clang  3.9.0
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 *, const FunctionDecl *);
90 
91  // Checker-specific methods.
92  void checkLoopConditionForFloat(const ForStmt *FS);
93  void checkCall_gets(const CallExpr *CE, const FunctionDecl *FD);
94  void checkCall_getpw(const CallExpr *CE, const FunctionDecl *FD);
95  void checkCall_mktemp(const CallExpr *CE, const FunctionDecl *FD);
96  void checkCall_mkstemp(const CallExpr *CE, const FunctionDecl *FD);
97  void checkCall_strcpy(const CallExpr *CE, const FunctionDecl *FD);
98  void checkCall_strcat(const CallExpr *CE, const FunctionDecl *FD);
99  void checkCall_rand(const CallExpr *CE, const FunctionDecl *FD);
100  void checkCall_random(const CallExpr *CE, const FunctionDecl *FD);
101  void checkCall_vfork(const CallExpr *CE, const FunctionDecl *FD);
102  void checkUncheckedReturnValue(CallExpr *CE);
103 };
104 } // end anonymous namespace
105 
106 //===----------------------------------------------------------------------===//
107 // AST walking.
108 //===----------------------------------------------------------------------===//
109 
110 void WalkAST::VisitChildren(Stmt *S) {
111  for (Stmt *Child : S->children())
112  if (Child)
113  Visit(Child);
114 }
115 
116 void WalkAST::VisitCallExpr(CallExpr *CE) {
117  // Get the callee.
118  const FunctionDecl *FD = CE->getDirectCallee();
119 
120  if (!FD)
121  return;
122 
123  // Get the name of the callee. If it's a builtin, strip off the prefix.
124  IdentifierInfo *II = FD->getIdentifier();
125  if (!II) // if no identifier, not a simple C function
126  return;
127  StringRef Name = II->getName();
128  if (Name.startswith("__builtin_"))
129  Name = Name.substr(10);
130 
131  // Set the evaluation function by switching on the callee name.
132  FnCheck evalFunction = llvm::StringSwitch<FnCheck>(Name)
133  .Case("gets", &WalkAST::checkCall_gets)
134  .Case("getpw", &WalkAST::checkCall_getpw)
135  .Case("mktemp", &WalkAST::checkCall_mktemp)
136  .Case("mkstemp", &WalkAST::checkCall_mkstemp)
137  .Case("mkdtemp", &WalkAST::checkCall_mkstemp)
138  .Case("mkstemps", &WalkAST::checkCall_mkstemp)
139  .Cases("strcpy", "__strcpy_chk", &WalkAST::checkCall_strcpy)
140  .Cases("strcat", "__strcat_chk", &WalkAST::checkCall_strcat)
141  .Case("drand48", &WalkAST::checkCall_rand)
142  .Case("erand48", &WalkAST::checkCall_rand)
143  .Case("jrand48", &WalkAST::checkCall_rand)
144  .Case("lrand48", &WalkAST::checkCall_rand)
145  .Case("mrand48", &WalkAST::checkCall_rand)
146  .Case("nrand48", &WalkAST::checkCall_rand)
147  .Case("lcong48", &WalkAST::checkCall_rand)
148  .Case("rand", &WalkAST::checkCall_rand)
149  .Case("rand_r", &WalkAST::checkCall_rand)
150  .Case("random", &WalkAST::checkCall_random)
151  .Case("vfork", &WalkAST::checkCall_vfork)
152  .Default(nullptr);
153 
154  // If the callee isn't defined, it is not of security concern.
155  // Check and evaluate the call.
156  if (evalFunction)
157  (this->*evalFunction)(CE, FD);
158 
159  // Recurse and check children.
160  VisitChildren(CE);
161 }
162 
163 void WalkAST::VisitCompoundStmt(CompoundStmt *S) {
164  for (Stmt *Child : S->children())
165  if (Child) {
166  if (CallExpr *CE = dyn_cast<CallExpr>(Child))
167  checkUncheckedReturnValue(CE);
168  Visit(Child);
169  }
170 }
171 
172 void WalkAST::VisitForStmt(ForStmt *FS) {
173  checkLoopConditionForFloat(FS);
174 
175  // Recurse and check children.
176  VisitChildren(FS);
177 }
178 
179 //===----------------------------------------------------------------------===//
180 // Check: floating poing variable used as loop counter.
181 // Originally: <rdar://problem/6336718>
182 // Implements: CERT security coding advisory FLP-30.
183 //===----------------------------------------------------------------------===//
184 
185 static const DeclRefExpr*
186 getIncrementedVar(const Expr *expr, const VarDecl *x, const VarDecl *y) {
187  expr = expr->IgnoreParenCasts();
188 
189  if (const BinaryOperator *B = dyn_cast<BinaryOperator>(expr)) {
190  if (!(B->isAssignmentOp() || B->isCompoundAssignmentOp() ||
191  B->getOpcode() == BO_Comma))
192  return nullptr;
193 
194  if (const DeclRefExpr *lhs = getIncrementedVar(B->getLHS(), x, y))
195  return lhs;
196 
197  if (const DeclRefExpr *rhs = getIncrementedVar(B->getRHS(), x, y))
198  return rhs;
199 
200  return nullptr;
201  }
202 
203  if (const DeclRefExpr *DR = dyn_cast<DeclRefExpr>(expr)) {
204  const NamedDecl *ND = DR->getDecl();
205  return ND == x || ND == y ? DR : nullptr;
206  }
207 
208  if (const UnaryOperator *U = dyn_cast<UnaryOperator>(expr))
209  return U->isIncrementDecrementOp()
210  ? getIncrementedVar(U->getSubExpr(), x, y) : nullptr;
211 
212  return nullptr;
213 }
214 
215 /// CheckLoopConditionForFloat - This check looks for 'for' statements that
216 /// use a floating point variable as a loop counter.
217 /// CERT: FLP30-C, FLP30-CPP.
218 ///
219 void WalkAST::checkLoopConditionForFloat(const ForStmt *FS) {
220  if (!filter.check_FloatLoopCounter)
221  return;
222 
223  // Does the loop have a condition?
224  const Expr *condition = FS->getCond();
225 
226  if (!condition)
227  return;
228 
229  // Does the loop have an increment?
230  const Expr *increment = FS->getInc();
231 
232  if (!increment)
233  return;
234 
235  // Strip away '()' and casts.
236  condition = condition->IgnoreParenCasts();
237  increment = increment->IgnoreParenCasts();
238 
239  // Is the loop condition a comparison?
240  const BinaryOperator *B = dyn_cast<BinaryOperator>(condition);
241 
242  if (!B)
243  return;
244 
245  // Is this a comparison?
246  if (!(B->isRelationalOp() || B->isEqualityOp()))
247  return;
248 
249  // Are we comparing variables?
250  const DeclRefExpr *drLHS =
251  dyn_cast<DeclRefExpr>(B->getLHS()->IgnoreParenLValueCasts());
252  const DeclRefExpr *drRHS =
253  dyn_cast<DeclRefExpr>(B->getRHS()->IgnoreParenLValueCasts());
254 
255  // Does at least one of the variables have a floating point type?
256  drLHS = drLHS && drLHS->getType()->isRealFloatingType() ? drLHS : nullptr;
257  drRHS = drRHS && drRHS->getType()->isRealFloatingType() ? drRHS : nullptr;
258 
259  if (!drLHS && !drRHS)
260  return;
261 
262  const VarDecl *vdLHS = drLHS ? dyn_cast<VarDecl>(drLHS->getDecl()) : nullptr;
263  const VarDecl *vdRHS = drRHS ? dyn_cast<VarDecl>(drRHS->getDecl()) : nullptr;
264 
265  if (!vdLHS && !vdRHS)
266  return;
267 
268  // Does either variable appear in increment?
269  const DeclRefExpr *drInc = getIncrementedVar(increment, vdLHS, vdRHS);
270 
271  if (!drInc)
272  return;
273 
274  // Emit the error. First figure out which DeclRefExpr in the condition
275  // referenced the compared variable.
276  assert(drInc->getDecl());
277  const DeclRefExpr *drCond = vdLHS == drInc->getDecl() ? drLHS : drRHS;
278 
280  SmallString<256> sbuf;
281  llvm::raw_svector_ostream os(sbuf);
282 
283  os << "Variable '" << drCond->getDecl()->getName()
284  << "' with floating point type '" << drCond->getType().getAsString()
285  << "' should not be used as a loop counter";
286 
287  ranges.push_back(drCond->getSourceRange());
288  ranges.push_back(drInc->getSourceRange());
289 
290  const char *bugType = "Floating point variable used as loop counter";
291 
292  PathDiagnosticLocation FSLoc =
293  PathDiagnosticLocation::createBegin(FS, BR.getSourceManager(), AC);
294  BR.EmitBasicReport(AC->getDecl(), filter.checkName_FloatLoopCounter,
295  bugType, "Security", os.str(),
296  FSLoc, ranges);
297 }
298 
299 //===----------------------------------------------------------------------===//
300 // Check: Any use of 'gets' is insecure.
301 // Originally: <rdar://problem/6335715>
302 // Implements (part of): 300-BSI (buildsecurityin.us-cert.gov)
303 // CWE-242: Use of Inherently Dangerous Function
304 //===----------------------------------------------------------------------===//
305 
306 void WalkAST::checkCall_gets(const CallExpr *CE, const FunctionDecl *FD) {
307  if (!filter.check_gets)
308  return;
309 
310  const FunctionProtoType *FPT = FD->getType()->getAs<FunctionProtoType>();
311  if (!FPT)
312  return;
313 
314  // Verify that the function takes a single argument.
315  if (FPT->getNumParams() != 1)
316  return;
317 
318  // Is the argument a 'char*'?
319  const PointerType *PT = FPT->getParamType(0)->getAs<PointerType>();
320  if (!PT)
321  return;
322 
323  if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
324  return;
325 
326  // Issue a warning.
327  PathDiagnosticLocation CELoc =
328  PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
329  BR.EmitBasicReport(AC->getDecl(), filter.checkName_gets,
330  "Potential buffer overflow in call to 'gets'",
331  "Security",
332  "Call to function 'gets' is extremely insecure as it can "
333  "always result in a buffer overflow",
334  CELoc, CE->getCallee()->getSourceRange());
335 }
336 
337 //===----------------------------------------------------------------------===//
338 // Check: Any use of 'getpwd' is insecure.
339 // CWE-477: Use of Obsolete Functions
340 //===----------------------------------------------------------------------===//
341 
342 void WalkAST::checkCall_getpw(const CallExpr *CE, const FunctionDecl *FD) {
343  if (!filter.check_getpw)
344  return;
345 
346  const FunctionProtoType *FPT = FD->getType()->getAs<FunctionProtoType>();
347  if (!FPT)
348  return;
349 
350  // Verify that the function takes two arguments.
351  if (FPT->getNumParams() != 2)
352  return;
353 
354  // Verify the first argument type is integer.
356  return;
357 
358  // Verify the second argument type is char*.
359  const PointerType *PT = FPT->getParamType(1)->getAs<PointerType>();
360  if (!PT)
361  return;
362 
363  if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
364  return;
365 
366  // Issue a warning.
367  PathDiagnosticLocation CELoc =
368  PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
369  BR.EmitBasicReport(AC->getDecl(), filter.checkName_getpw,
370  "Potential buffer overflow in call to 'getpw'",
371  "Security",
372  "The getpw() function is dangerous as it may overflow the "
373  "provided buffer. It is obsoleted by getpwuid().",
374  CELoc, CE->getCallee()->getSourceRange());
375 }
376 
377 //===----------------------------------------------------------------------===//
378 // Check: Any use of 'mktemp' is insecure. It is obsoleted by mkstemp().
379 // CWE-377: Insecure Temporary File
380 //===----------------------------------------------------------------------===//
381 
382 void WalkAST::checkCall_mktemp(const CallExpr *CE, const FunctionDecl *FD) {
383  if (!filter.check_mktemp) {
384  // Fall back to the security check of looking for enough 'X's in the
385  // format string, since that is a less severe warning.
386  checkCall_mkstemp(CE, FD);
387  return;
388  }
389 
390  const FunctionProtoType *FPT = FD->getType()->getAs<FunctionProtoType>();
391  if(!FPT)
392  return;
393 
394  // Verify that the function takes a single argument.
395  if (FPT->getNumParams() != 1)
396  return;
397 
398  // Verify that the argument is Pointer Type.
399  const PointerType *PT = FPT->getParamType(0)->getAs<PointerType>();
400  if (!PT)
401  return;
402 
403  // Verify that the argument is a 'char*'.
404  if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
405  return;
406 
407  // Issue a warning.
408  PathDiagnosticLocation CELoc =
409  PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
410  BR.EmitBasicReport(AC->getDecl(), filter.checkName_mktemp,
411  "Potential insecure temporary file in call 'mktemp'",
412  "Security",
413  "Call to function 'mktemp' is insecure as it always "
414  "creates or uses insecure temporary file. Use 'mkstemp' "
415  "instead",
416  CELoc, CE->getCallee()->getSourceRange());
417 }
418 
419 
420 //===----------------------------------------------------------------------===//
421 // Check: Use of 'mkstemp', 'mktemp', 'mkdtemp' should contain at least 6 X's.
422 //===----------------------------------------------------------------------===//
423 
424 void WalkAST::checkCall_mkstemp(const CallExpr *CE, const FunctionDecl *FD) {
425  if (!filter.check_mkstemp)
426  return;
427 
428  StringRef Name = FD->getIdentifier()->getName();
429  std::pair<signed, signed> ArgSuffix =
430  llvm::StringSwitch<std::pair<signed, signed> >(Name)
431  .Case("mktemp", std::make_pair(0,-1))
432  .Case("mkstemp", std::make_pair(0,-1))
433  .Case("mkdtemp", std::make_pair(0,-1))
434  .Case("mkstemps", std::make_pair(0,1))
435  .Default(std::make_pair(-1, -1));
436 
437  assert(ArgSuffix.first >= 0 && "Unsupported function");
438 
439  // Check if the number of arguments is consistent with out expectations.
440  unsigned numArgs = CE->getNumArgs();
441  if ((signed) numArgs <= ArgSuffix.first)
442  return;
443 
444  const StringLiteral *strArg =
445  dyn_cast<StringLiteral>(CE->getArg((unsigned)ArgSuffix.first)
446  ->IgnoreParenImpCasts());
447 
448  // Currently we only handle string literals. It is possible to do better,
449  // either by looking at references to const variables, or by doing real
450  // flow analysis.
451  if (!strArg || strArg->getCharByteWidth() != 1)
452  return;
453 
454  // Count the number of X's, taking into account a possible cutoff suffix.
455  StringRef str = strArg->getString();
456  unsigned numX = 0;
457  unsigned n = str.size();
458 
459  // Take into account the suffix.
460  unsigned suffix = 0;
461  if (ArgSuffix.second >= 0) {
462  const Expr *suffixEx = CE->getArg((unsigned)ArgSuffix.second);
463  llvm::APSInt Result;
464  if (!suffixEx->EvaluateAsInt(Result, BR.getContext()))
465  return;
466  // FIXME: Issue a warning.
467  if (Result.isNegative())
468  return;
469  suffix = (unsigned) Result.getZExtValue();
470  n = (n > suffix) ? n - suffix : 0;
471  }
472 
473  for (unsigned i = 0; i < n; ++i)
474  if (str[i] == 'X') ++numX;
475 
476  if (numX >= 6)
477  return;
478 
479  // Issue a warning.
480  PathDiagnosticLocation CELoc =
481  PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
482  SmallString<512> buf;
483  llvm::raw_svector_ostream out(buf);
484  out << "Call to '" << Name << "' should have at least 6 'X's in the"
485  " format string to be secure (" << numX << " 'X'";
486  if (numX != 1)
487  out << 's';
488  out << " seen";
489  if (suffix) {
490  out << ", " << suffix << " character";
491  if (suffix > 1)
492  out << 's';
493  out << " used as a suffix";
494  }
495  out << ')';
496  BR.EmitBasicReport(AC->getDecl(), filter.checkName_mkstemp,
497  "Insecure temporary file creation", "Security",
498  out.str(), CELoc, strArg->getSourceRange());
499 }
500 
501 //===----------------------------------------------------------------------===//
502 // Check: Any use of 'strcpy' is insecure.
503 //
504 // CWE-119: Improper Restriction of Operations within
505 // the Bounds of a Memory Buffer
506 //===----------------------------------------------------------------------===//
507 void WalkAST::checkCall_strcpy(const CallExpr *CE, const FunctionDecl *FD) {
508  if (!filter.check_strcpy)
509  return;
510 
511  if (!checkCall_strCommon(CE, FD))
512  return;
513 
514  // Issue a warning.
515  PathDiagnosticLocation CELoc =
516  PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
517  BR.EmitBasicReport(AC->getDecl(), filter.checkName_strcpy,
518  "Potential insecure memory buffer bounds restriction in "
519  "call 'strcpy'",
520  "Security",
521  "Call to function 'strcpy' is insecure as it does not "
522  "provide bounding of the memory buffer. Replace "
523  "unbounded copy functions with analogous functions that "
524  "support length arguments such as 'strlcpy'. CWE-119.",
525  CELoc, CE->getCallee()->getSourceRange());
526 }
527 
528 //===----------------------------------------------------------------------===//
529 // Check: Any use of 'strcat' is insecure.
530 //
531 // CWE-119: Improper Restriction of Operations within
532 // the Bounds of a Memory Buffer
533 //===----------------------------------------------------------------------===//
534 void WalkAST::checkCall_strcat(const CallExpr *CE, const FunctionDecl *FD) {
535  if (!filter.check_strcpy)
536  return;
537 
538  if (!checkCall_strCommon(CE, FD))
539  return;
540 
541  // Issue a warning.
542  PathDiagnosticLocation CELoc =
543  PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
544  BR.EmitBasicReport(AC->getDecl(), filter.checkName_strcpy,
545  "Potential insecure memory buffer bounds restriction in "
546  "call 'strcat'",
547  "Security",
548  "Call to function 'strcat' is insecure as it does not "
549  "provide bounding of the memory buffer. Replace "
550  "unbounded copy functions with analogous functions that "
551  "support length arguments such as 'strlcat'. CWE-119.",
552  CELoc, CE->getCallee()->getSourceRange());
553 }
554 
555 //===----------------------------------------------------------------------===//
556 // Common check for str* functions with no bounds parameters.
557 //===----------------------------------------------------------------------===//
558 bool WalkAST::checkCall_strCommon(const CallExpr *CE, const FunctionDecl *FD) {
559  const FunctionProtoType *FPT = FD->getType()->getAs<FunctionProtoType>();
560  if (!FPT)
561  return false;
562 
563  // Verify the function takes two arguments, three in the _chk version.
564  int numArgs = FPT->getNumParams();
565  if (numArgs != 2 && numArgs != 3)
566  return false;
567 
568  // Verify the type for both arguments.
569  for (int i = 0; i < 2; i++) {
570  // Verify that the arguments are pointers.
571  const PointerType *PT = FPT->getParamType(i)->getAs<PointerType>();
572  if (!PT)
573  return false;
574 
575  // Verify that the argument is a 'char*'.
576  if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
577  return false;
578  }
579 
580  return true;
581 }
582 
583 //===----------------------------------------------------------------------===//
584 // Check: Linear congruent random number generators should not be used
585 // Originally: <rdar://problem/63371000>
586 // CWE-338: Use of cryptographically weak prng
587 //===----------------------------------------------------------------------===//
588 
589 void WalkAST::checkCall_rand(const CallExpr *CE, const FunctionDecl *FD) {
590  if (!filter.check_rand || !CheckRand)
591  return;
592 
593  const FunctionProtoType *FTP = FD->getType()->getAs<FunctionProtoType>();
594  if (!FTP)
595  return;
596 
597  if (FTP->getNumParams() == 1) {
598  // Is the argument an 'unsigned short *'?
599  // (Actually any integer type is allowed.)
600  const PointerType *PT = FTP->getParamType(0)->getAs<PointerType>();
601  if (!PT)
602  return;
603 
605  return;
606  } else if (FTP->getNumParams() != 0)
607  return;
608 
609  // Issue a warning.
610  SmallString<256> buf1;
611  llvm::raw_svector_ostream os1(buf1);
612  os1 << '\'' << *FD << "' is a poor random number generator";
613 
614  SmallString<256> buf2;
615  llvm::raw_svector_ostream os2(buf2);
616  os2 << "Function '" << *FD
617  << "' is obsolete because it implements a poor random number generator."
618  << " Use 'arc4random' instead";
619 
620  PathDiagnosticLocation CELoc =
621  PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
622  BR.EmitBasicReport(AC->getDecl(), filter.checkName_rand, os1.str(),
623  "Security", os2.str(), CELoc,
624  CE->getCallee()->getSourceRange());
625 }
626 
627 //===----------------------------------------------------------------------===//
628 // Check: 'random' should not be used
629 // Originally: <rdar://problem/63371000>
630 //===----------------------------------------------------------------------===//
631 
632 void WalkAST::checkCall_random(const CallExpr *CE, const FunctionDecl *FD) {
633  if (!CheckRand || !filter.check_rand)
634  return;
635 
636  const FunctionProtoType *FTP = FD->getType()->getAs<FunctionProtoType>();
637  if (!FTP)
638  return;
639 
640  // Verify that the function takes no argument.
641  if (FTP->getNumParams() != 0)
642  return;
643 
644  // Issue a warning.
645  PathDiagnosticLocation CELoc =
646  PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
647  BR.EmitBasicReport(AC->getDecl(), filter.checkName_rand,
648  "'random' is not a secure random number generator",
649  "Security",
650  "The 'random' function produces a sequence of values that "
651  "an adversary may be able to predict. Use 'arc4random' "
652  "instead", CELoc, CE->getCallee()->getSourceRange());
653 }
654 
655 //===----------------------------------------------------------------------===//
656 // Check: 'vfork' should not be used.
657 // POS33-C: Do not use vfork().
658 //===----------------------------------------------------------------------===//
659 
660 void WalkAST::checkCall_vfork(const CallExpr *CE, const FunctionDecl *FD) {
661  if (!filter.check_vfork)
662  return;
663 
664  // All calls to vfork() are insecure, issue a warning.
665  PathDiagnosticLocation CELoc =
666  PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
667  BR.EmitBasicReport(AC->getDecl(), filter.checkName_vfork,
668  "Potential insecure implementation-specific behavior in "
669  "call 'vfork'",
670  "Security",
671  "Call to function 'vfork' is insecure as it can lead to "
672  "denial of service situations in the parent process. "
673  "Replace calls to vfork with calls to the safer "
674  "'posix_spawn' function",
675  CELoc, CE->getCallee()->getSourceRange());
676 }
677 
678 //===----------------------------------------------------------------------===//
679 // Check: Should check whether privileges are dropped successfully.
680 // Originally: <rdar://problem/6337132>
681 //===----------------------------------------------------------------------===//
682 
683 void WalkAST::checkUncheckedReturnValue(CallExpr *CE) {
684  if (!filter.check_UncheckedReturn)
685  return;
686 
687  const FunctionDecl *FD = CE->getDirectCallee();
688  if (!FD)
689  return;
690 
691  if (II_setid[0] == nullptr) {
692  static const char * const identifiers[num_setids] = {
693  "setuid", "setgid", "seteuid", "setegid",
694  "setreuid", "setregid"
695  };
696 
697  for (size_t i = 0; i < num_setids; i++)
698  II_setid[i] = &BR.getContext().Idents.get(identifiers[i]);
699  }
700 
701  const IdentifierInfo *id = FD->getIdentifier();
702  size_t identifierid;
703 
704  for (identifierid = 0; identifierid < num_setids; identifierid++)
705  if (id == II_setid[identifierid])
706  break;
707 
708  if (identifierid >= num_setids)
709  return;
710 
711  const FunctionProtoType *FTP = FD->getType()->getAs<FunctionProtoType>();
712  if (!FTP)
713  return;
714 
715  // Verify that the function takes one or two arguments (depending on
716  // the function).
717  if (FTP->getNumParams() != (identifierid < 4 ? 1 : 2))
718  return;
719 
720  // The arguments must be integers.
721  for (unsigned i = 0; i < FTP->getNumParams(); i++)
723  return;
724 
725  // Issue a warning.
726  SmallString<256> buf1;
727  llvm::raw_svector_ostream os1(buf1);
728  os1 << "Return value is not checked in call to '" << *FD << '\'';
729 
730  SmallString<256> buf2;
731  llvm::raw_svector_ostream os2(buf2);
732  os2 << "The return value from the call to '" << *FD
733  << "' is not checked. If an error occurs in '" << *FD
734  << "', the following code may execute with unexpected privileges";
735 
736  PathDiagnosticLocation CELoc =
737  PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
738  BR.EmitBasicReport(AC->getDecl(), filter.checkName_UncheckedReturn, os1.str(),
739  "Security", os2.str(), CELoc,
740  CE->getCallee()->getSourceRange());
741 }
742 
743 //===----------------------------------------------------------------------===//
744 // SecuritySyntaxChecker
745 //===----------------------------------------------------------------------===//
746 
747 namespace {
748 class SecuritySyntaxChecker : public Checker<check::ASTCodeBody> {
749 public:
750  ChecksFilter filter;
751 
752  void checkASTCodeBody(const Decl *D, AnalysisManager& mgr,
753  BugReporter &BR) const {
754  WalkAST walker(BR, mgr.getAnalysisDeclContext(D), filter);
755  walker.Visit(D->getBody());
756  }
757 };
758 }
759 
760 #define REGISTER_CHECKER(name) \
761  void ento::register##name(CheckerManager &mgr) { \
762  SecuritySyntaxChecker *checker = \
763  mgr.registerChecker<SecuritySyntaxChecker>(); \
764  checker->filter.check_##name = true; \
765  checker->filter.checkName_##name = mgr.getCurrentCheckName(); \
766  }
767 
768 REGISTER_CHECKER(gets)
769 REGISTER_CHECKER(getpw)
770 REGISTER_CHECKER(mkstemp)
771 REGISTER_CHECKER(mktemp)
772 REGISTER_CHECKER(strcpy)
773 REGISTER_CHECKER(rand)
774 REGISTER_CHECKER(vfork)
775 REGISTER_CHECKER(FloatLoopCounter)
776 REGISTER_CHECKER(UncheckedReturn)
777 
778 
Expr * getInc()
Definition: Stmt.h:1187
FunctionDecl - An instance of this class is created to represent a function declaration or definition...
Definition: Decl.h:1561
const internal::VariadicDynCastAllOfMatcher< Stmt, Expr > expr
Matches expressions.
Definition: ASTMatchers.h:1367
PointerType - C99 6.7.5.1 - Pointer Declarators.
Definition: Type.h:2179
Expr * getArg(unsigned Arg)
getArg - Return the specified argument.
Definition: Expr.h:2217
IdentifierInfo * getIdentifier() const
getIdentifier - Get the identifier that names this declaration, if there is one.
Definition: Decl.h:232
A helper class which wraps a boolean value set to false by default.
Definition: Checker.h:556
VarDecl - An instance of this class is created to represent a variable declaration or definition...
Definition: Decl.h:768
const Expr * getCallee() const
Definition: Expr.h:2188
unsigned getNumParams() const
Definition: Type.h:3271
One of these records is kept for each identifier that is lexed.
class LLVM_ALIGNAS(8) DependentTemplateSpecializationType const IdentifierInfo * Name
Represents a template specialization type whose template cannot be resolved, e.g. ...
Definition: Type.h:4549
Holds long-lived AST nodes (such as types and decls) that can be referred to throughout the semantic ...
Definition: ASTContext.h:92
AnalysisDeclContext contains the context data for the function or method under analysis.
Expr * getLHS() const
Definition: Expr.h:2943
static bool isRelationalOp(Opcode Opc)
Definition: Expr.h:2983
bool isIntegralOrUnscopedEnumerationType() const
Determine whether this type is an integral or unscoped enumeration type.
Definition: Type.cpp:1639
ForStmt - This represents a 'for (init;cond;inc)' stmt.
Definition: Stmt.h:1153
static bool isEqualityOp(Opcode Opc)
Definition: Expr.h:2986
const TargetInfo & getTargetInfo() const
Definition: ASTContext.h:588
A builtin binary operation expression such as "x + y" or "x <= y".
Definition: Expr.h:2897
Expr * IgnoreParenCasts() LLVM_READONLY
IgnoreParenCasts - Ignore parentheses and casts.
Definition: Expr.cpp:2326
Expr * getCond()
Definition: Stmt.h:1186
child_range children()
Definition: Stmt.h:637
QualType getType() const
Definition: Decl.h:599
AnalysisDeclContext * getAnalysisDeclContext(const Decl *D)
CompoundStmt - This represents a group of statements like { stmt stmt }.
Definition: Stmt.h:551
QualType getParamType(unsigned i) const
Definition: Type.h:3272
Represents a prototype with parameter type info, e.g.
Definition: Type.h:3073
bool isRealFloatingType() const
Floating point categories.
Definition: Type.cpp:1799
Expr - This represents one expression.
Definition: Expr.h:105
StringRef getName() const
Return the actual identifier string.
bool EvaluateAsInt(llvm::APSInt &Result, const ASTContext &Ctx, SideEffectsKind AllowSideEffects=SE_NoSideEffects) const
EvaluateAsInt - Return true if this is a constant which we can fold and convert to an integer...
UnaryOperator - This represents the unary-expression's (except sizeof and alignof), the postinc/postdec operators from postfix-expression, and various extensions.
Definition: Expr.h:1668
ValueDecl * getDecl()
Definition: Expr.h:1017
The result type of a method or function.
BugReporter is a utility class for generating PathDiagnostics for analysis.
Definition: BugReporter.h:388
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)
StmtVisitor - This class implements a simple visitor for Stmt subclasses.
Definition: StmtVisitor.h:178
#define REGISTER_CHECKER(name)
unsigned getCharByteWidth() const
Definition: Expr.h:1548
QualType getPointeeType() const
Definition: Type.h:2193
QualType getType() const
Definition: Expr.h:126
FunctionDecl * getDirectCallee()
If the callee is a FunctionDecl, return it. Otherwise return 0.
Definition: Expr.cpp:1209
StringRef getString() const
Definition: Expr.h:1514
const llvm::Triple & getTriple() const
Returns the target triple of the primary target.
unsigned getNumArgs() const
getNumArgs - Return the number of actual arguments to this call.
Definition: Expr.h:2205
Expr * IgnoreParenImpCasts() LLVM_READONLY
IgnoreParenImpCasts - Ignore parentheses and implicit casts.
Definition: Expr.cpp:2413
const T * getAs() const
Member-template getAs<specific type>'.
Definition: Type.h:5818
Expr * IgnoreParenLValueCasts() LLVM_READONLY
Ignore parentheses and lvalue casts.
Definition: Expr.cpp:2373
QualType getUnqualifiedType() const
Retrieve the unqualified variant of the given type, removing as little sugar as possible.
Definition: Type.h:5339
StringLiteral - This represents a string literal expression, e.g.
Definition: Expr.h:1466
Defines the clang::TargetInfo interface.
CallExpr - Represents a function call (C99 6.5.2.2, C++ [expr.call]).
Definition: Expr.h:2148
Expr * getRHS() const
Definition: Expr.h:2945
A reference to a declared variable, function, enum, etc.
Definition: Expr.h:932
static bool isArc4RandomAvailable(const ASTContext &Ctx)
NamedDecl - This represents a decl with a name.
Definition: Decl.h:213