1 //==- CheckSecuritySyntaxOnly.cpp - Basic security checks --------*- C++ -*-==//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 //  This file defines a set of flow-insensitive security checks.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
15 #include "clang/AST/StmtVisitor.h"
16 #include "clang/Analysis/AnalysisDeclContext.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 
25 using namespace clang;
26 using namespace ento;
27 
isArc4RandomAvailable(const ASTContext & Ctx)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.isOSFreeBSD() ||
33          T.isOSNetBSD() ||
34          T.isOSOpenBSD() ||
35          T.isOSDragonFly();
36 }
37 
38 namespace {
39 struct ChecksFilter {
40   DefaultBool check_bcmp;
41   DefaultBool check_bcopy;
42   DefaultBool check_bzero;
43   DefaultBool check_gets;
44   DefaultBool check_getpw;
45   DefaultBool check_mktemp;
46   DefaultBool check_mkstemp;
47   DefaultBool check_strcpy;
48   DefaultBool check_rand;
49   DefaultBool check_vfork;
50   DefaultBool check_FloatLoopCounter;
51   DefaultBool check_UncheckedReturn;
52 
53   CheckName checkName_bcmp;
54   CheckName checkName_bcopy;
55   CheckName checkName_bzero;
56   CheckName checkName_gets;
57   CheckName checkName_getpw;
58   CheckName checkName_mktemp;
59   CheckName checkName_mkstemp;
60   CheckName checkName_strcpy;
61   CheckName checkName_rand;
62   CheckName checkName_vfork;
63   CheckName checkName_FloatLoopCounter;
64   CheckName checkName_UncheckedReturn;
65 };
66 
67 class WalkAST : public StmtVisitor<WalkAST> {
68   BugReporter &BR;
69   AnalysisDeclContext* AC;
70   enum { num_setids = 6 };
71   IdentifierInfo *II_setid[num_setids];
72 
73   const bool CheckRand;
74   const ChecksFilter &filter;
75 
76 public:
WalkAST(BugReporter & br,AnalysisDeclContext * ac,const ChecksFilter & f)77   WalkAST(BugReporter &br, AnalysisDeclContext* ac,
78           const ChecksFilter &f)
79   : BR(br), AC(ac), II_setid(),
80     CheckRand(isArc4RandomAvailable(BR.getContext())),
81     filter(f) {}
82 
83   // Statement visitor methods.
84   void VisitCallExpr(CallExpr *CE);
85   void VisitForStmt(ForStmt *S);
86   void VisitCompoundStmt (CompoundStmt *S);
VisitStmt(Stmt * S)87   void VisitStmt(Stmt *S) { VisitChildren(S); }
88 
89   void VisitChildren(Stmt *S);
90 
91   // Helpers.
92   bool checkCall_strCommon(const CallExpr *CE, const FunctionDecl *FD);
93 
94   typedef void (WalkAST::*FnCheck)(const CallExpr *, const FunctionDecl *);
95 
96   // Checker-specific methods.
97   void checkLoopConditionForFloat(const ForStmt *FS);
98   void checkCall_bcmp(const CallExpr *CE, const FunctionDecl *FD);
99   void checkCall_bcopy(const CallExpr *CE, const FunctionDecl *FD);
100   void checkCall_bzero(const CallExpr *CE, const FunctionDecl *FD);
101   void checkCall_gets(const CallExpr *CE, const FunctionDecl *FD);
102   void checkCall_getpw(const CallExpr *CE, const FunctionDecl *FD);
103   void checkCall_mktemp(const CallExpr *CE, const FunctionDecl *FD);
104   void checkCall_mkstemp(const CallExpr *CE, const FunctionDecl *FD);
105   void checkCall_strcpy(const CallExpr *CE, const FunctionDecl *FD);
106   void checkCall_strcat(const CallExpr *CE, const FunctionDecl *FD);
107   void checkCall_rand(const CallExpr *CE, const FunctionDecl *FD);
108   void checkCall_random(const CallExpr *CE, const FunctionDecl *FD);
109   void checkCall_vfork(const CallExpr *CE, const FunctionDecl *FD);
110   void checkUncheckedReturnValue(CallExpr *CE);
111 };
112 } // end anonymous namespace
113 
114 //===----------------------------------------------------------------------===//
115 // AST walking.
116 //===----------------------------------------------------------------------===//
117 
VisitChildren(Stmt * S)118 void WalkAST::VisitChildren(Stmt *S) {
119   for (Stmt *Child : S->children())
120     if (Child)
121       Visit(Child);
122 }
123 
VisitCallExpr(CallExpr * CE)124 void WalkAST::VisitCallExpr(CallExpr *CE) {
125   // Get the callee.
126   const FunctionDecl *FD = CE->getDirectCallee();
127 
128   if (!FD)
129     return;
130 
131   // Get the name of the callee. If it's a builtin, strip off the prefix.
132   IdentifierInfo *II = FD->getIdentifier();
133   if (!II)   // if no identifier, not a simple C function
134     return;
135   StringRef Name = II->getName();
136   if (Name.startswith("__builtin_"))
137     Name = Name.substr(10);
138 
139   // Set the evaluation function by switching on the callee name.
140   FnCheck evalFunction = llvm::StringSwitch<FnCheck>(Name)
141     .Case("bcmp", &WalkAST::checkCall_bcmp)
142     .Case("bcopy", &WalkAST::checkCall_bcopy)
143     .Case("bzero", &WalkAST::checkCall_bzero)
144     .Case("gets", &WalkAST::checkCall_gets)
145     .Case("getpw", &WalkAST::checkCall_getpw)
146     .Case("mktemp", &WalkAST::checkCall_mktemp)
147     .Case("mkstemp", &WalkAST::checkCall_mkstemp)
148     .Case("mkdtemp", &WalkAST::checkCall_mkstemp)
149     .Case("mkstemps", &WalkAST::checkCall_mkstemp)
150     .Cases("strcpy", "__strcpy_chk", &WalkAST::checkCall_strcpy)
151     .Cases("strcat", "__strcat_chk", &WalkAST::checkCall_strcat)
152     .Case("drand48", &WalkAST::checkCall_rand)
153     .Case("erand48", &WalkAST::checkCall_rand)
154     .Case("jrand48", &WalkAST::checkCall_rand)
155     .Case("lrand48", &WalkAST::checkCall_rand)
156     .Case("mrand48", &WalkAST::checkCall_rand)
157     .Case("nrand48", &WalkAST::checkCall_rand)
158     .Case("lcong48", &WalkAST::checkCall_rand)
159     .Case("rand", &WalkAST::checkCall_rand)
160     .Case("rand_r", &WalkAST::checkCall_rand)
161     .Case("random", &WalkAST::checkCall_random)
162     .Case("vfork", &WalkAST::checkCall_vfork)
163     .Default(nullptr);
164 
165   // If the callee isn't defined, it is not of security concern.
166   // Check and evaluate the call.
167   if (evalFunction)
168     (this->*evalFunction)(CE, FD);
169 
170   // Recurse and check children.
171   VisitChildren(CE);
172 }
173 
VisitCompoundStmt(CompoundStmt * S)174 void WalkAST::VisitCompoundStmt(CompoundStmt *S) {
175   for (Stmt *Child : S->children())
176     if (Child) {
177       if (CallExpr *CE = dyn_cast<CallExpr>(Child))
178         checkUncheckedReturnValue(CE);
179       Visit(Child);
180     }
181 }
182 
VisitForStmt(ForStmt * FS)183 void WalkAST::VisitForStmt(ForStmt *FS) {
184   checkLoopConditionForFloat(FS);
185 
186   // Recurse and check children.
187   VisitChildren(FS);
188 }
189 
190 //===----------------------------------------------------------------------===//
191 // Check: floating point variable used as loop counter.
192 // Originally: <rdar://problem/6336718>
193 // Implements: CERT security coding advisory FLP-30.
194 //===----------------------------------------------------------------------===//
195 
196 static const DeclRefExpr*
getIncrementedVar(const Expr * expr,const VarDecl * x,const VarDecl * y)197 getIncrementedVar(const Expr *expr, const VarDecl *x, const VarDecl *y) {
198   expr = expr->IgnoreParenCasts();
199 
200   if (const BinaryOperator *B = dyn_cast<BinaryOperator>(expr)) {
201     if (!(B->isAssignmentOp() || B->isCompoundAssignmentOp() ||
202           B->getOpcode() == BO_Comma))
203       return nullptr;
204 
205     if (const DeclRefExpr *lhs = getIncrementedVar(B->getLHS(), x, y))
206       return lhs;
207 
208     if (const DeclRefExpr *rhs = getIncrementedVar(B->getRHS(), x, y))
209       return rhs;
210 
211     return nullptr;
212   }
213 
214   if (const DeclRefExpr *DR = dyn_cast<DeclRefExpr>(expr)) {
215     const NamedDecl *ND = DR->getDecl();
216     return ND == x || ND == y ? DR : nullptr;
217   }
218 
219   if (const UnaryOperator *U = dyn_cast<UnaryOperator>(expr))
220     return U->isIncrementDecrementOp()
221       ? getIncrementedVar(U->getSubExpr(), x, y) : nullptr;
222 
223   return nullptr;
224 }
225 
226 /// CheckLoopConditionForFloat - This check looks for 'for' statements that
227 ///  use a floating point variable as a loop counter.
228 ///  CERT: FLP30-C, FLP30-CPP.
229 ///
checkLoopConditionForFloat(const ForStmt * FS)230 void WalkAST::checkLoopConditionForFloat(const ForStmt *FS) {
231   if (!filter.check_FloatLoopCounter)
232     return;
233 
234   // Does the loop have a condition?
235   const Expr *condition = FS->getCond();
236 
237   if (!condition)
238     return;
239 
240   // Does the loop have an increment?
241   const Expr *increment = FS->getInc();
242 
243   if (!increment)
244     return;
245 
246   // Strip away '()' and casts.
247   condition = condition->IgnoreParenCasts();
248   increment = increment->IgnoreParenCasts();
249 
250   // Is the loop condition a comparison?
251   const BinaryOperator *B = dyn_cast<BinaryOperator>(condition);
252 
253   if (!B)
254     return;
255 
256   // Is this a comparison?
257   if (!(B->isRelationalOp() || B->isEqualityOp()))
258     return;
259 
260   // Are we comparing variables?
261   const DeclRefExpr *drLHS =
262     dyn_cast<DeclRefExpr>(B->getLHS()->IgnoreParenLValueCasts());
263   const DeclRefExpr *drRHS =
264     dyn_cast<DeclRefExpr>(B->getRHS()->IgnoreParenLValueCasts());
265 
266   // Does at least one of the variables have a floating point type?
267   drLHS = drLHS && drLHS->getType()->isRealFloatingType() ? drLHS : nullptr;
268   drRHS = drRHS && drRHS->getType()->isRealFloatingType() ? drRHS : nullptr;
269 
270   if (!drLHS && !drRHS)
271     return;
272 
273   const VarDecl *vdLHS = drLHS ? dyn_cast<VarDecl>(drLHS->getDecl()) : nullptr;
274   const VarDecl *vdRHS = drRHS ? dyn_cast<VarDecl>(drRHS->getDecl()) : nullptr;
275 
276   if (!vdLHS && !vdRHS)
277     return;
278 
279   // Does either variable appear in increment?
280   const DeclRefExpr *drInc = getIncrementedVar(increment, vdLHS, vdRHS);
281 
282   if (!drInc)
283     return;
284 
285   // Emit the error.  First figure out which DeclRefExpr in the condition
286   // referenced the compared variable.
287   assert(drInc->getDecl());
288   const DeclRefExpr *drCond = vdLHS == drInc->getDecl() ? drLHS : drRHS;
289 
290   SmallVector<SourceRange, 2> ranges;
291   SmallString<256> sbuf;
292   llvm::raw_svector_ostream os(sbuf);
293 
294   os << "Variable '" << drCond->getDecl()->getName()
295      << "' with floating point type '" << drCond->getType().getAsString()
296      << "' should not be used as a loop counter";
297 
298   ranges.push_back(drCond->getSourceRange());
299   ranges.push_back(drInc->getSourceRange());
300 
301   const char *bugType = "Floating point variable used as loop counter";
302 
303   PathDiagnosticLocation FSLoc =
304     PathDiagnosticLocation::createBegin(FS, BR.getSourceManager(), AC);
305   BR.EmitBasicReport(AC->getDecl(), filter.checkName_FloatLoopCounter,
306                      bugType, "Security", os.str(),
307                      FSLoc, ranges);
308 }
309 
310 //===----------------------------------------------------------------------===//
311 // Check: Any use of bcmp.
312 // CWE-477: Use of Obsolete Functions
313 // bcmp was deprecated in POSIX.1-2008
314 //===----------------------------------------------------------------------===//
315 
checkCall_bcmp(const CallExpr * CE,const FunctionDecl * FD)316 void WalkAST::checkCall_bcmp(const CallExpr *CE, const FunctionDecl *FD) {
317   if (!filter.check_bcmp)
318     return;
319 
320   const FunctionProtoType *FPT = FD->getType()->getAs<FunctionProtoType>();
321   if (!FPT)
322     return;
323 
324   // Verify that the function takes three arguments.
325   if (FPT->getNumParams() != 3)
326     return;
327 
328   for (int i = 0; i < 2; i++) {
329     // Verify the first and second argument type is void*.
330     const PointerType *PT = FPT->getParamType(i)->getAs<PointerType>();
331     if (!PT)
332       return;
333 
334     if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().VoidTy)
335       return;
336   }
337 
338   // Verify the third argument type is integer.
339   if (!FPT->getParamType(2)->isIntegralOrUnscopedEnumerationType())
340     return;
341 
342   // Issue a warning.
343   PathDiagnosticLocation CELoc =
344     PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
345   BR.EmitBasicReport(AC->getDecl(), filter.checkName_bcmp,
346                      "Use of deprecated function in call to 'bcmp()'",
347                      "Security",
348                      "The bcmp() function is obsoleted by memcmp().",
349                      CELoc, CE->getCallee()->getSourceRange());
350 }
351 
352 //===----------------------------------------------------------------------===//
353 // Check: Any use of bcopy.
354 // CWE-477: Use of Obsolete Functions
355 // bcopy was deprecated in POSIX.1-2008
356 //===----------------------------------------------------------------------===//
357 
checkCall_bcopy(const CallExpr * CE,const FunctionDecl * FD)358 void WalkAST::checkCall_bcopy(const CallExpr *CE, const FunctionDecl *FD) {
359   if (!filter.check_bcopy)
360     return;
361 
362   const FunctionProtoType *FPT = FD->getType()->getAs<FunctionProtoType>();
363   if (!FPT)
364     return;
365 
366   // Verify that the function takes three arguments.
367   if (FPT->getNumParams() != 3)
368     return;
369 
370   for (int i = 0; i < 2; i++) {
371     // Verify the first and second argument type is void*.
372     const PointerType *PT = FPT->getParamType(i)->getAs<PointerType>();
373     if (!PT)
374       return;
375 
376     if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().VoidTy)
377       return;
378   }
379 
380   // Verify the third argument type is integer.
381   if (!FPT->getParamType(2)->isIntegralOrUnscopedEnumerationType())
382     return;
383 
384   // Issue a warning.
385   PathDiagnosticLocation CELoc =
386     PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
387   BR.EmitBasicReport(AC->getDecl(), filter.checkName_bcopy,
388                      "Use of deprecated function in call to 'bcopy()'",
389                      "Security",
390                      "The bcopy() function is obsoleted by memcpy() "
391                      "or memmove().",
392                      CELoc, CE->getCallee()->getSourceRange());
393 }
394 
395 //===----------------------------------------------------------------------===//
396 // Check: Any use of bzero.
397 // CWE-477: Use of Obsolete Functions
398 // bzero was deprecated in POSIX.1-2008
399 //===----------------------------------------------------------------------===//
400 
checkCall_bzero(const CallExpr * CE,const FunctionDecl * FD)401 void WalkAST::checkCall_bzero(const CallExpr *CE, const FunctionDecl *FD) {
402   if (!filter.check_bzero)
403     return;
404 
405   const FunctionProtoType *FPT = FD->getType()->getAs<FunctionProtoType>();
406   if (!FPT)
407     return;
408 
409   // Verify that the function takes two arguments.
410   if (FPT->getNumParams() != 2)
411     return;
412 
413   // Verify the first argument type is void*.
414   const PointerType *PT = FPT->getParamType(0)->getAs<PointerType>();
415   if (!PT)
416     return;
417 
418   if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().VoidTy)
419     return;
420 
421   // Verify the second argument type is integer.
422   if (!FPT->getParamType(1)->isIntegralOrUnscopedEnumerationType())
423     return;
424 
425   // Issue a warning.
426   PathDiagnosticLocation CELoc =
427     PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
428   BR.EmitBasicReport(AC->getDecl(), filter.checkName_bzero,
429                      "Use of deprecated function in call to 'bzero()'",
430                      "Security",
431                      "The bzero() function is obsoleted by memset().",
432                      CELoc, CE->getCallee()->getSourceRange());
433 }
434 
435 
436 //===----------------------------------------------------------------------===//
437 // Check: Any use of 'gets' is insecure.
438 // Originally: <rdar://problem/6335715>
439 // Implements (part of): 300-BSI (buildsecurityin.us-cert.gov)
440 // CWE-242: Use of Inherently Dangerous Function
441 //===----------------------------------------------------------------------===//
442 
checkCall_gets(const CallExpr * CE,const FunctionDecl * FD)443 void WalkAST::checkCall_gets(const CallExpr *CE, const FunctionDecl *FD) {
444   if (!filter.check_gets)
445     return;
446 
447   const FunctionProtoType *FPT = FD->getType()->getAs<FunctionProtoType>();
448   if (!FPT)
449     return;
450 
451   // Verify that the function takes a single argument.
452   if (FPT->getNumParams() != 1)
453     return;
454 
455   // Is the argument a 'char*'?
456   const PointerType *PT = FPT->getParamType(0)->getAs<PointerType>();
457   if (!PT)
458     return;
459 
460   if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
461     return;
462 
463   // Issue a warning.
464   PathDiagnosticLocation CELoc =
465     PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
466   BR.EmitBasicReport(AC->getDecl(), filter.checkName_gets,
467                      "Potential buffer overflow in call to 'gets'",
468                      "Security",
469                      "Call to function 'gets' is extremely insecure as it can "
470                      "always result in a buffer overflow",
471                      CELoc, CE->getCallee()->getSourceRange());
472 }
473 
474 //===----------------------------------------------------------------------===//
475 // Check: Any use of 'getpwd' is insecure.
476 // CWE-477: Use of Obsolete Functions
477 //===----------------------------------------------------------------------===//
478 
checkCall_getpw(const CallExpr * CE,const FunctionDecl * FD)479 void WalkAST::checkCall_getpw(const CallExpr *CE, const FunctionDecl *FD) {
480   if (!filter.check_getpw)
481     return;
482 
483   const FunctionProtoType *FPT = FD->getType()->getAs<FunctionProtoType>();
484   if (!FPT)
485     return;
486 
487   // Verify that the function takes two arguments.
488   if (FPT->getNumParams() != 2)
489     return;
490 
491   // Verify the first argument type is integer.
492   if (!FPT->getParamType(0)->isIntegralOrUnscopedEnumerationType())
493     return;
494 
495   // Verify the second argument type is char*.
496   const PointerType *PT = FPT->getParamType(1)->getAs<PointerType>();
497   if (!PT)
498     return;
499 
500   if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
501     return;
502 
503   // Issue a warning.
504   PathDiagnosticLocation CELoc =
505     PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
506   BR.EmitBasicReport(AC->getDecl(), filter.checkName_getpw,
507                      "Potential buffer overflow in call to 'getpw'",
508                      "Security",
509                      "The getpw() function is dangerous as it may overflow the "
510                      "provided buffer. It is obsoleted by getpwuid().",
511                      CELoc, CE->getCallee()->getSourceRange());
512 }
513 
514 //===----------------------------------------------------------------------===//
515 // Check: Any use of 'mktemp' is insecure.  It is obsoleted by mkstemp().
516 // CWE-377: Insecure Temporary File
517 //===----------------------------------------------------------------------===//
518 
checkCall_mktemp(const CallExpr * CE,const FunctionDecl * FD)519 void WalkAST::checkCall_mktemp(const CallExpr *CE, const FunctionDecl *FD) {
520   if (!filter.check_mktemp) {
521     // Fall back to the security check of looking for enough 'X's in the
522     // format string, since that is a less severe warning.
523     checkCall_mkstemp(CE, FD);
524     return;
525   }
526 
527   const FunctionProtoType *FPT = FD->getType()->getAs<FunctionProtoType>();
528   if(!FPT)
529     return;
530 
531   // Verify that the function takes a single argument.
532   if (FPT->getNumParams() != 1)
533     return;
534 
535   // Verify that the argument is Pointer Type.
536   const PointerType *PT = FPT->getParamType(0)->getAs<PointerType>();
537   if (!PT)
538     return;
539 
540   // Verify that the argument is a 'char*'.
541   if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
542     return;
543 
544   // Issue a warning.
545   PathDiagnosticLocation CELoc =
546     PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
547   BR.EmitBasicReport(AC->getDecl(), filter.checkName_mktemp,
548                      "Potential insecure temporary file in call 'mktemp'",
549                      "Security",
550                      "Call to function 'mktemp' is insecure as it always "
551                      "creates or uses insecure temporary file.  Use 'mkstemp' "
552                      "instead",
553                      CELoc, CE->getCallee()->getSourceRange());
554 }
555 
556 
557 //===----------------------------------------------------------------------===//
558 // Check: Use of 'mkstemp', 'mktemp', 'mkdtemp' should contain at least 6 X's.
559 //===----------------------------------------------------------------------===//
560 
checkCall_mkstemp(const CallExpr * CE,const FunctionDecl * FD)561 void WalkAST::checkCall_mkstemp(const CallExpr *CE, const FunctionDecl *FD) {
562   if (!filter.check_mkstemp)
563     return;
564 
565   StringRef Name = FD->getIdentifier()->getName();
566   std::pair<signed, signed> ArgSuffix =
567     llvm::StringSwitch<std::pair<signed, signed> >(Name)
568       .Case("mktemp", std::make_pair(0,-1))
569       .Case("mkstemp", std::make_pair(0,-1))
570       .Case("mkdtemp", std::make_pair(0,-1))
571       .Case("mkstemps", std::make_pair(0,1))
572       .Default(std::make_pair(-1, -1));
573 
574   assert(ArgSuffix.first >= 0 && "Unsupported function");
575 
576   // Check if the number of arguments is consistent with out expectations.
577   unsigned numArgs = CE->getNumArgs();
578   if ((signed) numArgs <= ArgSuffix.first)
579     return;
580 
581   const StringLiteral *strArg =
582     dyn_cast<StringLiteral>(CE->getArg((unsigned)ArgSuffix.first)
583                               ->IgnoreParenImpCasts());
584 
585   // Currently we only handle string literals.  It is possible to do better,
586   // either by looking at references to const variables, or by doing real
587   // flow analysis.
588   if (!strArg || strArg->getCharByteWidth() != 1)
589     return;
590 
591   // Count the number of X's, taking into account a possible cutoff suffix.
592   StringRef str = strArg->getString();
593   unsigned numX = 0;
594   unsigned n = str.size();
595 
596   // Take into account the suffix.
597   unsigned suffix = 0;
598   if (ArgSuffix.second >= 0) {
599     const Expr *suffixEx = CE->getArg((unsigned)ArgSuffix.second);
600     Expr::EvalResult EVResult;
601     if (!suffixEx->EvaluateAsInt(EVResult, BR.getContext()))
602       return;
603     llvm::APSInt Result = EVResult.Val.getInt();
604     // FIXME: Issue a warning.
605     if (Result.isNegative())
606       return;
607     suffix = (unsigned) Result.getZExtValue();
608     n = (n > suffix) ? n - suffix : 0;
609   }
610 
611   for (unsigned i = 0; i < n; ++i)
612     if (str[i] == 'X') ++numX;
613 
614   if (numX >= 6)
615     return;
616 
617   // Issue a warning.
618   PathDiagnosticLocation CELoc =
619     PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
620   SmallString<512> buf;
621   llvm::raw_svector_ostream out(buf);
622   out << "Call to '" << Name << "' should have at least 6 'X's in the"
623     " format string to be secure (" << numX << " 'X'";
624   if (numX != 1)
625     out << 's';
626   out << " seen";
627   if (suffix) {
628     out << ", " << suffix << " character";
629     if (suffix > 1)
630       out << 's';
631     out << " used as a suffix";
632   }
633   out << ')';
634   BR.EmitBasicReport(AC->getDecl(), filter.checkName_mkstemp,
635                      "Insecure temporary file creation", "Security",
636                      out.str(), CELoc, strArg->getSourceRange());
637 }
638 
639 //===----------------------------------------------------------------------===//
640 // Check: Any use of 'strcpy' is insecure.
641 //
642 // CWE-119: Improper Restriction of Operations within
643 // the Bounds of a Memory Buffer
644 //===----------------------------------------------------------------------===//
checkCall_strcpy(const CallExpr * CE,const FunctionDecl * FD)645 void WalkAST::checkCall_strcpy(const CallExpr *CE, const FunctionDecl *FD) {
646   if (!filter.check_strcpy)
647     return;
648 
649   if (!checkCall_strCommon(CE, FD))
650     return;
651 
652   const auto *Target = CE->getArg(0)->IgnoreImpCasts(),
653              *Source = CE->getArg(1)->IgnoreImpCasts();
654 
655   if (const auto *Array = dyn_cast<ConstantArrayType>(Target->getType())) {
656     uint64_t ArraySize = BR.getContext().getTypeSize(Array) / 8;
657     if (const auto *String = dyn_cast<StringLiteral>(Source)) {
658       if (ArraySize >= String->getLength() + 1)
659         return;
660     }
661   }
662 
663   // Issue a warning.
664   PathDiagnosticLocation CELoc =
665     PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
666   BR.EmitBasicReport(AC->getDecl(), filter.checkName_strcpy,
667                      "Potential insecure memory buffer bounds restriction in "
668                      "call 'strcpy'",
669                      "Security",
670                      "Call to function 'strcpy' is insecure as it does not "
671                      "provide bounding of the memory buffer. Replace "
672                      "unbounded copy functions with analogous functions that "
673                      "support length arguments such as 'strlcpy'. CWE-119.",
674                      CELoc, CE->getCallee()->getSourceRange());
675 }
676 
677 //===----------------------------------------------------------------------===//
678 // Check: Any use of 'strcat' is insecure.
679 //
680 // CWE-119: Improper Restriction of Operations within
681 // the Bounds of a Memory Buffer
682 //===----------------------------------------------------------------------===//
checkCall_strcat(const CallExpr * CE,const FunctionDecl * FD)683 void WalkAST::checkCall_strcat(const CallExpr *CE, const FunctionDecl *FD) {
684   if (!filter.check_strcpy)
685     return;
686 
687   if (!checkCall_strCommon(CE, FD))
688     return;
689 
690   // Issue a warning.
691   PathDiagnosticLocation CELoc =
692     PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
693   BR.EmitBasicReport(AC->getDecl(), filter.checkName_strcpy,
694                      "Potential insecure memory buffer bounds restriction in "
695                      "call 'strcat'",
696                      "Security",
697                      "Call to function 'strcat' is insecure as it does not "
698                      "provide bounding of the memory buffer. Replace "
699                      "unbounded copy functions with analogous functions that "
700                      "support length arguments such as 'strlcat'. CWE-119.",
701                      CELoc, CE->getCallee()->getSourceRange());
702 }
703 
704 //===----------------------------------------------------------------------===//
705 // Common check for str* functions with no bounds parameters.
706 //===----------------------------------------------------------------------===//
checkCall_strCommon(const CallExpr * CE,const FunctionDecl * FD)707 bool WalkAST::checkCall_strCommon(const CallExpr *CE, const FunctionDecl *FD) {
708   const FunctionProtoType *FPT = FD->getType()->getAs<FunctionProtoType>();
709   if (!FPT)
710     return false;
711 
712   // Verify the function takes two arguments, three in the _chk version.
713   int numArgs = FPT->getNumParams();
714   if (numArgs != 2 && numArgs != 3)
715     return false;
716 
717   // Verify the type for both arguments.
718   for (int i = 0; i < 2; i++) {
719     // Verify that the arguments are pointers.
720     const PointerType *PT = FPT->getParamType(i)->getAs<PointerType>();
721     if (!PT)
722       return false;
723 
724     // Verify that the argument is a 'char*'.
725     if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
726       return false;
727   }
728 
729   return true;
730 }
731 
732 //===----------------------------------------------------------------------===//
733 // Check: Linear congruent random number generators should not be used
734 // Originally: <rdar://problem/63371000>
735 // CWE-338: Use of cryptographically weak prng
736 //===----------------------------------------------------------------------===//
737 
checkCall_rand(const CallExpr * CE,const FunctionDecl * FD)738 void WalkAST::checkCall_rand(const CallExpr *CE, const FunctionDecl *FD) {
739   if (!filter.check_rand || !CheckRand)
740     return;
741 
742   const FunctionProtoType *FTP = FD->getType()->getAs<FunctionProtoType>();
743   if (!FTP)
744     return;
745 
746   if (FTP->getNumParams() == 1) {
747     // Is the argument an 'unsigned short *'?
748     // (Actually any integer type is allowed.)
749     const PointerType *PT = FTP->getParamType(0)->getAs<PointerType>();
750     if (!PT)
751       return;
752 
753     if (! PT->getPointeeType()->isIntegralOrUnscopedEnumerationType())
754       return;
755   } else if (FTP->getNumParams() != 0)
756     return;
757 
758   // Issue a warning.
759   SmallString<256> buf1;
760   llvm::raw_svector_ostream os1(buf1);
761   os1 << '\'' << *FD << "' is a poor random number generator";
762 
763   SmallString<256> buf2;
764   llvm::raw_svector_ostream os2(buf2);
765   os2 << "Function '" << *FD
766       << "' is obsolete because it implements a poor random number generator."
767       << "  Use 'arc4random' instead";
768 
769   PathDiagnosticLocation CELoc =
770     PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
771   BR.EmitBasicReport(AC->getDecl(), filter.checkName_rand, os1.str(),
772                      "Security", os2.str(), CELoc,
773                      CE->getCallee()->getSourceRange());
774 }
775 
776 //===----------------------------------------------------------------------===//
777 // Check: 'random' should not be used
778 // Originally: <rdar://problem/63371000>
779 //===----------------------------------------------------------------------===//
780 
checkCall_random(const CallExpr * CE,const FunctionDecl * FD)781 void WalkAST::checkCall_random(const CallExpr *CE, const FunctionDecl *FD) {
782   if (!CheckRand || !filter.check_rand)
783     return;
784 
785   const FunctionProtoType *FTP = FD->getType()->getAs<FunctionProtoType>();
786   if (!FTP)
787     return;
788 
789   // Verify that the function takes no argument.
790   if (FTP->getNumParams() != 0)
791     return;
792 
793   // Issue a warning.
794   PathDiagnosticLocation CELoc =
795     PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
796   BR.EmitBasicReport(AC->getDecl(), filter.checkName_rand,
797                      "'random' is not a secure random number generator",
798                      "Security",
799                      "The 'random' function produces a sequence of values that "
800                      "an adversary may be able to predict.  Use 'arc4random' "
801                      "instead", CELoc, CE->getCallee()->getSourceRange());
802 }
803 
804 //===----------------------------------------------------------------------===//
805 // Check: 'vfork' should not be used.
806 // POS33-C: Do not use vfork().
807 //===----------------------------------------------------------------------===//
808 
checkCall_vfork(const CallExpr * CE,const FunctionDecl * FD)809 void WalkAST::checkCall_vfork(const CallExpr *CE, const FunctionDecl *FD) {
810   if (!filter.check_vfork)
811     return;
812 
813   // All calls to vfork() are insecure, issue a warning.
814   PathDiagnosticLocation CELoc =
815     PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
816   BR.EmitBasicReport(AC->getDecl(), filter.checkName_vfork,
817                      "Potential insecure implementation-specific behavior in "
818                      "call 'vfork'",
819                      "Security",
820                      "Call to function 'vfork' is insecure as it can lead to "
821                      "denial of service situations in the parent process. "
822                      "Replace calls to vfork with calls to the safer "
823                      "'posix_spawn' function",
824                      CELoc, CE->getCallee()->getSourceRange());
825 }
826 
827 //===----------------------------------------------------------------------===//
828 // Check: Should check whether privileges are dropped successfully.
829 // Originally: <rdar://problem/6337132>
830 //===----------------------------------------------------------------------===//
831 
checkUncheckedReturnValue(CallExpr * CE)832 void WalkAST::checkUncheckedReturnValue(CallExpr *CE) {
833   if (!filter.check_UncheckedReturn)
834     return;
835 
836   const FunctionDecl *FD = CE->getDirectCallee();
837   if (!FD)
838     return;
839 
840   if (II_setid[0] == nullptr) {
841     static const char * const identifiers[num_setids] = {
842       "setuid", "setgid", "seteuid", "setegid",
843       "setreuid", "setregid"
844     };
845 
846     for (size_t i = 0; i < num_setids; i++)
847       II_setid[i] = &BR.getContext().Idents.get(identifiers[i]);
848   }
849 
850   const IdentifierInfo *id = FD->getIdentifier();
851   size_t identifierid;
852 
853   for (identifierid = 0; identifierid < num_setids; identifierid++)
854     if (id == II_setid[identifierid])
855       break;
856 
857   if (identifierid >= num_setids)
858     return;
859 
860   const FunctionProtoType *FTP = FD->getType()->getAs<FunctionProtoType>();
861   if (!FTP)
862     return;
863 
864   // Verify that the function takes one or two arguments (depending on
865   //   the function).
866   if (FTP->getNumParams() != (identifierid < 4 ? 1 : 2))
867     return;
868 
869   // The arguments must be integers.
870   for (unsigned i = 0; i < FTP->getNumParams(); i++)
871     if (!FTP->getParamType(i)->isIntegralOrUnscopedEnumerationType())
872       return;
873 
874   // Issue a warning.
875   SmallString<256> buf1;
876   llvm::raw_svector_ostream os1(buf1);
877   os1 << "Return value is not checked in call to '" << *FD << '\'';
878 
879   SmallString<256> buf2;
880   llvm::raw_svector_ostream os2(buf2);
881   os2 << "The return value from the call to '" << *FD
882       << "' is not checked.  If an error occurs in '" << *FD
883       << "', the following code may execute with unexpected privileges";
884 
885   PathDiagnosticLocation CELoc =
886     PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
887   BR.EmitBasicReport(AC->getDecl(), filter.checkName_UncheckedReturn, os1.str(),
888                      "Security", os2.str(), CELoc,
889                      CE->getCallee()->getSourceRange());
890 }
891 
892 //===----------------------------------------------------------------------===//
893 // SecuritySyntaxChecker
894 //===----------------------------------------------------------------------===//
895 
896 namespace {
897 class SecuritySyntaxChecker : public Checker<check::ASTCodeBody> {
898 public:
899   ChecksFilter filter;
900 
checkASTCodeBody(const Decl * D,AnalysisManager & mgr,BugReporter & BR) const901   void checkASTCodeBody(const Decl *D, AnalysisManager& mgr,
902                         BugReporter &BR) const {
903     WalkAST walker(BR, mgr.getAnalysisDeclContext(D), filter);
904     walker.Visit(D->getBody());
905   }
906 };
907 }
908 
909 #define REGISTER_CHECKER(name)                                                 \
910   void ento::register##name(CheckerManager &mgr) {                             \
911     SecuritySyntaxChecker *checker =                                           \
912         mgr.registerChecker<SecuritySyntaxChecker>();                          \
913     checker->filter.check_##name = true;                                       \
914     checker->filter.checkName_##name = mgr.getCurrentCheckName();              \
915   }
916 
917 REGISTER_CHECKER(bcmp)
918 REGISTER_CHECKER(bcopy)
919 REGISTER_CHECKER(bzero)
920 REGISTER_CHECKER(gets)
921 REGISTER_CHECKER(getpw)
922 REGISTER_CHECKER(mkstemp)
923 REGISTER_CHECKER(mktemp)
924 REGISTER_CHECKER(strcpy)
925 REGISTER_CHECKER(rand)
926 REGISTER_CHECKER(vfork)
927 REGISTER_CHECKER(FloatLoopCounter)
928 REGISTER_CHECKER(UncheckedReturn)
929 
930 
931