCharByteWidth() != 1)
453  return;
454 
455  // Count the number of X's, taking into account a possible cutoff suffix.
456  StringRef str = strArg->getString();
457  unsigned numX = 0;
458  unsigned n = str.size();
459 
460  // Take into account the suffix.
461  unsigned suffix = 0;
462  if (ArgSuffix.second >= 0) {
463  const Expr *suffixEx = CE->getArg((unsigned)ArgSuffix.second);
464  llvm::APSInt Result;
465  if (!suffixEx->EvaluateAsInt(Result, BR.getContext()))
466  return;
467  // FIXME: Issue a warning.
468  if (Result.isNegative())
469  return;
470  suffix = (unsigned) Result.getZExtValue();
471  n = (n > suffix) ? n - suffix : 0;
472  }
473 
474  for (unsigned i = 0; i < n; ++i)
475  if (str[i] == 'X') ++numX;
476 
477  if (numX >= 6)
478  return;
479 
480  // Issue a warning.
481  PathDiagnosticLocation CELoc =
482  PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
483  SmallString<512> buf;
484  llvm::raw_svector_ostream out(buf);
485  out << "Call to '" << Name << "' should have at least 6 'X's in the"
486  " format string to be secure (" << numX << " 'X'";
487  if (numX != 1)
488  out << 's';
489  out << " seen";
490  if (suffix) {
491  out << ", " << suffix << " character";
492  if (suffix > 1)
493  out << 's';
494  out << " used as a suffix";
495  }
496  out << ')';
497  BR.EmitBasicReport(AC->getDecl(), filter.checkName_mkstemp,
498  "Insecure temporary file creation", "Security",
499  out.str(), CELoc, strArg->getSourceRange());
500 }
501 
502 //===----------------------------------------------------------------------===//
503 // Check: Any use of 'strcpy' is insecure.
504 //
505 // CWE-119: Improper Restriction of Operations within
506 // the Bounds of a Memory Buffer
507 //===----------------------------------------------------------------------===//
508 void WalkAST::checkCall_strcpy(const CallExpr *CE, const FunctionDecl *FD) {
509  if (!filter.check_strcpy)
510  return;
511 
512  if (!checkCall_strCommon(CE, FD))
513  return;
514 
515  // Issue a warning.
516  PathDiagnosticLocation CELoc =
517  PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
518  BR.EmitBasicReport(AC->getDecl(), filter.checkName_strcpy,
519  "Potential insecure memory buffer bounds restriction in "
520  "call 'strcpy'",
521  "Security",
522  "Call to function 'strcpy' is insecure as it does not "
523  "provide bounding of the memory buffer. Replace "
524  "unbounded copy functions with analogous functions that "
525  "support length arguments such as 'strlcpy'. CWE-119.",
526  CELoc, CE->getCallee()->getSourceRange());
527 }
528 
529 //===----------------------------------------------------------------------===//
530 // Check: Any use of 'strcat' is insecure.
531 //
532 // CWE-119: Improper Restriction of Operations within
533 // the Bounds of a Memory Buffer
534 //===----------------------------------------------------------------------===//
535 void WalkAST::checkCall_strcat(const CallExpr *CE, const FunctionDecl *FD) {
536  if (!filter.check_strcpy)
537  return;
538 
539  if (!checkCall_strCommon(CE, FD))
540  return;
541 
542  // Issue a warning.
543  PathDiagnosticLocation CELoc =
544  PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
545  BR.EmitBasicReport(AC->getDecl(), filter.checkName_strcpy,
546  "Potential insecure memory buffer bounds restriction in "
547  "call 'strcat'",
548  "Security",
549  "Call to function 'strcat' is insecure as it does not "
550  "provide bounding of the memory buffer. Replace "
551  "unbounded copy functions with analogous functions that "
552  "support length arguments such as 'strlcat'. CWE-119.",
553  CELoc, CE->getCallee()->getSourceRange());
554 }
555 
556 //===----------------------------------------------------------------------===//
557 // Common check for str* functions with no bounds parameters.
558 //===----------------------------------------------------------------------===//
559 bool WalkAST::checkCall_strCommon(const CallExpr *CE, const FunctionDecl *FD) {
560  const FunctionProtoType *FPT = FD->getType()->getAs<FunctionProtoType>();
561  if (!FPT)
562  return false;
563 
564  // Verify the function takes two arguments, three in the _chk version.
565  int numArgs = FPT->getNumParams();
566  if (numArgs != 2 && numArgs != 3)
567  return false;
568 
569  // Verify the type for both arguments.
570  for (int i = 0; i < 2; i++) {
571  // Verify that the arguments are pointers.
572  const PointerType *PT = FPT->getParamType(i)->getAs<PointerType>();
573  if (!PT)
574  return false;
575 
576  // Verify that the argument is a 'char*'.
577  if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
578  return false;
579  }
580 
581  return true;
582 }
583 
584 //===----------------------------------------------------------------------===//
585 // Check: Linear congruent random number generators should not be used
586 // Originally: <rdar://problem/63371000>
587 // CWE-338: Use of cryptographically weak prng
588 //===----------------------------------------------------------------------===//
589 
590 void WalkAST::checkCall_rand(const CallExpr *CE, const FunctionDecl *FD) {
591  if (!filter.check_rand || !CheckRand)
592  return;
593 
594  const FunctionProtoType *FTP = FD->getType()->getAs<FunctionProtoType>();
595  if (!FTP)
596  return;
597 
598  if (FTP->getNumParams() == 1) {
599  // Is the argument an 'unsigned short *'?
600  // (Actually any integer type is allowed.)
601  const PointerType *PT = FTP->getParamType(0)->getAs<PointerType>();
602  if (!PT)
603  return;
604 
606  return;
607  } else if (FTP->getNumParams() != 0)
608  return;
609 
610  // Issue a warning.
611  SmallString<256> buf1;
612  llvm::raw_svector_ostream os1(buf1);
613  os1 << '\'' << *FD << "' is a poor random number generator";
614 
615  SmallString<256> buf2;
616  llvm::raw_svector_ostream os2(buf2);
617  os2 << "Function '" << *FD
618  << "' is obsolete because it implements a poor random number generator."
619  << " Use 'arc4random' instead";
620 
621  PathDiagnosticLocation CELoc =
622  PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
623  BR.EmitBasicReport(AC->getDecl(), filter.checkName_rand, os1.str(),
624  "Security", os2.str(), CELoc,
625  CE->getCallee()->getSourceRange());
626 }
627 
628 //===----------------------------------------------------------------------===//
629 // Check: 'random' should not be used
630 // Originally: <rdar://problem/63371000>
631 //===----------------------------------------------------------------------===//
632 
633 void WalkAST::checkCall_random(const CallExpr *CE, const FunctionDecl *FD) {
634  if (!CheckRand || !filter.check_rand)
635  return;
636 
637  const FunctionProtoType *FTP = FD->getType()->getAs<FunctionProtoType>();
638  if (!FTP)
639  return;
640 
641  // Verify that the function takes no argument.
642  if (FTP->getNumParams() != 0)
643  return;
644 
645  // Issue a warning.
646  PathDiagnosticLocation CELoc =
647  PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
648  BR.EmitBasicReport(AC->getDecl(), filter.checkName_rand,
649  "'random' is not a secure random number generator",
650  "Security",
651  "The 'random' function produces a sequence of values that "
652  "an adversary may be able to predict. Use 'arc4random' "
653  "instead", CELoc, CE->getCallee()->getSourceRange());
654 }
655 
656 //===----------------------------------------------------------------------===//
657 // Check: 'vfork' should not be used.
658 // POS33-C: Do not use vfork().
659 //===----------------------------------------------------------------------===//
660 
661 void WalkAST::checkCall_vfork(const CallExpr *CE, const FunctionDecl *FD) {
662  if (!filter.check_vfork)
663  return;
664 
665  // All calls to vfork() are insecure, issue a warning.
666  PathDiagnosticLocation CELoc =
667  PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
668  BR.EmitBasicReport(AC->getDecl(), filter.checkName_vfork,
669  "Potential insecure implementation-specific behavior in "
670  "call 'vfork'",
671  "Security",
672  "Call to function 'vfork' is insecure as it can lead to "
673  "denial of service situations in the parent process. "
674  "Replace calls to vfork with calls to the safer "
675  "'posix_spawn' function",
676  CELoc, CE->getCallee()->getSourceRange());
677 }
678 
679 //===----------------------------------------------------------------------===//
680 // Check: Should check whether privileges are dropped successfully.
681 // Originally: <rdar://problem/6337132>
682 //===----------------------------------------------------------------------===//
683 
684 void WalkAST::checkUncheckedReturnValue(CallExpr *CE) {
685  if (!filter.check_UncheckedReturn)
686  return;
687 
688  const FunctionDecl *FD = CE->getDirectCallee();
689  if (!FD)
690  return;
691 
692  if (II_setid[0] == nullptr) {
693  static const char * const identifiers[num_setids] = {
694  "setuid", "setgid", "seteuid", "setegid",
695  "setreuid", "setregid"
696  };
697 
698  for (size_t i = 0; i < num_setids; i++)
699  II_setid[i] = &BR.getContext().Idents.get(identifiers[i]);
700  }
701 
702  const IdentifierInfo *id = FD->getIdentifier();
703  size_t identifierid;
704 
705  for (identifierid = 0; identifierid < num_setids; identifierid++)
706  if (id == II_setid[identifierid])
707  break;
708 
709  if (identifierid >= num_setids)
710  return;
711 
712  const FunctionProtoType *FTP = FD->getType()->getAs<FunctionProtoType>();
713  if (!FTP)
714  return;
715 
716  // Verify that the function takes one or two arguments (depending on
717  // the function).
718  if (FTP->getNumParams() != (identifierid < 4 ? 1 : 2))
719  return;
720 
721  // The arguments must be integers.
722  for (unsigned i = 0; i < FTP->getNumParams(); i++)
724  return;
725 
726  // Issue a warning.
727  SmallString<256> buf1;
728  llvm::raw_svector_ostream os1(buf1);
729  os1 << "Return value is not checked in call to '" << *FD << '\'';
730 
731  SmallString<256> buf2;
732  llvm::raw_svector_ostream os2(buf2);
733  os2 << "The return value from the call to '" << *FD
734  << "' is not checked. If an error occurs in '" << *FD
735  << "', the following code may execute with unexpected privileges";
736 
737  PathDiagnosticLocation CELoc =
738  PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
739  BR.EmitBasicReport(AC->getDecl(), filter.checkName_UncheckedReturn, os1.str(),
740  "Security", os2.str(), CELoc,
741  CE->getCallee()->getSourceRange());
742 }
743 
744 //===----------------------------------------------------------------------===//
745 // SecuritySyntaxChecker
746 //===----------------------------------------------------------------------===//
747 
748 namespace {
749 class SecuritySyntaxChecker : public Checker<check::ASTCodeBody> {
750 public:
751  ChecksFilter filter;
752 
753  void checkASTCodeBody(const Decl *D, AnalysisManager& mgr,
754  BugReporter &BR) const {
755  WalkAST walker(BR, mgr.getAnalysisDeclContext(D), filter);
756  walker.Visit(D->getBody());
757  }
758 };
759 }
760 
761 #define REGISTER_CHECKER(name) \
762  void ento::register##name(CheckerManager &mgr) { \
763  SecuritySyntaxChecker *checker = \
764  mgr.registerChecker<SecuritySyntaxChecker>(); \
765  checker->filter.check_##name = true; \
766  checker->filter.checkName_##name = mgr.getCurrentCheckName(); \
767  }
768 
769 REGISTER_CHECKER(gets)
770 REGISTER_CHECKER(getpw)
771 REGISTER_CHECKER(mkstemp)
772 REGISTER_CHECKER(mktemp)
773 REGISTER_CHECKER(strcpy)
774 REGISTER_CHECKER(rand)
775 REGISTER_CHECKER(vfork)
776 REGISTER_CHECKER(FloatLoopCounter)
777 REGISTER_CHECKER(UncheckedReturn)
778 
779 
Expr * getInc()
Definition: Stmt.h:1178
const internal::VariadicDynCastAllOfMatcher< Stmt, Expr > expr
Matches expressions.
Definition: ASTMatchers.h:1110
Expr * getArg(unsigned Arg)
getArg - Return the specified argument.
Definition: Expr.h:2216
IdentifierInfo * getIdentifier() const
Definition: Decl.h:163
A helper class which wraps a boolean value set to false by default.
Definition: Checker.h:523
const Expr * getCallee() const
Definition: Expr.h:2188
unsigned getNumParams() const
Definition: Type.h:3133
Holds long-lived AST nodes (such as types and decls) that can be referred to throughout the semantic ...
Definition: ASTContext.h:89
Expr * getLHS() const
Definition: Expr.h:2964
static bool isRelationalOp(Opcode Opc)
Definition: Expr.h:3001
bool isIntegralOrUnscopedEnumerationType() const
Determine whether this type is an integral or unscoped enumeration type.
Definition: Type.cpp:1616
static bool isEqualityOp(Opcode Opc)
Definition: Expr.h:3004
const TargetInfo & getTargetInfo() const
Definition: ASTContext.h:518
A builtin binary operation expression such as "x + y" or "x <= y".
Definition: Expr.h:2918
Expr * IgnoreParenCasts() LLVM_READONLY
Definition: Expr.cpp:2439
Expr * getCond()
Definition: Stmt.h:1177
child_range children()
Definition: Stmt.h:641
QualType getType() const
Definition: Decl.h:538
AnalysisDeclContext * getAnalysisDeclContext(const Decl *D)
QualType getParamType(unsigned i) const
Definition: Type.h:3134
bool isRealFloatingType() const
Floating point categories.
Definition: Type.cpp:1776
StringRef getName() const
Return the actual identifier string.
bool EvaluateAsInt(llvm::APSInt &Result, const ASTContext &Ctx, SideEffectsKind AllowSideEffects=SE_NoSideEffects) const
ValueDecl * getDecl()
Definition: Expr.h:994
The result type of a method or function.
static PathDiagnosticLocation createBegin(const Decl *D, const SourceManager &SM)
Create a location for the beginning of the declaration.
static const DeclRefExpr * getIncrementedVar(const Expr *expr, const VarDecl *x, const VarDecl *y)
#define REGISTER_CHECKER(name)
virtual Stmt * getBody() const
Definition: DeclBase.h:840
unsigned getCharByteWidth() const
Definition: Expr.h:1555
QualType getPointeeType() const
Definition: Type.h:2139
QualType getType() const
Definition: Expr.h:125
FunctionDecl * getDirectCallee()
If the callee is a FunctionDecl, return it. Otherwise return 0.
Definition: Expr.cpp:1184
StringRef getString() const
Definition: Expr.h:1521
const llvm::Triple & getTriple() const
Returns the target triple of the primary target.
unsigned getNumArgs() const
Definition: Expr.h:2205
Expr * IgnoreParenImpCasts() LLVM_READONLY
Definition: Expr.cpp:2526
const T * getAs() const
Definition: Type.h:5555
static __inline__ uint32_t uint32_t y
Definition: arm_acle.h:113
Expr * IgnoreParenLValueCasts() LLVM_READONLY
Definition: Expr.cpp:2486
QualType getUnqualifiedType() const
Retrieve the unqualified variant of the given type, removing as little sugar as possible.
Definition: Type.h:5096
Defines the clang::TargetInfo interface.
Expr * getRHS() const
Definition: Expr.h:2966
A reference to a declared variable, function, enum, etc. [C99 6.5.1p2].
Definition: Expr.h:899
static bool isArc4RandomAvailable(const ASTContext &Ctx)