CheckSecuritySyntaxOnly.cpp revision fa8277c52afa18430407f4a0a6d9878b1cce146a 
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"
16#include "clang/Analysis/AnalysisContext.h"
17#include "clang/Basic/TargetInfo.h"
18#include "clang/StaticAnalyzer/Core/BugReporter/BugReporter.h"
19#include "clang/StaticAnalyzer/Core/Checker.h"
20#include "clang/StaticAnalyzer/Core/PathSensitive/AnalysisManager.h"
21#include "llvm/ADT/SmallString.h"
22#include "llvm/ADT/StringSwitch.h"
23#include "llvm/Support/raw_ostream.h"
24
25using namespace clang;
26using namespace ento;
27
28static 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::FreeBSD ||
32         T.getOS() == llvm::Triple::NetBSD ||
33         T.getOS() == llvm::Triple::OpenBSD ||
34         T.getOS() == llvm::Triple::Bitrig ||
35         T.getOS() == llvm::Triple::DragonFly;
36}
37
38namespace {
39struct ChecksFilter {
40  DefaultBool check_gets;
41  DefaultBool check_getpw;
42  DefaultBool check_mktemp;
43  DefaultBool check_mkstemp;
44  DefaultBool check_strcpy;
45  DefaultBool check_rand;
46  DefaultBool check_vfork;
47  DefaultBool check_FloatLoopCounter;
48  DefaultBool check_UncheckedReturn;
49};
50
51class WalkAST : public StmtVisitor<WalkAST> {
52  BugReporter &BR;
53  AnalysisDeclContext* AC;
54  enum { num_setids = 6 };
55  IdentifierInfo *II_setid[num_setids];
56
57  const bool CheckRand;
58  const ChecksFilter &filter;
59
60public:
61  WalkAST(BugReporter &br, AnalysisDeclContext* ac,
62          const ChecksFilter &f)
63  : BR(br), AC(ac), II_setid(),
64    CheckRand(isArc4RandomAvailable(BR.getContext())),
65    filter(f) {}
66
67  // Statement visitor methods.
68  void VisitCallExpr(CallExpr *CE);
69  void VisitForStmt(ForStmt *S);
70  void VisitCompoundStmt (CompoundStmt *S);
71  void VisitStmt(Stmt *S) { VisitChildren(S); }
72
73  void VisitChildren(Stmt *S);
74
75  // Helpers.
76  bool checkCall_strCommon(const CallExpr *CE, const FunctionDecl *FD);
77
78  typedef void (WalkAST::*FnCheck)(const CallExpr *,
79				   const FunctionDecl *);
80
81  // Checker-specific methods.
82  void checkLoopConditionForFloat(const ForStmt *FS);
83  void checkCall_gets(const CallExpr *CE, const FunctionDecl *FD);
84  void checkCall_getpw(const CallExpr *CE, const FunctionDecl *FD);
85  void checkCall_mktemp(const CallExpr *CE, const FunctionDecl *FD);
86  void checkCall_mkstemp(const CallExpr *CE, const FunctionDecl *FD);
87  void checkCall_strcpy(const CallExpr *CE, const FunctionDecl *FD);
88  void checkCall_strcat(const CallExpr *CE, const FunctionDecl *FD);
89  void checkCall_rand(const CallExpr *CE, const FunctionDecl *FD);
90  void checkCall_random(const CallExpr *CE, const FunctionDecl *FD);
91  void checkCall_vfork(const CallExpr *CE, const FunctionDecl *FD);
92  void checkUncheckedReturnValue(CallExpr *CE);
93};
94} // end anonymous namespace
95
96//===----------------------------------------------------------------------===//
97// AST walking.
98//===----------------------------------------------------------------------===//
99
100void WalkAST::VisitChildren(Stmt *S) {
101  for (Stmt::child_iterator I = S->child_begin(), E = S->child_end(); I!=E; ++I)
102    if (Stmt *child = *I)
103      Visit(child);
104}
105
106void WalkAST::VisitCallExpr(CallExpr *CE) {
107  // Get the callee.
108  const FunctionDecl *FD = CE->getDirectCallee();
109
110  if (!FD)
111    return;
112
113  // Get the name of the callee. If it's a builtin, strip off the prefix.
114  IdentifierInfo *II = FD->getIdentifier();
115  if (!II)   // if no identifier, not a simple C function
116    return;
117  StringRef Name = II->getName();
118  if (Name.startswith("__builtin_"))
119    Name = Name.substr(10);
120
121  // Set the evaluation function by switching on the callee name.
122  FnCheck evalFunction = llvm::StringSwitch<FnCheck>(Name)
123    .Case("gets", &WalkAST::checkCall_gets)
124    .Case("getpw", &WalkAST::checkCall_getpw)
125    .Case("mktemp", &WalkAST::checkCall_mktemp)
126    .Case("mkstemp", &WalkAST::checkCall_mkstemp)
127    .Case("mkdtemp", &WalkAST::checkCall_mkstemp)
128    .Case("mkstemps", &WalkAST::checkCall_mkstemp)
129    .Cases("strcpy", "__strcpy_chk", &WalkAST::checkCall_strcpy)
130    .Cases("strcat", "__strcat_chk", &WalkAST::checkCall_strcat)
131    .Case("drand48", &WalkAST::checkCall_rand)
132    .Case("erand48", &WalkAST::checkCall_rand)
133    .Case("jrand48", &WalkAST::checkCall_rand)
134    .Case("lrand48", &WalkAST::checkCall_rand)
135    .Case("mrand48", &WalkAST::checkCall_rand)
136    .Case("nrand48", &WalkAST::checkCall_rand)
137    .Case("lcong48", &WalkAST::checkCall_rand)
138    .Case("rand", &WalkAST::checkCall_rand)
139    .Case("rand_r", &WalkAST::checkCall_rand)
140    .Case("random", &WalkAST::checkCall_random)
141    .Case("vfork", &WalkAST::checkCall_vfork)
142    .Default(NULL);
143
144  // If the callee isn't defined, it is not of security concern.
145  // Check and evaluate the call.
146  if (evalFunction)
147    (this->*evalFunction)(CE, FD);
148
149  // Recurse and check children.
150  VisitChildren(CE);
151}
152
153void WalkAST::VisitCompoundStmt(CompoundStmt *S) {
154  for (Stmt::child_iterator I = S->child_begin(), E = S->child_end(); I!=E; ++I)
155    if (Stmt *child = *I) {
156      if (CallExpr *CE = dyn_cast<CallExpr>(child))
157        checkUncheckedReturnValue(CE);
158      Visit(child);
159    }
160}
161
162void WalkAST::VisitForStmt(ForStmt *FS) {
163  checkLoopConditionForFloat(FS);
164
165  // Recurse and check children.
166  VisitChildren(FS);
167}
168
169//===----------------------------------------------------------------------===//
170// Check: floating poing variable used as loop counter.
171// Originally: <rdar://problem/6336718>
172// Implements: CERT security coding advisory FLP-30.
173//===----------------------------------------------------------------------===//
174
175static const DeclRefExpr*
176getIncrementedVar(const Expr *expr, const VarDecl *x, const VarDecl *y) {
177  expr = expr->IgnoreParenCasts();
178
179  if (const BinaryOperator *B = dyn_cast<BinaryOperator>(expr)) {
180    if (!(B->isAssignmentOp() || B->isCompoundAssignmentOp() ||
181          B->getOpcode() == BO_Comma))
182      return NULL;
183
184    if (const DeclRefExpr *lhs = getIncrementedVar(B->getLHS(), x, y))
185      return lhs;
186
187    if (const DeclRefExpr *rhs = getIncrementedVar(B->getRHS(), x, y))
188      return rhs;
189
190    return NULL;
191  }
192
193  if (const DeclRefExpr *DR = dyn_cast<DeclRefExpr>(expr)) {
194    const NamedDecl *ND = DR->getDecl();
195    return ND == x || ND == y ? DR : NULL;
196  }
197
198  if (const UnaryOperator *U = dyn_cast<UnaryOperator>(expr))
199    return U->isIncrementDecrementOp()
200      ? getIncrementedVar(U->getSubExpr(), x, y) : NULL;
201
202  return NULL;
203}
204
205/// CheckLoopConditionForFloat - This check looks for 'for' statements that
206///  use a floating point variable as a loop counter.
207///  CERT: FLP30-C, FLP30-CPP.
208///
209void WalkAST::checkLoopConditionForFloat(const ForStmt *FS) {
210  if (!filter.check_FloatLoopCounter)
211    return;
212
213  // Does the loop have a condition?
214  const Expr *condition = FS->getCond();
215
216  if (!condition)
217    return;
218
219  // Does the loop have an increment?
220  const Expr *increment = FS->getInc();
221
222  if (!increment)
223    return;
224
225  // Strip away '()' and casts.
226  condition = condition->IgnoreParenCasts();
227  increment = increment->IgnoreParenCasts();
228
229  // Is the loop condition a comparison?
230  const BinaryOperator *B = dyn_cast<BinaryOperator>(condition);
231
232  if (!B)
233    return;
234
235  // Is this a comparison?
236  if (!(B->isRelationalOp() || B->isEqualityOp()))
237    return;
238
239  // Are we comparing variables?
240  const DeclRefExpr *drLHS =
241    dyn_cast<DeclRefExpr>(B->getLHS()->IgnoreParenLValueCasts());
242  const DeclRefExpr *drRHS =
243    dyn_cast<DeclRefExpr>(B->getRHS()->IgnoreParenLValueCasts());
244
245  // Does at least one of the variables have a floating point type?
246  drLHS = drLHS && drLHS->getType()->isRealFloatingType() ? drLHS : NULL;
247  drRHS = drRHS && drRHS->getType()->isRealFloatingType() ? drRHS : NULL;
248
249  if (!drLHS && !drRHS)
250    return;
251
252  const VarDecl *vdLHS = drLHS ? dyn_cast<VarDecl>(drLHS->getDecl()) : NULL;
253  const VarDecl *vdRHS = drRHS ? dyn_cast<VarDecl>(drRHS->getDecl()) : NULL;
254
255  if (!vdLHS && !vdRHS)
256    return;
257
258  // Does either variable appear in increment?
259  const DeclRefExpr *drInc = getIncrementedVar(increment, vdLHS, vdRHS);
260
261  if (!drInc)
262    return;
263
264  // Emit the error.  First figure out which DeclRefExpr in the condition
265  // referenced the compared variable.
266  assert(drInc->getDecl());
267  const DeclRefExpr *drCond = vdLHS == drInc->getDecl() ? drLHS : drRHS;
268
269  SmallVector<SourceRange, 2> ranges;
270  SmallString<256> sbuf;
271  llvm::raw_svector_ostream os(sbuf);
272
273  os << "Variable '" << drCond->getDecl()->getName()
274     << "' with floating point type '" << drCond->getType().getAsString()
275     << "' should not be used as a loop counter";
276
277  ranges.push_back(drCond->getSourceRange());
278  ranges.push_back(drInc->getSourceRange());
279
280  const char *bugType = "Floating point variable used as loop counter";
281
282  PathDiagnosticLocation FSLoc =
283    PathDiagnosticLocation::createBegin(FS, BR.getSourceManager(), AC);
284  BR.EmitBasicReport(AC->getDecl(),
285                     bugType, "Security", os.str(),
286                     FSLoc, ranges.data(), ranges.size());
287}
288
289//===----------------------------------------------------------------------===//
290// Check: Any use of 'gets' is insecure.
291// Originally: <rdar://problem/6335715>
292// Implements (part of): 300-BSI (buildsecurityin.us-cert.gov)
293// CWE-242: Use of Inherently Dangerous Function
294//===----------------------------------------------------------------------===//
295
296void WalkAST::checkCall_gets(const CallExpr *CE, const FunctionDecl *FD) {
297  if (!filter.check_gets)
298    return;
299
300  const FunctionProtoType *FPT = FD->getType()->getAs<FunctionProtoType>();
301  if (!FPT)
302    return;
303
304  // Verify that the function takes a single argument.
305  if (FPT->getNumArgs() != 1)
306    return;
307
308  // Is the argument a 'char*'?
309  const PointerType *PT = FPT->getArgType(0)->getAs<PointerType>();
310  if (!PT)
311    return;
312
313  if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
314    return;
315
316  // Issue a warning.
317  SourceRange R = CE->getCallee()->getSourceRange();
318  PathDiagnosticLocation CELoc =
319    PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
320  BR.EmitBasicReport(AC->getDecl(),
321                     "Potential buffer overflow in call to 'gets'",
322                     "Security",
323                     "Call to function 'gets' is extremely insecure as it can "
324                     "always result in a buffer overflow",
325                     CELoc, &R, 1);
326}
327
328//===----------------------------------------------------------------------===//
329// Check: Any use of 'getpwd' is insecure.
330// CWE-477: Use of Obsolete Functions
331//===----------------------------------------------------------------------===//
332
333void WalkAST::checkCall_getpw(const CallExpr *CE, const FunctionDecl *FD) {
334  if (!filter.check_getpw)
335    return;
336
337  const FunctionProtoType *FPT = FD->getType()->getAs<FunctionProtoType>();
338  if (!FPT)
339    return;
340
341  // Verify that the function takes two arguments.
342  if (FPT->getNumArgs() != 2)
343    return;
344
345  // Verify the first argument type is integer.
346  if (!FPT->getArgType(0)->isIntegralOrUnscopedEnumerationType())
347    return;
348
349  // Verify the second argument type is char*.
350  const PointerType *PT = FPT->getArgType(1)->getAs<PointerType>();
351  if (!PT)
352    return;
353
354  if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
355    return;
356
357  // Issue a warning.
358  SourceRange R = CE->getCallee()->getSourceRange();
359  PathDiagnosticLocation CELoc =
360    PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
361  BR.EmitBasicReport(AC->getDecl(),
362                     "Potential buffer overflow in call to 'getpw'",
363                     "Security",
364                     "The getpw() function is dangerous as it may overflow the "
365                     "provided buffer. It is obsoleted by getpwuid().",
366                     CELoc, &R, 1);
367}
368
369//===----------------------------------------------------------------------===//
370// Check: Any use of 'mktemp' is insecure.  It is obsoleted by mkstemp().
371// CWE-377: Insecure Temporary File
372//===----------------------------------------------------------------------===//
373
374void WalkAST::checkCall_mktemp(const CallExpr *CE, const FunctionDecl *FD) {
375  if (!filter.check_mktemp) {
376    // Fall back to the security check of looking for enough 'X's in the
377    // format string, since that is a less severe warning.
378    checkCall_mkstemp(CE, FD);
379    return;
380  }
381
382  const FunctionProtoType *FPT = FD->getType()->getAs<FunctionProtoType>();
383  if(!FPT)
384    return;
385
386  // Verify that the function takes a single argument.
387  if (FPT->getNumArgs() != 1)
388    return;
389
390  // Verify that the argument is Pointer Type.
391  const PointerType *PT = FPT->getArgType(0)->getAs<PointerType>();
392  if (!PT)
393    return;
394
395  // Verify that the argument is a 'char*'.
396  if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
397    return;
398
399  // Issue a waring.
400  SourceRange R = CE->getCallee()->getSourceRange();
401  PathDiagnosticLocation CELoc =
402    PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
403  BR.EmitBasicReport(AC->getDecl(),
404                     "Potential insecure temporary file in call 'mktemp'",
405                     "Security",
406                     "Call to function 'mktemp' is insecure as it always "
407                     "creates or uses insecure temporary file.  Use 'mkstemp' "
408                     "instead",
409                     CELoc, &R, 1);
410}
411
412
413//===----------------------------------------------------------------------===//
414// Check: Use of 'mkstemp', 'mktemp', 'mkdtemp' should contain at least 6 X's.
415//===----------------------------------------------------------------------===//
416
417void WalkAST::checkCall_mkstemp(const CallExpr *CE, const FunctionDecl *FD) {
418  if (!filter.check_mkstemp)
419    return;
420
421  StringRef Name = FD->getIdentifier()->getName();
422  std::pair<signed, signed> ArgSuffix =
423    llvm::StringSwitch<std::pair<signed, signed> >(Name)
424      .Case("mktemp", std::make_pair(0,-1))
425      .Case("mkstemp", std::make_pair(0,-1))
426      .Case("mkdtemp", std::make_pair(0,-1))
427      .Case("mkstemps", std::make_pair(0,1))
428      .Default(std::make_pair(-1, -1));
429
430  assert(ArgSuffix.first >= 0 && "Unsupported function");
431
432  // Check if the number of arguments is consistent with out expectations.
433  unsigned numArgs = CE->getNumArgs();
434  if ((signed) numArgs <= ArgSuffix.first)
435    return;
436
437  const StringLiteral *strArg =
438    dyn_cast<StringLiteral>(CE->getArg((unsigned)ArgSuffix.first)
439                              ->IgnoreParenImpCasts());
440
441  // Currently we only handle string literals.  It is possible to do better,
442  // either by looking at references to const variables, or by doing real
443  // flow analysis.
444  if (!strArg || strArg->getCharByteWidth() != 1)
445    return;
446
447  // Count the number of X's, taking into account a possible cutoff suffix.
448  StringRef str = strArg->getString();
449  unsigned numX = 0;
450  unsigned n = str.size();
451
452  // Take into account the suffix.
453  unsigned suffix = 0;
454  if (ArgSuffix.second >= 0) {
455    const Expr *suffixEx = CE->getArg((unsigned)ArgSuffix.second);
456    llvm::APSInt Result;
457    if (!suffixEx->EvaluateAsInt(Result, BR.getContext()))
458      return;
459    // FIXME: Issue a warning.
460    if (Result.isNegative())
461      return;
462    suffix = (unsigned) Result.getZExtValue();
463    n = (n > suffix) ? n - suffix : 0;
464  }
465
466  for (unsigned i = 0; i < n; ++i)
467    if (str[i] == 'X') ++numX;
468
469  if (numX >= 6)
470    return;
471
472  // Issue a warning.
473  SourceRange R = strArg->getSourceRange();
474  PathDiagnosticLocation CELoc =
475    PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
476  SmallString<512> buf;
477  llvm::raw_svector_ostream out(buf);
478  out << "Call to '" << Name << "' should have at least 6 'X's in the"
479    " format string to be secure (" << numX << " 'X'";
480  if (numX != 1)
481    out << 's';
482  out << " seen";
483  if (suffix) {
484    out << ", " << suffix << " character";
485    if (suffix > 1)
486      out << 's';
487    out << " used as a suffix";
488  }
489  out << ')';
490  BR.EmitBasicReport(AC->getDecl(),
491                     "Insecure temporary file creation", "Security",
492                     out.str(), CELoc, &R, 1);
493}
494
495//===----------------------------------------------------------------------===//
496// Check: Any use of 'strcpy' is insecure.
497//
498// CWE-119: Improper Restriction of Operations within
499// the Bounds of a Memory Buffer
500//===----------------------------------------------------------------------===//
501void WalkAST::checkCall_strcpy(const CallExpr *CE, const FunctionDecl *FD) {
502  if (!filter.check_strcpy)
503    return;
504
505  if (!checkCall_strCommon(CE, FD))
506    return;
507
508  // Issue a warning.
509  SourceRange R = CE->getCallee()->getSourceRange();
510  PathDiagnosticLocation CELoc =
511    PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
512  BR.EmitBasicReport(AC->getDecl(),
513                     "Potential insecure memory buffer bounds restriction in "
514                     "call 'strcpy'",
515                     "Security",
516                     "Call to function 'strcpy' is insecure as it does not "
517                     "provide bounding of the memory buffer. Replace "
518                     "unbounded copy functions with analogous functions that "
519                     "support length arguments such as 'strlcpy'. CWE-119.",
520                     CELoc, &R, 1);
521}
522
523//===----------------------------------------------------------------------===//
524// Check: Any use of 'strcat' is insecure.
525//
526// CWE-119: Improper Restriction of Operations within
527// the Bounds of a Memory Buffer
528//===----------------------------------------------------------------------===//
529void WalkAST::checkCall_strcat(const CallExpr *CE, const FunctionDecl *FD) {
530  if (!filter.check_strcpy)
531    return;
532
533  if (!checkCall_strCommon(CE, FD))
534    return;
535
536  // Issue a warning.
537  SourceRange R = CE->getCallee()->getSourceRange();
538  PathDiagnosticLocation CELoc =
539    PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
540  BR.EmitBasicReport(AC->getDecl(),
541                     "Potential insecure memory buffer bounds restriction in "
542                     "call 'strcat'",
543                     "Security",
544                     "Call to function 'strcat' is insecure as it does not "
545                     "provide bounding of the memory buffer. Replace "
546                     "unbounded copy functions with analogous functions that "
547                     "support length arguments such as 'strlcat'. CWE-119.",
548                     CELoc, &R, 1);
549}
550
551//===----------------------------------------------------------------------===//
552// Common check for str* functions with no bounds parameters.
553//===----------------------------------------------------------------------===//
554bool WalkAST::checkCall_strCommon(const CallExpr *CE, const FunctionDecl *FD) {
555  const FunctionProtoType *FPT = FD->getType()->getAs<FunctionProtoType>();
556  if (!FPT)
557    return false;
558
559  // Verify the function takes two arguments, three in the _chk version.
560  int numArgs = FPT->getNumArgs();
561  if (numArgs != 2 && numArgs != 3)
562    return false;
563
564  // Verify the type for both arguments.
565  for (int i = 0; i < 2; i++) {
566    // Verify that the arguments are pointers.
567    const PointerType *PT = FPT->getArgType(i)->getAs<PointerType>();
568    if (!PT)
569      return false;
570
571    // Verify that the argument is a 'char*'.
572    if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
573      return false;
574  }
575
576  return true;
577}
578
579//===----------------------------------------------------------------------===//
580// Check: Linear congruent random number generators should not be used
581// Originally: <rdar://problem/63371000>
582// CWE-338: Use of cryptographically weak prng
583//===----------------------------------------------------------------------===//
584
585void WalkAST::checkCall_rand(const CallExpr *CE, const FunctionDecl *FD) {
586  if (!filter.check_rand || !CheckRand)
587    return;
588
589  const FunctionProtoType *FTP = FD->getType()->getAs<FunctionProtoType>();
590  if (!FTP)
591    return;
592
593  if (FTP->getNumArgs() == 1) {
594    // Is the argument an 'unsigned short *'?
595    // (Actually any integer type is allowed.)
596    const PointerType *PT = FTP->getArgType(0)->getAs<PointerType>();
597    if (!PT)
598      return;
599
600    if (! PT->getPointeeType()->isIntegralOrUnscopedEnumerationType())
601      return;
602  }
603  else if (FTP->getNumArgs() != 0)
604    return;
605
606  // Issue a warning.
607  SmallString<256> buf1;
608  llvm::raw_svector_ostream os1(buf1);
609  os1 << '\'' << *FD << "' is a poor random number generator";
610
611  SmallString<256> buf2;
612  llvm::raw_svector_ostream os2(buf2);
613  os2 << "Function '" << *FD
614      << "' is obsolete because it implements a poor random number generator."
615      << "  Use 'arc4random' instead";
616
617  SourceRange R = CE->getCallee()->getSourceRange();
618  PathDiagnosticLocation CELoc =
619    PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
620  BR.EmitBasicReport(AC->getDecl(), os1.str(), "Security", os2.str(),
621                     CELoc, &R, 1);
622}
623
624//===----------------------------------------------------------------------===//
625// Check: 'random' should not be used
626// Originally: <rdar://problem/63371000>
627//===----------------------------------------------------------------------===//
628
629void WalkAST::checkCall_random(const CallExpr *CE, const FunctionDecl *FD) {
630  if (!CheckRand || !filter.check_rand)
631    return;
632
633  const FunctionProtoType *FTP = FD->getType()->getAs<FunctionProtoType>();
634  if (!FTP)
635    return;
636
637  // Verify that the function takes no argument.
638  if (FTP->getNumArgs() != 0)
639    return;
640
641  // Issue a warning.
642  SourceRange R = CE->getCallee()->getSourceRange();
643  PathDiagnosticLocation CELoc =
644    PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
645  BR.EmitBasicReport(AC->getDecl(),
646                     "'random' is not a secure random number generator",
647                     "Security",
648                     "The 'random' function produces a sequence of values that "
649                     "an adversary may be able to predict.  Use 'arc4random' "
650                     "instead", CELoc, &R, 1);
651}
652
653//===----------------------------------------------------------------------===//
654// Check: 'vfork' should not be used.
655// POS33-C: Do not use vfork().
656//===----------------------------------------------------------------------===//
657
658void WalkAST::checkCall_vfork(const CallExpr *CE, const FunctionDecl *FD) {
659  if (!filter.check_vfork)
660    return;
661
662  // All calls to vfork() are insecure, issue a warning.
663  SourceRange R = CE->getCallee()->getSourceRange();
664  PathDiagnosticLocation CELoc =
665    PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
666  BR.EmitBasicReport(AC->getDecl(),
667                     "Potential insecure implementation-specific behavior in "
668                     "call 'vfork'",
669                     "Security",
670                     "Call to function 'vfork' is insecure as it can lead to "
671                     "denial of service situations in the parent process. "
672                     "Replace calls to vfork with calls to the safer "
673                     "'posix_spawn' function",
674                     CELoc, &R, 1);
675}
676
677//===----------------------------------------------------------------------===//
678// Check: Should check whether privileges are dropped successfully.
679// Originally: <rdar://problem/6337132>
680//===----------------------------------------------------------------------===//
681
682void WalkAST::checkUncheckedReturnValue(CallExpr *CE) {
683  if (!filter.check_UncheckedReturn)
684    return;
685
686  const FunctionDecl *FD = CE->getDirectCallee();
687  if (!FD)
688    return;
689
690  if (II_setid[0] == NULL) {
691    static const char * const identifiers[num_setids] = {
692      "setuid", "setgid", "seteuid", "setegid",
693      "setreuid", "setregid"
694    };
695
696    for (size_t i = 0; i < num_setids; i++)
697      II_setid[i] = &BR.getContext().Idents.get(identifiers[i]);
698  }
699
700  const IdentifierInfo *id = FD->getIdentifier();
701  size_t identifierid;
702
703  for (identifierid = 0; identifierid < num_setids; identifierid++)
704    if (id == II_setid[identifierid])
705      break;
706
707  if (identifierid >= num_setids)
708    return;
709
710  const FunctionProtoType *FTP = FD->getType()->getAs<FunctionProtoType>();
711  if (!FTP)
712    return;
713
714  // Verify that the function takes one or two arguments (depending on
715  //   the function).
716  if (FTP->getNumArgs() != (identifierid < 4 ? 1 : 2))
717    return;
718
719  // The arguments must be integers.
720  for (unsigned i = 0; i < FTP->getNumArgs(); i++)
721    if (! FTP->getArgType(i)->isIntegralOrUnscopedEnumerationType())
722      return;
723
724  // Issue a warning.
725  SmallString<256> buf1;
726  llvm::raw_svector_ostream os1(buf1);
727  os1 << "Return value is not checked in call to '" << *FD << '\'';
728
729  SmallString<256> buf2;
730  llvm::raw_svector_ostream os2(buf2);
731  os2 << "The return value from the call to '" << *FD
732      << "' is not checked.  If an error occurs in '" << *FD
733      << "', the following code may execute with unexpected privileges";
734
735  SourceRange R = CE->getCallee()->getSourceRange();
736  PathDiagnosticLocation CELoc =
737    PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
738  BR.EmitBasicReport(AC->getDecl(), os1.str(), "Security", os2.str(),
739                     CELoc, &R, 1);
740}
741
742//===----------------------------------------------------------------------===//
743// SecuritySyntaxChecker
744//===----------------------------------------------------------------------===//
745
746namespace {
747class SecuritySyntaxChecker : public Checker<check::ASTCodeBody> {
748public:
749  ChecksFilter filter;
750
751  void checkASTCodeBody(const Decl *D, AnalysisManager& mgr,
752                        BugReporter &BR) const {
753    WalkAST walker(BR, mgr.getAnalysisDeclContext(D), filter);
754    walker.Visit(D->getBody());
755  }
756};
757}
758
759#define REGISTER_CHECKER(name) \
760void ento::register##name(CheckerManager &mgr) {\
761  mgr.registerChecker<SecuritySyntaxChecker>()->filter.check_##name = true;\
762}
763
764REGISTER_CHECKER(gets)
765REGISTER_CHECKER(getpw)
766REGISTER_CHECKER(mkstemp)
767REGISTER_CHECKER(mktemp)
768REGISTER_CHECKER(strcpy)
769REGISTER_CHECKER(rand)
770REGISTER_CHECKER(vfork)
771REGISTER_CHECKER(FloatLoopCounter)
772REGISTER_CHECKER(UncheckedReturn)
773
774
775