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1 //==- CheckSecuritySyntaxOnly.cpp - Basic security checks --------*- C++ -*-==//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 //  This file defines a set of flow-insensitive security checks.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "ClangSACheckers.h"
15 #include "clang/AST/StmtVisitor.h"
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 
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.getOS() == llvm::Triple::FreeBSD ||
33          T.getOS() == llvm::Triple::NetBSD ||
34          T.getOS() == llvm::Triple::OpenBSD ||
35          T.getOS() == llvm::Triple::Bitrig ||
36          T.getOS() == llvm::Triple::DragonFly;
37 }
38 
39 namespace {
40 struct ChecksFilter {
41   DefaultBool check_gets;
42   DefaultBool check_getpw;
43   DefaultBool check_mktemp;
44   DefaultBool check_mkstemp;
45   DefaultBool check_strcpy;
46   DefaultBool check_rand;
47   DefaultBool check_vfork;
48   DefaultBool check_FloatLoopCounter;
49   DefaultBool check_UncheckedReturn;
50 
51   CheckName checkName_gets;
52   CheckName checkName_getpw;
53   CheckName checkName_mktemp;
54   CheckName checkName_mkstemp;
55   CheckName checkName_strcpy;
56   CheckName checkName_rand;
57   CheckName checkName_vfork;
58   CheckName checkName_FloatLoopCounter;
59   CheckName checkName_UncheckedReturn;
60 };
61 
62 class WalkAST : public StmtVisitor<WalkAST> {
63   BugReporter &BR;
64   AnalysisDeclContext* AC;
65   enum { num_setids = 6 };
66   IdentifierInfo *II_setid[num_setids];
67 
68   const bool CheckRand;
69   const ChecksFilter &filter;
70 
71 public:
WalkAST(BugReporter & br,AnalysisDeclContext * ac,const ChecksFilter & f)72   WalkAST(BugReporter &br, AnalysisDeclContext* ac,
73           const ChecksFilter &f)
74   : BR(br), AC(ac), II_setid(),
75     CheckRand(isArc4RandomAvailable(BR.getContext())),
76     filter(f) {}
77 
78   // Statement visitor methods.
79   void VisitCallExpr(CallExpr *CE);
80   void VisitForStmt(ForStmt *S);
81   void VisitCompoundStmt (CompoundStmt *S);
VisitStmt(Stmt * S)82   void VisitStmt(Stmt *S) { VisitChildren(S); }
83 
84   void VisitChildren(Stmt *S);
85 
86   // Helpers.
87   bool checkCall_strCommon(const CallExpr *CE, const FunctionDecl *FD);
88 
89   typedef void (WalkAST::*FnCheck)(const CallExpr *, const FunctionDecl *);
90 
91   // Checker-specific methods.
92   void checkLoopConditionForFloat(const ForStmt *FS);
93   void checkCall_gets(const CallExpr *CE, const FunctionDecl *FD);
94   void checkCall_getpw(const CallExpr *CE, const FunctionDecl *FD);
95   void checkCall_mktemp(const CallExpr *CE, const FunctionDecl *FD);
96   void checkCall_mkstemp(const CallExpr *CE, const FunctionDecl *FD);
97   void checkCall_strcpy(const CallExpr *CE, const FunctionDecl *FD);
98   void checkCall_strcat(const CallExpr *CE, const FunctionDecl *FD);
99   void checkCall_rand(const CallExpr *CE, const FunctionDecl *FD);
100   void checkCall_random(const CallExpr *CE, const FunctionDecl *FD);
101   void checkCall_vfork(const CallExpr *CE, const FunctionDecl *FD);
102   void checkUncheckedReturnValue(CallExpr *CE);
103 };
104 } // end anonymous namespace
105 
106 //===----------------------------------------------------------------------===//
107 // AST walking.
108 //===----------------------------------------------------------------------===//
109 
VisitChildren(Stmt * S)110 void WalkAST::VisitChildren(Stmt *S) {
111   for (Stmt *Child : S->children())
112     if (Child)
113       Visit(Child);
114 }
115 
VisitCallExpr(CallExpr * CE)116 void WalkAST::VisitCallExpr(CallExpr *CE) {
117   // Get the callee.
118   const FunctionDecl *FD = CE->getDirectCallee();
119 
120   if (!FD)
121     return;
122 
123   // Get the name of the callee. If it's a builtin, strip off the prefix.
124   IdentifierInfo *II = FD->getIdentifier();
125   if (!II)   // if no identifier, not a simple C function
126     return;
127   StringRef Name = II->getName();
128   if (Name.startswith("__builtin_"))
129     Name = Name.substr(10);
130 
131   // Set the evaluation function by switching on the callee name.
132   FnCheck evalFunction = llvm::StringSwitch<FnCheck>(Name)
133     .Case("gets", &WalkAST::checkCall_gets)
134     .Case("getpw", &WalkAST::checkCall_getpw)
135     .Case("mktemp", &WalkAST::checkCall_mktemp)
136     .Case("mkstemp", &WalkAST::checkCall_mkstemp)
137     .Case("mkdtemp", &WalkAST::checkCall_mkstemp)
138     .Case("mkstemps", &WalkAST::checkCall_mkstemp)
139     .Cases("strcpy", "__strcpy_chk", &WalkAST::checkCall_strcpy)
140     .Cases("strcat", "__strcat_chk", &WalkAST::checkCall_strcat)
141     .Case("drand48", &WalkAST::checkCall_rand)
142     .Case("erand48", &WalkAST::checkCall_rand)
143     .Case("jrand48", &WalkAST::checkCall_rand)
144     .Case("lrand48", &WalkAST::checkCall_rand)
145     .Case("mrand48", &WalkAST::checkCall_rand)
146     .Case("nrand48", &WalkAST::checkCall_rand)
147     .Case("lcong48", &WalkAST::checkCall_rand)
148     .Case("rand", &WalkAST::checkCall_rand)
149     .Case("rand_r", &WalkAST::checkCall_rand)
150     .Case("random", &WalkAST::checkCall_random)
151     .Case("vfork", &WalkAST::checkCall_vfork)
152     .Default(nullptr);
153 
154   // If the callee isn't defined, it is not of security concern.
155   // Check and evaluate the call.
156   if (evalFunction)
157     (this->*evalFunction)(CE, FD);
158 
159   // Recurse and check children.
160   VisitChildren(CE);
161 }
162 
VisitCompoundStmt(CompoundStmt * S)163 void WalkAST::VisitCompoundStmt(CompoundStmt *S) {
164   for (Stmt *Child : S->children())
165     if (Child) {
166       if (CallExpr *CE = dyn_cast<CallExpr>(Child))
167         checkUncheckedReturnValue(CE);
168       Visit(Child);
169     }
170 }
171 
VisitForStmt(ForStmt * FS)172 void WalkAST::VisitForStmt(ForStmt *FS) {
173   checkLoopConditionForFloat(FS);
174 
175   // Recurse and check children.
176   VisitChildren(FS);
177 }
178 
179 //===----------------------------------------------------------------------===//
180 // Check: floating poing variable used as loop counter.
181 // Originally: <rdar://problem/6336718>
182 // Implements: CERT security coding advisory FLP-30.
183 //===----------------------------------------------------------------------===//
184 
185 static const DeclRefExpr*
getIncrementedVar(const Expr * expr,const VarDecl * x,const VarDecl * y)186 getIncrementedVar(const Expr *expr, const VarDecl *x, const VarDecl *y) {
187   expr = expr->IgnoreParenCasts();
188 
189   if (const BinaryOperator *B = dyn_cast<BinaryOperator>(expr)) {
190     if (!(B->isAssignmentOp() || B->isCompoundAssignmentOp() ||
191           B->getOpcode() == BO_Comma))
192       return nullptr;
193 
194     if (const DeclRefExpr *lhs = getIncrementedVar(B->getLHS(), x, y))
195       return lhs;
196 
197     if (const DeclRefExpr *rhs = getIncrementedVar(B->getRHS(), x, y))
198       return rhs;
199 
200     return nullptr;
201   }
202 
203   if (const DeclRefExpr *DR = dyn_cast<DeclRefExpr>(expr)) {
204     const NamedDecl *ND = DR->getDecl();
205     return ND == x || ND == y ? DR : nullptr;
206   }
207 
208   if (const UnaryOperator *U = dyn_cast<UnaryOperator>(expr))
209     return U->isIncrementDecrementOp()
210       ? getIncrementedVar(U->getSubExpr(), x, y) : nullptr;
211 
212   return nullptr;
213 }
214 
215 /// CheckLoopConditionForFloat - This check looks for 'for' statements that
216 ///  use a floating point variable as a loop counter.
217 ///  CERT: FLP30-C, FLP30-CPP.
218 ///
checkLoopConditionForFloat(const ForStmt * FS)219 void WalkAST::checkLoopConditionForFloat(const ForStmt *FS) {
220   if (!filter.check_FloatLoopCounter)
221     return;
222 
223   // Does the loop have a condition?
224   const Expr *condition = FS->getCond();
225 
226   if (!condition)
227     return;
228 
229   // Does the loop have an increment?
230   const Expr *increment = FS->getInc();
231 
232   if (!increment)
233     return;
234 
235   // Strip away '()' and casts.
236   condition = condition->IgnoreParenCasts();
237   increment = increment->IgnoreParenCasts();
238 
239   // Is the loop condition a comparison?
240   const BinaryOperator *B = dyn_cast<BinaryOperator>(condition);
241 
242   if (!B)
243     return;
244 
245   // Is this a comparison?
246   if (!(B->isRelationalOp() || B->isEqualityOp()))
247     return;
248 
249   // Are we comparing variables?
250   const DeclRefExpr *drLHS =
251     dyn_cast<DeclRefExpr>(B->getLHS()->IgnoreParenLValueCasts());
252   const DeclRefExpr *drRHS =
253     dyn_cast<DeclRefExpr>(B->getRHS()->IgnoreParenLValueCasts());
254 
255   // Does at least one of the variables have a floating point type?
256   drLHS = drLHS && drLHS->getType()->isRealFloatingType() ? drLHS : nullptr;
257   drRHS = drRHS && drRHS->getType()->isRealFloatingType() ? drRHS : nullptr;
258 
259   if (!drLHS && !drRHS)
260     return;
261 
262   const VarDecl *vdLHS = drLHS ? dyn_cast<VarDecl>(drLHS->getDecl()) : nullptr;
263   const VarDecl *vdRHS = drRHS ? dyn_cast<VarDecl>(drRHS->getDecl()) : nullptr;
264 
265   if (!vdLHS && !vdRHS)
266     return;
267 
268   // Does either variable appear in increment?
269   const DeclRefExpr *drInc = getIncrementedVar(increment, vdLHS, vdRHS);
270 
271   if (!drInc)
272     return;
273 
274   // Emit the error.  First figure out which DeclRefExpr in the condition
275   // referenced the compared variable.
276   assert(drInc->getDecl());
277   const DeclRefExpr *drCond = vdLHS == drInc->getDecl() ? drLHS : drRHS;
278 
279   SmallVector<SourceRange, 2> ranges;
280   SmallString<256> sbuf;
281   llvm::raw_svector_ostream os(sbuf);
282 
283   os << "Variable '" << drCond->getDecl()->getName()
284      << "' with floating point type '" << drCond->getType().getAsString()
285      << "' should not be used as a loop counter";
286 
287   ranges.push_back(drCond->getSourceRange());
288   ranges.push_back(drInc->getSourceRange());
289 
290   const char *bugType = "Floating point variable used as loop counter";
291 
292   PathDiagnosticLocation FSLoc =
293     PathDiagnosticLocation::createBegin(FS, BR.getSourceManager(), AC);
294   BR.EmitBasicReport(AC->getDecl(), filter.checkName_FloatLoopCounter,
295                      bugType, "Security", os.str(),
296                      FSLoc, ranges);
297 }
298 
299 //===----------------------------------------------------------------------===//
300 // Check: Any use of 'gets' is insecure.
301 // Originally: <rdar://problem/6335715>
302 // Implements (part of): 300-BSI (buildsecurityin.us-cert.gov)
303 // CWE-242: Use of Inherently Dangerous Function
304 //===----------------------------------------------------------------------===//
305 
checkCall_gets(const CallExpr * CE,const FunctionDecl * FD)306 void WalkAST::checkCall_gets(const CallExpr *CE, const FunctionDecl *FD) {
307   if (!filter.check_gets)
308     return;
309 
310   const FunctionProtoType *FPT = FD->getType()->getAs<FunctionProtoType>();
311   if (!FPT)
312     return;
313 
314   // Verify that the function takes a single argument.
315   if (FPT->getNumParams() != 1)
316     return;
317 
318   // Is the argument a 'char*'?
319   const PointerType *PT = FPT->getParamType(0)->getAs<PointerType>();
320   if (!PT)
321     return;
322 
323   if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
324     return;
325 
326   // Issue a warning.
327   PathDiagnosticLocation CELoc =
328     PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
329   BR.EmitBasicReport(AC->getDecl(), filter.checkName_gets,
330                      "Potential buffer overflow in call to 'gets'",
331                      "Security",
332                      "Call to function 'gets' is extremely insecure as it can "
333                      "always result in a buffer overflow",
334                      CELoc, CE->getCallee()->getSourceRange());
335 }
336 
337 //===----------------------------------------------------------------------===//
338 // Check: Any use of 'getpwd' is insecure.
339 // CWE-477: Use of Obsolete Functions
340 //===----------------------------------------------------------------------===//
341 
checkCall_getpw(const CallExpr * CE,const FunctionDecl * FD)342 void WalkAST::checkCall_getpw(const CallExpr *CE, const FunctionDecl *FD) {
343   if (!filter.check_getpw)
344     return;
345 
346   const FunctionProtoType *FPT = FD->getType()->getAs<FunctionProtoType>();
347   if (!FPT)
348     return;
349 
350   // Verify that the function takes two arguments.
351   if (FPT->getNumParams() != 2)
352     return;
353 
354   // Verify the first argument type is integer.
355   if (!FPT->getParamType(0)->isIntegralOrUnscopedEnumerationType())
356     return;
357 
358   // Verify the second argument type is char*.
359   const PointerType *PT = FPT->getParamType(1)->getAs<PointerType>();
360   if (!PT)
361     return;
362 
363   if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
364     return;
365 
366   // Issue a warning.
367   PathDiagnosticLocation CELoc =
368     PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
369   BR.EmitBasicReport(AC->getDecl(), filter.checkName_getpw,
370                      "Potential buffer overflow in call to 'getpw'",
371                      "Security",
372                      "The getpw() function is dangerous as it may overflow the "
373                      "provided buffer. It is obsoleted by getpwuid().",
374                      CELoc, CE->getCallee()->getSourceRange());
375 }
376 
377 //===----------------------------------------------------------------------===//
378 // Check: Any use of 'mktemp' is insecure.  It is obsoleted by mkstemp().
379 // CWE-377: Insecure Temporary File
380 //===----------------------------------------------------------------------===//
381 
checkCall_mktemp(const CallExpr * CE,const FunctionDecl * FD)382 void WalkAST::checkCall_mktemp(const CallExpr *CE, const FunctionDecl *FD) {
383   if (!filter.check_mktemp) {
384     // Fall back to the security check of looking for enough 'X's in the
385     // format string, since that is a less severe warning.
386     checkCall_mkstemp(CE, FD);
387     return;
388   }
389 
390   const FunctionProtoType *FPT = FD->getType()->getAs<FunctionProtoType>();
391   if(!FPT)
392     return;
393 
394   // Verify that the function takes a single argument.
395   if (FPT->getNumParams() != 1)
396     return;
397 
398   // Verify that the argument is Pointer Type.
399   const PointerType *PT = FPT->getParamType(0)->getAs<PointerType>();
400   if (!PT)
401     return;
402 
403   // Verify that the argument is a 'char*'.
404   if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
405     return;
406 
407   // Issue a warning.
408   PathDiagnosticLocation CELoc =
409     PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
410   BR.EmitBasicReport(AC->getDecl(), filter.checkName_mktemp,
411                      "Potential insecure temporary file in call 'mktemp'",
412                      "Security",
413                      "Call to function 'mktemp' is insecure as it always "
414                      "creates or uses insecure temporary file.  Use 'mkstemp' "
415                      "instead",
416                      CELoc, CE->getCallee()->getSourceRange());
417 }
418 
419 
420 //===----------------------------------------------------------------------===//
421 // Check: Use of 'mkstemp', 'mktemp', 'mkdtemp' should contain at least 6 X's.
422 //===----------------------------------------------------------------------===//
423 
checkCall_mkstemp(const CallExpr * CE,const FunctionDecl * FD)424 void WalkAST::checkCall_mkstemp(const CallExpr *CE, const FunctionDecl *FD) {
425   if (!filter.check_mkstemp)
426     return;
427 
428   StringRef Name = FD->getIdentifier()->getName();
429   std::pair<signed, signed> ArgSuffix =
430     llvm::StringSwitch<std::pair<signed, signed> >(Name)
431       .Case("mktemp", std::make_pair(0,-1))
432       .Case("mkstemp", std::make_pair(0,-1))
433       .Case("mkdtemp", std::make_pair(0,-1))
434       .Case("mkstemps", std::make_pair(0,1))
435       .Default(std::make_pair(-1, -1));
436 
437   assert(ArgSuffix.first >= 0 && "Unsupported function");
438 
439   // Check if the number of arguments is consistent with out expectations.
440   unsigned numArgs = CE->getNumArgs();
441   if ((signed) numArgs <= ArgSuffix.first)
442     return;
443 
444   const StringLiteral *strArg =
445     dyn_cast<StringLiteral>(CE->getArg((unsigned)ArgSuffix.first)
446                               ->IgnoreParenImpCasts());
447 
448   // Currently we only handle string literals.  It is possible to do better,
449   // either by looking at references to const variables, or by doing real
450   // flow analysis.
451   if (!strArg || strArg->getCharByteWidth() != 1)
452     return;
453 
454   // Count the number of X's, taking into account a possible cutoff suffix.
455   StringRef str = strArg->getString();
456   unsigned numX = 0;
457   unsigned n = str.size();
458 
459   // Take into account the suffix.
460   unsigned suffix = 0;
461   if (ArgSuffix.second >= 0) {
462     const Expr *suffixEx = CE->getArg((unsigned)ArgSuffix.second);
463     llvm::APSInt Result;
464     if (!suffixEx->EvaluateAsInt(Result, BR.getContext()))
465       return;
466     // FIXME: Issue a warning.
467     if (Result.isNegative())
468       return;
469     suffix = (unsigned) Result.getZExtValue();
470     n = (n > suffix) ? n - suffix : 0;
471   }
472 
473   for (unsigned i = 0; i < n; ++i)
474     if (str[i] == 'X') ++numX;
475 
476   if (numX >= 6)
477     return;
478 
479   // Issue a warning.
480   PathDiagnosticLocation CELoc =
481     PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
482   SmallString<512> buf;
483   llvm::raw_svector_ostream out(buf);
484   out << "Call to '" << Name << "' should have at least 6 'X's in the"
485     " format string to be secure (" << numX << " 'X'";
486   if (numX != 1)
487     out << 's';
488   out << " seen";
489   if (suffix) {
490     out << ", " << suffix << " character";
491     if (suffix > 1)
492       out << 's';
493     out << " used as a suffix";
494   }
495   out << ')';
496   BR.EmitBasicReport(AC->getDecl(), filter.checkName_mkstemp,
497                      "Insecure temporary file creation", "Security",
498                      out.str(), CELoc, strArg->getSourceRange());
499 }
500 
501 //===----------------------------------------------------------------------===//
502 // Check: Any use of 'strcpy' is insecure.
503 //
504 // CWE-119: Improper Restriction of Operations within
505 // the Bounds of a Memory Buffer
506 //===----------------------------------------------------------------------===//
checkCall_strcpy(const CallExpr * CE,const FunctionDecl * FD)507 void WalkAST::checkCall_strcpy(const CallExpr *CE, const FunctionDecl *FD) {
508   if (!filter.check_strcpy)
509     return;
510 
511   if (!checkCall_strCommon(CE, FD))
512     return;
513 
514   // Issue a warning.
515   PathDiagnosticLocation CELoc =
516     PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
517   BR.EmitBasicReport(AC->getDecl(), filter.checkName_strcpy,
518                      "Potential insecure memory buffer bounds restriction in "
519                      "call 'strcpy'",
520                      "Security",
521                      "Call to function 'strcpy' is insecure as it does not "
522                      "provide bounding of the memory buffer. Replace "
523                      "unbounded copy functions with analogous functions that "
524                      "support length arguments such as 'strlcpy'. CWE-119.",
525                      CELoc, CE->getCallee()->getSourceRange());
526 }
527 
528 //===----------------------------------------------------------------------===//
529 // Check: Any use of 'strcat' is insecure.
530 //
531 // CWE-119: Improper Restriction of Operations within
532 // the Bounds of a Memory Buffer
533 //===----------------------------------------------------------------------===//
checkCall_strcat(const CallExpr * CE,const FunctionDecl * FD)534 void WalkAST::checkCall_strcat(const CallExpr *CE, const FunctionDecl *FD) {
535   if (!filter.check_strcpy)
536     return;
537 
538   if (!checkCall_strCommon(CE, FD))
539     return;
540 
541   // Issue a warning.
542   PathDiagnosticLocation CELoc =
543     PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
544   BR.EmitBasicReport(AC->getDecl(), filter.checkName_strcpy,
545                      "Potential insecure memory buffer bounds restriction in "
546                      "call 'strcat'",
547                      "Security",
548                      "Call to function 'strcat' is insecure as it does not "
549                      "provide bounding of the memory buffer. Replace "
550                      "unbounded copy functions with analogous functions that "
551                      "support length arguments such as 'strlcat'. CWE-119.",
552                      CELoc, CE->getCallee()->getSourceRange());
553 }
554 
555 //===----------------------------------------------------------------------===//
556 // Common check for str* functions with no bounds parameters.
557 //===----------------------------------------------------------------------===//
checkCall_strCommon(const CallExpr * CE,const FunctionDecl * FD)558 bool WalkAST::checkCall_strCommon(const CallExpr *CE, const FunctionDecl *FD) {
559   const FunctionProtoType *FPT = FD->getType()->getAs<FunctionProtoType>();
560   if (!FPT)
561     return false;
562 
563   // Verify the function takes two arguments, three in the _chk version.
564   int numArgs = FPT->getNumParams();
565   if (numArgs != 2 && numArgs != 3)
566     return false;
567 
568   // Verify the type for both arguments.
569   for (int i = 0; i < 2; i++) {
570     // Verify that the arguments are pointers.
571     const PointerType *PT = FPT->getParamType(i)->getAs<PointerType>();
572     if (!PT)
573       return false;
574 
575     // Verify that the argument is a 'char*'.
576     if (PT->getPointeeType().getUnqualifiedType() != BR.getContext().CharTy)
577       return false;
578   }
579 
580   return true;
581 }
582 
583 //===----------------------------------------------------------------------===//
584 // Check: Linear congruent random number generators should not be used
585 // Originally: <rdar://problem/63371000>
586 // CWE-338: Use of cryptographically weak prng
587 //===----------------------------------------------------------------------===//
588 
checkCall_rand(const CallExpr * CE,const FunctionDecl * FD)589 void WalkAST::checkCall_rand(const CallExpr *CE, const FunctionDecl *FD) {
590   if (!filter.check_rand || !CheckRand)
591     return;
592 
593   const FunctionProtoType *FTP = FD->getType()->getAs<FunctionProtoType>();
594   if (!FTP)
595     return;
596 
597   if (FTP->getNumParams() == 1) {
598     // Is the argument an 'unsigned short *'?
599     // (Actually any integer type is allowed.)
600     const PointerType *PT = FTP->getParamType(0)->getAs<PointerType>();
601     if (!PT)
602       return;
603 
604     if (! PT->getPointeeType()->isIntegralOrUnscopedEnumerationType())
605       return;
606   } else if (FTP->getNumParams() != 0)
607     return;
608 
609   // Issue a warning.
610   SmallString<256> buf1;
611   llvm::raw_svector_ostream os1(buf1);
612   os1 << '\'' << *FD << "' is a poor random number generator";
613 
614   SmallString<256> buf2;
615   llvm::raw_svector_ostream os2(buf2);
616   os2 << "Function '" << *FD
617       << "' is obsolete because it implements a poor random number generator."
618       << "  Use 'arc4random' instead";
619 
620   PathDiagnosticLocation CELoc =
621     PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
622   BR.EmitBasicReport(AC->getDecl(), filter.checkName_rand, os1.str(),
623                      "Security", os2.str(), CELoc,
624                      CE->getCallee()->getSourceRange());
625 }
626 
627 //===----------------------------------------------------------------------===//
628 // Check: 'random' should not be used
629 // Originally: <rdar://problem/63371000>
630 //===----------------------------------------------------------------------===//
631 
checkCall_random(const CallExpr * CE,const FunctionDecl * FD)632 void WalkAST::checkCall_random(const CallExpr *CE, const FunctionDecl *FD) {
633   if (!CheckRand || !filter.check_rand)
634     return;
635 
636   const FunctionProtoType *FTP = FD->getType()->getAs<FunctionProtoType>();
637   if (!FTP)
638     return;
639 
640   // Verify that the function takes no argument.
641   if (FTP->getNumParams() != 0)
642     return;
643 
644   // Issue a warning.
645   PathDiagnosticLocation CELoc =
646     PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
647   BR.EmitBasicReport(AC->getDecl(), filter.checkName_rand,
648                      "'random' is not a secure random number generator",
649                      "Security",
650                      "The 'random' function produces a sequence of values that "
651                      "an adversary may be able to predict.  Use 'arc4random' "
652                      "instead", CELoc, CE->getCallee()->getSourceRange());
653 }
654 
655 //===----------------------------------------------------------------------===//
656 // Check: 'vfork' should not be used.
657 // POS33-C: Do not use vfork().
658 //===----------------------------------------------------------------------===//
659 
checkCall_vfork(const CallExpr * CE,const FunctionDecl * FD)660 void WalkAST::checkCall_vfork(const CallExpr *CE, const FunctionDecl *FD) {
661   if (!filter.check_vfork)
662     return;
663 
664   // All calls to vfork() are insecure, issue a warning.
665   PathDiagnosticLocation CELoc =
666     PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
667   BR.EmitBasicReport(AC->getDecl(), filter.checkName_vfork,
668                      "Potential insecure implementation-specific behavior in "
669                      "call 'vfork'",
670                      "Security",
671                      "Call to function 'vfork' is insecure as it can lead to "
672                      "denial of service situations in the parent process. "
673                      "Replace calls to vfork with calls to the safer "
674                      "'posix_spawn' function",
675                      CELoc, CE->getCallee()->getSourceRange());
676 }
677 
678 //===----------------------------------------------------------------------===//
679 // Check: Should check whether privileges are dropped successfully.
680 // Originally: <rdar://problem/6337132>
681 //===----------------------------------------------------------------------===//
682 
checkUncheckedReturnValue(CallExpr * CE)683 void WalkAST::checkUncheckedReturnValue(CallExpr *CE) {
684   if (!filter.check_UncheckedReturn)
685     return;
686 
687   const FunctionDecl *FD = CE->getDirectCallee();
688   if (!FD)
689     return;
690 
691   if (II_setid[0] == nullptr) {
692     static const char * const identifiers[num_setids] = {
693       "setuid", "setgid", "seteuid", "setegid",
694       "setreuid", "setregid"
695     };
696 
697     for (size_t i = 0; i < num_setids; i++)
698       II_setid[i] = &BR.getContext().Idents.get(identifiers[i]);
699   }
700 
701   const IdentifierInfo *id = FD->getIdentifier();
702   size_t identifierid;
703 
704   for (identifierid = 0; identifierid < num_setids; identifierid++)
705     if (id == II_setid[identifierid])
706       break;
707 
708   if (identifierid >= num_setids)
709     return;
710 
711   const FunctionProtoType *FTP = FD->getType()->getAs<FunctionProtoType>();
712   if (!FTP)
713     return;
714 
715   // Verify that the function takes one or two arguments (depending on
716   //   the function).
717   if (FTP->getNumParams() != (identifierid < 4 ? 1 : 2))
718     return;
719 
720   // The arguments must be integers.
721   for (unsigned i = 0; i < FTP->getNumParams(); i++)
722     if (!FTP->getParamType(i)->isIntegralOrUnscopedEnumerationType())
723       return;
724 
725   // Issue a warning.
726   SmallString<256> buf1;
727   llvm::raw_svector_ostream os1(buf1);
728   os1 << "Return value is not checked in call to '" << *FD << '\'';
729 
730   SmallString<256> buf2;
731   llvm::raw_svector_ostream os2(buf2);
732   os2 << "The return value from the call to '" << *FD
733       << "' is not checked.  If an error occurs in '" << *FD
734       << "', the following code may execute with unexpected privileges";
735 
736   PathDiagnosticLocation CELoc =
737     PathDiagnosticLocation::createBegin(CE, BR.getSourceManager(), AC);
738   BR.EmitBasicReport(AC->getDecl(), filter.checkName_UncheckedReturn, os1.str(),
739                      "Security", os2.str(), CELoc,
740                      CE->getCallee()->getSourceRange());
741 }
742 
743 //===----------------------------------------------------------------------===//
744 // SecuritySyntaxChecker
745 //===----------------------------------------------------------------------===//
746 
747 namespace {
748 class SecuritySyntaxChecker : public Checker<check::ASTCodeBody> {
749 public:
750   ChecksFilter filter;
751 
checkASTCodeBody(const Decl * D,AnalysisManager & mgr,BugReporter & BR) const752   void checkASTCodeBody(const Decl *D, AnalysisManager& mgr,
753                         BugReporter &BR) const {
754     WalkAST walker(BR, mgr.getAnalysisDeclContext(D), filter);
755     walker.Visit(D->getBody());
756   }
757 };
758 }
759 
760 #define REGISTER_CHECKER(name)                                                 \
761   void ento::register##name(CheckerManager &mgr) {                             \
762     SecuritySyntaxChecker *checker =                                           \
763         mgr.registerChecker<SecuritySyntaxChecker>();                          \
764     checker->filter.check_##name = true;                                       \
765     checker->filter.checkName_##name = mgr.getCurrentCheckName();              \
766   }
767 
768 REGISTER_CHECKER(gets)
769 REGISTER_CHECKER(getpw)
770 REGISTER_CHECKER(mkstemp)
771 REGISTER_CHECKER(mktemp)
772 REGISTER_CHECKER(strcpy)
773 REGISTER_CHECKER(rand)
774 REGISTER_CHECKER(vfork)
775 REGISTER_CHECKER(FloatLoopCounter)
776 REGISTER_CHECKER(UncheckedReturn)
777 
778 
779