CheckSecuritySyntaxOnly.cpp revision f7ccbad5d9949e7ddd1cbef43d482553b811e026 
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/Analysis/AnalysisContext.h"
16#include "clang/AST/StmtVisitor.h"
17#include "clang/Basic/TargetInfo.h"
18#include "clang/StaticAnalyzer/Core/Checker.h"
19#include "clang/StaticAnalyzer/Core/BugReporter/BugReporter.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::DragonFly;
35}
36
37namespace {
38struct DefaultBool {
39  bool val;
40  DefaultBool() : val(false) {}
41  operator bool() const { return val; }
42  DefaultBool &operator=(bool b) { val = b; return *this; }
43};
44
45struct ChecksFilter {
46  DefaultBool check_gets;
47  DefaultBool check_getpw;
48  DefaultBool check_mktemp;
49  DefaultBool check_mkstemp;
50  DefaultBool check_strcpy;
51  DefaultBool check_rand;
52  DefaultBool check_vfork;
53  DefaultBool check_FloatLoopCounter;
54  DefaultBool check_UncheckedReturn;
55};
56
57class WalkAST : public StmtVisitor<WalkAST> {
58  BugReporter &BR;
59  AnalysisDeclContext* AC;
60  enum { num_setids = 6 };
61  IdentifierInfo *II_setid[num_setids];
62
63  const bool CheckRand;
64  const ChecksFilter &filter;
65
66public:
67  WalkAST(BugReporter &br, AnalysisDeclContext* ac,
68          const ChecksFilter &f)
69  : BR(br), AC(ac), II_setid(),
70    CheckRand(isArc4RandomAvailable(BR.getContext())),
71    filter(f) {}
72
73  // Statement visitor methods.
74  void VisitCallExpr(CallExpr *CE);
75  void VisitForStmt(ForStmt *S);
76  void VisitCompoundStmt (CompoundStmt *S);
77  void VisitStmt(Stmt *S) { VisitChildren(S); }
78
79  void VisitChildren(Stmt *S);
80
81  // Helpers.
82  bool checkCall_strCommon(const CallExpr *CE, const FunctionDecl *FD);
83
84  typedef void (WalkAST::*FnCheck)(const CallExpr *,
85				   const FunctionDecl *);
86
87  // Checker-specific methods.
88  void checkLoopConditionForFloat(const ForStmt *FS);
89  void checkCall_gets(const CallExpr *CE, const FunctionDecl *FD);
90  void checkCall_getpw(const CallExpr *CE, const FunctionDecl *FD);
91  void checkCall_mktemp(const CallExpr *CE, const FunctionDecl *FD);
92  void checkCall_mkstemp(const CallExpr *CE, const FunctionDecl *FD);
93  void checkCall_strcpy(const CallExpr *CE, const FunctionDecl *FD);
94  void checkCall_strcat(const CallExpr *CE, const FunctionDecl *FD);
95  void checkCall_rand(const CallExpr *CE, const FunctionDecl *FD);
96  void checkCall_random(const CallExpr *CE, const FunctionDecl *FD);
97  void checkCall_vfork(const CallExpr *CE, const FunctionDecl *FD);
98  void checkUncheckedReturnValue(CallExpr *CE);
99};
100} // end anonymous namespace
101
102//===----------------------------------------------------------------------===//
103// AST walking.
104//===----------------------------------------------------------------------===//
105
106void WalkAST::VisitChildren(Stmt *S) {
107  for (Stmt::child_iterator I = S->child_begin(), E = S->child_end(); I!=E; ++I)
108    if (Stmt *child = *I)
109      Visit(child);
110}
111
112void WalkAST::VisitCallExpr(CallExpr *CE) {
113  // Get the callee.
114  const FunctionDecl *FD = CE->getDirectCallee();
115
116  if (!FD)
117    return;
118
119  // Get the name of the callee. If it's a builtin, strip off the prefix.
120  IdentifierInfo *II = FD->getIdentifier();
121  if (!II)   // if no identifier, not a simple C function
122    return;
123  StringRef Name = II->getName();
124  if (Name.startswith("__builtin_"))
125    Name = Name.substr(10);
126
127  // Set the evaluation function by switching on the callee name.
128  FnCheck evalFunction = llvm::StringSwitch<FnCheck>(Name)
129    .Case("gets", &WalkAST::checkCall_gets)
130    .Case("getpw", &WalkAST::checkCall_getpw)
131    .Case("mktemp", &WalkAST::checkCall_mktemp)
132    .Case("mkstemp", &WalkAST::checkCall_mkstemp)
133    .Case("mkdtemp", &WalkAST::checkCall_mkstemp)
134    .Case("mkstemps", &WalkAST::checkCall_mkstemp)
135    .Cases("strcpy", "__strcpy_chk", &WalkAST::checkCall_strcpy)
136    .Cases("strcat", "__strcat_chk", &WalkAST::checkCall_strcat)
137    .Case("drand48", &WalkAST::checkCall_rand)
138    .Case("erand48", &WalkAST::checkCall_rand)
139    .Case("jrand48", &WalkAST::checkCall_rand)
140    .Case("lrand48", &WalkAST::checkCall_rand)
141    .Case("mrand48", &WalkAST::checkCall_rand)
142    .Case("nrand48", &WalkAST::checkCall_rand)
143    .Case("lcong48", &WalkAST::checkCall_rand)
144    .Case("rand", &WalkAST::checkCall_rand)
145    .Case("rand_r", &WalkAST::checkCall_rand)
146    .Case("random", &WalkAST::checkCall_random)
147    .Case("vfork", &WalkAST::checkCall_vfork)
148    .Default(NULL);
149
150  // If the callee isn't defined, it is not of security concern.
151  // Check and evaluate the call.
152  if (evalFunction)
153    (this->*evalFunction)(CE, FD);
154
155  // Recurse and check children.
156  VisitChildren(CE);
157}
158
159void WalkAST::VisitCompoundStmt(CompoundStmt *S) {
160  for (Stmt::child_iterator I = S->child_begin(), E = S->child_end(); I!=E; ++I)
161    if (Stmt *child = *I) {
162      if (CallExpr *CE = dyn_cast<CallExpr>(child))
163        checkUncheckedReturnValue(CE);
164      Visit(child);
165    }
166}
167
168void WalkAST::VisitForStmt(ForStmt *FS) {
169  checkLoopConditionForFloat(FS);
170
171  // Recurse and check children.
172  VisitChildren(FS);
173}
174
175//===----------------------------------------------------------------------===//
176// Check: floating poing variable used as loop counter.
177// Originally: <rdar://problem/6336718>
178// Implements: CERT security coding advisory FLP-30.
179//===----------------------------------------------------------------------===//
180
181static const DeclRefExpr*
182getIncrementedVar(const Expr *expr, const VarDecl *x, const VarDecl *y) {
183  expr = expr->IgnoreParenCasts();
184
185  if (const BinaryOperator *B = dyn_cast<BinaryOperator>(expr)) {
186    if (!(B->isAssignmentOp() || B->isCompoundAssignmentOp() ||
187          B->getOpcode() == BO_Comma))
188      return NULL;
189
190    if (const DeclRefExpr *lhs = getIncrementedVar(B->getLHS(), x, y))
191      return lhs;
192
193    if (const DeclRefExpr *rhs = getIncrementedVar(B->getRHS(), x, y))
194      return rhs;
195
196    return NULL;
197  }
198
199  if (const DeclRefExpr *DR = dyn_cast<DeclRefExpr>(expr)) {
200    const NamedDecl *ND = DR->getDecl();
201    return ND == x || ND == y ? DR : NULL;
202  }
203
204  if (const UnaryOperator *U = dyn_cast<UnaryOperator>(expr))
205    return U->isIncrementDecrementOp()
206      ? getIncrementedVar(U->getSubExpr(), x, y) : NULL;
207
208  return NULL;
209}
210
211/// CheckLoopConditionForFloat - This check looks for 'for' statements that
212///  use a floating point variable as a loop counter.
213///  CERT: FLP30-C, FLP30-CPP.
214///
215void WalkAST::checkLoopConditionForFloat(const ForStmt *FS) {
216  if (!filter.check_FloatLoopCounter)
217    return;
218
219  // Does the loop have a condition?
220  const Expr *condition = FS->getCond();
221
222  if (!condition)
223    return;
224
225  // Does the loop have an increment?
226  const Expr *increment = FS->getInc();
227
228  if (!increment)
229    return;
230
231  // Strip away '()' and casts.
232  condition = condition->IgnoreParenCasts();
233  increment = increment->IgnoreParenCasts();
234
235  // Is the loop condition a comparison?
236  const BinaryOperator *B = dyn_cast<BinaryOperator>(condition);
237
238  if (!B)
239    return;
240
241  // Is this a comparison?
242  if (!(B->isRelationalOp() || B->isEqualityOp()))
243    return;
244
245  // Are we comparing variables?
246  const DeclRefExpr *drLHS =
247    dyn_cast<DeclRefExpr>(B->getLHS()->IgnoreParenLValueCasts());
248  const DeclRefExpr *drRHS =
249    dyn_cast<DeclRefExpr>(B->getRHS()->IgnoreParenLValueCasts());
250
251  // Does at least one of the variables have a floating point type?
252  drLHS = drLHS && drLHS->getType()->isRealFloatingType() ? drLHS : NULL;
253  drRHS = drRHS && drRHS->getType()->isRealFloatingType() ? drRHS : NULL;
254
255  if (!drLHS && !drRHS)
256    return;
257
258  const VarDecl *vdLHS = drLHS ? dyn_cast<VarDecl>(drLHS->getDecl()) : NULL;
259  const VarDecl *vdRHS = drRHS ? dyn_cast<VarDecl>(drRHS->getDecl()) : NULL;
260
261  if (!vdLHS && !vdRHS)
262    return;
263
264  // Does either variable appear in increment?
265  const DeclRefExpr *drInc = getIncrementedVar(increment, vdLHS, vdRHS);
266
267  if (!drInc)
268    return;
269
270  // Emit the error.  First figure out which DeclRefExpr in the condition
271  // referenced the compared variable.
272  const DeclRefExpr *drCond = vdLHS == drInc->getDecl() ? drLHS : drRHS;
273
274  SmallVector<SourceRange, 2> ranges;
275  SmallString<256> sbuf;
276  llvm::raw_svector_ostream os(sbuf);
277
278  os << "Variable '" << drCond->getDecl()->getName()
279     << "' with floating point type '" << drCond->getType().getAsString()
280     << "' should not be used as a loop counter";
281
282  ranges.push_back(drCond->getSourceRange());
283  ranges.push_back(drInc->getSourceRange());
284
285  const char *bugType = "Floating point variable used as loop counter";
286
287  PathDiagnosticLocation FSLoc =
288    PathDiagnosticLocation::createBegin(FS, BR.getSourceManager(), AC);
289  BR.EmitBasicReport(bugType, "Security", os.str(),
290                     FSLoc, ranges.data(), ranges.size());
291}
292
293//===----------------------------------------------------------------------===//
294// Check: Any use of 'gets' is insecure.
295// Originally: <rdar://problem/6335715>
296// Implements (part of): 300-BSI (buildsecurityin.us-cert.gov)
297// CWE-242: Use of Inherently Dangerous Function
298//===----------------------------------------------------------------------===//
299
300void WalkAST::checkCall_gets(const CallExpr *CE, const FunctionDecl *FD) {
301  if (!filter.check_gets)
302    return;
303
304  const FunctionProtoType *FPT
305    = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens());
306  if (!FPT)
307    return;
308
309  // Verify that the function takes a single argument.
310  if (FPT->getNumArgs() != 1)
311    return;
312
313  // Is the argument a 'char*'?
314  const PointerType *PT = dyn_cast<PointerType>(FPT->getArgType(0));
315  if (!PT)
316    return;
317
318  if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
319    return;
320
321  // Issue a warning.
322  SourceRange R = CE->getCallee()->getSourceRange();
323  PathDiagnosticLocation CELoc =
324    PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
325  BR.EmitBasicReport("Potential buffer overflow in call to 'gets'",
326                     "Security",
327                     "Call to function 'gets' is extremely insecure as it can "
328                     "always result in a buffer overflow",
329                     CELoc, &R, 1);
330}
331
332//===----------------------------------------------------------------------===//
333// Check: Any use of 'getpwd' is insecure.
334// CWE-477: Use of Obsolete Functions
335//===----------------------------------------------------------------------===//
336
337void WalkAST::checkCall_getpw(const CallExpr *CE, const FunctionDecl *FD) {
338  if (!filter.check_getpw)
339    return;
340
341  const FunctionProtoType *FPT
342    = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens());
343  if (!FPT)
344    return;
345
346  // Verify that the function takes two arguments.
347  if (FPT->getNumArgs() != 2)
348    return;
349
350  // Verify the first argument type is integer.
351  if (!FPT->getArgType(0)->isIntegerType())
352    return;
353
354  // Verify the second argument type is char*.
355  const PointerType *PT = dyn_cast<PointerType>(FPT->getArgType(1));
356  if (!PT)
357    return;
358
359  if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
360    return;
361
362  // Issue a warning.
363  SourceRange R = CE->getCallee()->getSourceRange();
364  PathDiagnosticLocation CELoc =
365    PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
366  BR.EmitBasicReport("Potential buffer overflow in call to 'getpw'",
367                     "Security",
368                     "The getpw() function is dangerous as it may overflow the "
369                     "provided buffer. It is obsoleted by getpwuid().",
370                     CELoc, &R, 1);
371}
372
373//===----------------------------------------------------------------------===//
374// Check: Any use of 'mktemp' is insecure.  It is obsoleted by mkstemp().
375// CWE-377: Insecure Temporary File
376//===----------------------------------------------------------------------===//
377
378void WalkAST::checkCall_mktemp(const CallExpr *CE, const FunctionDecl *FD) {
379  if (!filter.check_mktemp) {
380    // Fall back to the security check of looking for enough 'X's in the
381    // format string, since that is a less severe warning.
382    checkCall_mkstemp(CE, FD);
383    return;
384  }
385
386  const FunctionProtoType *FPT
387    = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens());
388  if(!FPT)
389    return;
390
391  // Verify that the function takes a single argument.
392  if (FPT->getNumArgs() != 1)
393    return;
394
395  // Verify that the argument is Pointer Type.
396  const PointerType *PT = dyn_cast<PointerType>(FPT->getArgType(0));
397  if (!PT)
398    return;
399
400  // Verify that the argument is a 'char*'.
401  if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
402    return;
403
404  // Issue a waring.
405  SourceRange R = CE->getCallee()->getSourceRange();
406  PathDiagnosticLocation CELoc =
407    PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
408  BR.EmitBasicReport("Potential insecure temporary file in call 'mktemp'",
409                     "Security",
410                     "Call to function 'mktemp' is insecure as it always "
411                     "creates or uses insecure temporary file.  Use 'mkstemp' instead",
412                     CELoc, &R, 1);
413}
414
415
416//===----------------------------------------------------------------------===//
417// Check: Use of 'mkstemp', 'mktemp', 'mkdtemp' should contain at least 6 X's.
418//===----------------------------------------------------------------------===//
419
420void WalkAST::checkCall_mkstemp(const CallExpr *CE, const FunctionDecl *FD) {
421  if (!filter.check_mkstemp)
422    return;
423
424  StringRef Name = FD->getIdentifier()->getName();
425  std::pair<signed, signed> ArgSuffix =
426    llvm::StringSwitch<std::pair<signed, signed> >(Name)
427      .Case("mktemp", std::make_pair(0,-1))
428      .Case("mkstemp", std::make_pair(0,-1))
429      .Case("mkdtemp", std::make_pair(0,-1))
430      .Case("mkstemps", std::make_pair(0,1))
431      .Default(std::make_pair(-1, -1));
432
433  assert(ArgSuffix.first >= 0 && "Unsupported function");
434
435  // Check if the number of arguments is consistent with out expectations.
436  unsigned numArgs = CE->getNumArgs();
437  if ((signed) numArgs <= ArgSuffix.first)
438    return;
439
440  const StringLiteral *strArg =
441    dyn_cast<StringLiteral>(CE->getArg((unsigned)ArgSuffix.first)
442                              ->IgnoreParenImpCasts());
443
444  // Currently we only handle string literals.  It is possible to do better,
445  // either by looking at references to const variables, or by doing real
446  // flow analysis.
447  if (!strArg || strArg->getCharByteWidth() != 1)
448    return;
449
450  // Count the number of X's, taking into account a possible cutoff suffix.
451  StringRef str = strArg->getString();
452  unsigned numX = 0;
453  unsigned n = str.size();
454
455  // Take into account the suffix.
456  unsigned suffix = 0;
457  if (ArgSuffix.second >= 0) {
458    const Expr *suffixEx = CE->getArg((unsigned)ArgSuffix.second);
459    llvm::APSInt Result;
460    if (!suffixEx->EvaluateAsInt(Result, BR.getContext()))
461      return;
462    // FIXME: Issue a warning.
463    if (Result.isNegative())
464      return;
465    suffix = (unsigned) Result.getZExtValue();
466    n = (n > suffix) ? n - suffix : 0;
467  }
468
469  for (unsigned i = 0; i < n; ++i)
470    if (str[i] == 'X') ++numX;
471
472  if (numX >= 6)
473    return;
474
475  // Issue a warning.
476  SourceRange R = strArg->getSourceRange();
477  PathDiagnosticLocation CELoc =
478    PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
479  SmallString<512> buf;
480  llvm::raw_svector_ostream out(buf);
481  out << "Call to '" << Name << "' should have at least 6 'X's in the"
482    " format string to be secure (" << numX << " 'X'";
483  if (numX != 1)
484    out << 's';
485  out << " seen";
486  if (suffix) {
487    out << ", " << suffix << " character";
488    if (suffix > 1)
489      out << 's';
490    out << " used as a suffix";
491  }
492  out << ')';
493  BR.EmitBasicReport("Insecure temporary file creation", "Security",
494                     out.str(), CELoc, &R, 1);
495}
496
497//===----------------------------------------------------------------------===//
498// Check: Any use of 'strcpy' is insecure.
499//
500// CWE-119: Improper Restriction of Operations within
501// the Bounds of a Memory Buffer
502//===----------------------------------------------------------------------===//
503void WalkAST::checkCall_strcpy(const CallExpr *CE, const FunctionDecl *FD) {
504  if (!filter.check_strcpy)
505    return;
506
507  if (!checkCall_strCommon(CE, FD))
508    return;
509
510  // Issue a warning.
511  SourceRange R = CE->getCallee()->getSourceRange();
512  PathDiagnosticLocation CELoc =
513    PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
514  BR.EmitBasicReport("Potential insecure memory buffer bounds restriction in "
515                     "call 'strcpy'",
516                     "Security",
517                     "Call to function 'strcpy' is insecure as it does not "
518		     "provide bounding of the memory buffer. Replace "
519		     "unbounded copy functions with analogous functions that "
520		     "support length arguments such as 'strlcpy'. CWE-119.",
521                     CELoc, &R, 1);
522}
523
524//===----------------------------------------------------------------------===//
525// Check: Any use of 'strcat' is insecure.
526//
527// CWE-119: Improper Restriction of Operations within
528// the Bounds of a Memory Buffer
529//===----------------------------------------------------------------------===//
530void WalkAST::checkCall_strcat(const CallExpr *CE, const FunctionDecl *FD) {
531  if (!filter.check_strcpy)
532    return;
533
534  if (!checkCall_strCommon(CE, FD))
535    return;
536
537  // Issue a warning.
538  SourceRange R = CE->getCallee()->getSourceRange();
539  PathDiagnosticLocation CELoc =
540    PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
541  BR.EmitBasicReport("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
556    = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens());
557  if (!FPT)
558    return false;
559
560  // Verify the function takes two arguments, three in the _chk version.
561  int numArgs = FPT->getNumArgs();
562  if (numArgs != 2 && numArgs != 3)
563    return false;
564
565  // Verify the type for both arguments.
566  for (int i = 0; i < 2; i++) {
567    // Verify that the arguments are pointers.
568    const PointerType *PT = dyn_cast<PointerType>(FPT->getArgType(i));
569    if (!PT)
570      return false;
571
572    // Verify that the argument is a 'char*'.
573    if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
574      return false;
575  }
576
577  return true;
578}
579
580//===----------------------------------------------------------------------===//
581// Check: Linear congruent random number generators should not be used
582// Originally: <rdar://problem/63371000>
583// CWE-338: Use of cryptographically weak prng
584//===----------------------------------------------------------------------===//
585
586void WalkAST::checkCall_rand(const CallExpr *CE, const FunctionDecl *FD) {
587  if (!filter.check_rand || !CheckRand)
588    return;
589
590  const FunctionProtoType *FTP
591    = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens());
592  if (!FTP)
593    return;
594
595  if (FTP->getNumArgs() == 1) {
596    // Is the argument an 'unsigned short *'?
597    // (Actually any integer type is allowed.)
598    const PointerType *PT = dyn_cast<PointerType>(FTP->getArgType(0));
599    if (!PT)
600      return;
601
602    if (! PT->getPointeeType()->isIntegerType())
603      return;
604  }
605  else if (FTP->getNumArgs() != 0)
606    return;
607
608  // Issue a warning.
609  SmallString<256> buf1;
610  llvm::raw_svector_ostream os1(buf1);
611  os1 << '\'' << *FD << "' is a poor random number generator";
612
613  SmallString<256> buf2;
614  llvm::raw_svector_ostream os2(buf2);
615  os2 << "Function '" << *FD
616      << "' is obsolete because it implements a poor random number generator."
617      << "  Use 'arc4random' instead";
618
619  SourceRange R = CE->getCallee()->getSourceRange();
620  PathDiagnosticLocation CELoc =
621    PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
622  BR.EmitBasicReport(os1.str(), "Security", os2.str(), CELoc, &R, 1);
623}
624
625//===----------------------------------------------------------------------===//
626// Check: 'random' should not be used
627// Originally: <rdar://problem/63371000>
628//===----------------------------------------------------------------------===//
629
630void WalkAST::checkCall_random(const CallExpr *CE, const FunctionDecl *FD) {
631  if (!CheckRand || !filter.check_rand)
632    return;
633
634  const FunctionProtoType *FTP
635    = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens());
636  if (!FTP)
637    return;
638
639  // Verify that the function takes no argument.
640  if (FTP->getNumArgs() != 0)
641    return;
642
643  // Issue a warning.
644  SourceRange R = CE->getCallee()->getSourceRange();
645  PathDiagnosticLocation CELoc =
646    PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
647  BR.EmitBasicReport("'random' is not a secure random number generator",
648                     "Security",
649                     "The 'random' function produces a sequence of values that "
650                     "an adversary may be able to predict.  Use 'arc4random' "
651                     "instead", CELoc, &R, 1);
652}
653
654//===----------------------------------------------------------------------===//
655// Check: 'vfork' should not be used.
656// POS33-C: Do not use vfork().
657//===----------------------------------------------------------------------===//
658
659void WalkAST::checkCall_vfork(const CallExpr *CE, const FunctionDecl *FD) {
660  if (!filter.check_vfork)
661    return;
662
663  // All calls to vfork() are insecure, issue a warning.
664  SourceRange R = CE->getCallee()->getSourceRange();
665  PathDiagnosticLocation CELoc =
666    PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
667  BR.EmitBasicReport("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
711    = dyn_cast<FunctionProtoType>(FD->getType().IgnoreParens());
712  if (!FTP)
713    return;
714
715  // Verify that the function takes one or two arguments (depending on
716  //   the function).
717  if (FTP->getNumArgs() != (identifierid < 4 ? 1 : 2))
718    return;
719
720  // The arguments must be integers.
721  for (unsigned i = 0; i < FTP->getNumArgs(); i++)
722    if (! FTP->getArgType(i)->isIntegerType())
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  SourceRange R = CE->getCallee()->getSourceRange();
737  PathDiagnosticLocation CELoc =
738    PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
739  BR.EmitBasicReport(os1.str(), "Security", os2.str(), 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