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