text: //= UnixAPIChecker.h - Checks preconditions for various Unix APIs --*- C++ -*-//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // This defines UnixAPIChecker, which is an assortment of checks on calls
  // to various, widely used UNIX/Posix functions.
  //
  //===----------------------------------------------------------------------===//
  
  #include "ClangSACheckers.h"
  #include "clang/StaticAnalyzer/Core/Checker.h"
  #include "clang/StaticAnalyzer/Core/CheckerManager.h"
  #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
  #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
  #include "clang/Basic/TargetInfo.h"
  #include "llvm/ADT/Optional.h"
  #include "llvm/ADT/SmallString.h"
  #include "llvm/ADT/STLExtras.h"
  #include "llvm/ADT/StringSwitch.h"
  #include <fcntl.h>
  
  using namespace clang;
  using namespace ento;
  using llvm::Optional;
  
  namespace {
  class UnixAPIChecker : public Checker< check::PreStmt<CallExpr> > {
    mutable OwningPtr<BugType> BT_open, BT_pthreadOnce, BT_mallocZero;
    mutable Optional<uint64_t> Val_O_CREAT;
  
  public:
    void checkPreStmt(const CallExpr *CE, CheckerContext &C) const;
  
    void CheckOpen(CheckerContext &C, const CallExpr *CE) const;
    void CheckPthreadOnce(CheckerContext &C, const CallExpr *CE) const;
    void CheckCallocZero(CheckerContext &C, const CallExpr *CE) const;
    void CheckMallocZero(CheckerContext &C, const CallExpr *CE) const;
    void CheckReallocZero(CheckerContext &C, const CallExpr *CE) const;
    void CheckAllocaZero(CheckerContext &C, const CallExpr *CE) const;
    void CheckVallocZero(CheckerContext &C, const CallExpr *CE) const;
  
    typedef void (UnixAPIChecker::*SubChecker)(CheckerContext &,
                                               const CallExpr *) const;
  private:
    bool ReportZeroByteAllocation(CheckerContext &C,
                                  ProgramStateRef falseState,
                                  const Expr *arg,
                                  const char *fn_name) const;
    void BasicAllocationCheck(CheckerContext &C,
                              const CallExpr *CE,
                              const unsigned numArgs,
                              const unsigned sizeArg,
                              const char *fn) const;
  };
  } //end anonymous namespace
  
  //===----------------------------------------------------------------------===//
  // Utility functions.
  //===----------------------------------------------------------------------===//
  
  static inline void LazyInitialize(OwningPtr<BugType> &BT,
                                    const char *name) {
    if (BT)
      return;
    BT.reset(new BugType(name, categories::UnixAPI));
  }
  
  //===----------------------------------------------------------------------===//
  // "open" (man 2 open)
  //===----------------------------------------------------------------------===//
  
  void UnixAPIChecker::CheckOpen(CheckerContext &C, const CallExpr *CE) const {
    // The definition of O_CREAT is platform specific.  We need a better way
    // of querying this information from the checking environment.
    if (!Val_O_CREAT.hasValue()) {
      if (C.getASTContext().getTargetInfo().getTriple().getVendor() 
                                                        == llvm::Triple::Apple)
        Val_O_CREAT = 0x0200;
      else {
        // FIXME: We need a more general way of getting the O_CREAT value.
        // We could possibly grovel through the preprocessor state, but
        // that would require passing the Preprocessor object to the ExprEngine.
        return;
      }
    }
  
    // Look at the 'oflags' argument for the O_CREAT flag.
    ProgramStateRef state = C.getState();
  
    if (CE->getNumArgs() < 2) {
      // The frontend should issue a warning for this case, so this is a sanity
      // check.
      return;
    }
  
    // Now check if oflags has O_CREAT set.
    const Expr *oflagsEx = CE->getArg(1);
    const SVal V = state->getSVal(oflagsEx, C.getLocationContext());
    if (!isa<NonLoc>(V)) {
      // The case where 'V' can be a location can only be due to a bad header,
      // so in this case bail out.
      return;
    }
    NonLoc oflags = cast<NonLoc>(V);
    NonLoc ocreateFlag =
      cast<NonLoc>(C.getSValBuilder().makeIntVal(Val_O_CREAT.getValue(),
                                                  oflagsEx->getType()));
    SVal maskedFlagsUC = C.getSValBuilder().evalBinOpNN(state, BO_And,
                                                        oflags, ocreateFlag,
                                                        oflagsEx->getType());
    if (maskedFlagsUC.isUnknownOrUndef())
      return;
    DefinedSVal maskedFlags = cast<DefinedSVal>(maskedFlagsUC);
  
    // Check if maskedFlags is non-zero.
    ProgramStateRef trueState, falseState;
    llvm::tie(trueState, falseState) = state->assume(maskedFlags);
  
    // Only emit an error if the value of 'maskedFlags' is properly
    // constrained;
    if (!(trueState && !falseState))
      return;
  
    if (CE->getNumArgs() < 3) {
      ExplodedNode *N = C.generateSink(trueState);
      if (!N)
        return;
  
      LazyInitialize(BT_open, "Improper use of 'open'");
  
      BugReport *report =
        new BugReport(*BT_open,
                              "Call to 'open' requires a third argument when "
                              "the 'O_CREAT' flag is set", N);
      report->addRange(oflagsEx->getSourceRange());
      C.EmitReport(report);
    }
  }
  
  //===----------------------------------------------------------------------===//
  // pthread_once
  //===----------------------------------------------------------------------===//
  
  void UnixAPIChecker::CheckPthreadOnce(CheckerContext &C,
                                        const CallExpr *CE) const {
  
    // This is similar to 'CheckDispatchOnce' in the MacOSXAPIChecker.
    // They can possibly be refactored.
  
    if (CE->getNumArgs() < 1)
      return;
  
    // Check if the first argument is stack allocated.  If so, issue a warning
    // because that's likely to be bad news.
    ProgramStateRef state = C.getState();
    const MemRegion *R =
      state->getSVal(CE->getArg(0), C.getLocationContext()).getAsRegion();
    if (!R || !isa<StackSpaceRegion>(R->getMemorySpace()))
      return;
  
    ExplodedNode *N = C.generateSink(state);
    if (!N)
      return;
  
    SmallString<256> S;
    llvm::raw_svector_ostream os(S);
    os << "Call to 'pthread_once' uses";
    if (const VarRegion *VR = dyn_cast<VarRegion>(R))
      os << " the local variable '" << VR->getDecl()->getName() << '\'';
    else
      os << " stack allocated memory";
    os << " for the \"control\" value.  Using such transient memory for "
    "the control value is potentially dangerous.";
    if (isa<VarRegion>(R) && isa<StackLocalsSpaceRegion>(R->getMemorySpace()))
      os << "  Perhaps you intended to declare the variable as 'static'?";
  
    LazyInitialize(BT_pthreadOnce, "Improper use of 'pthread_once'");
  
    BugReport *report = new BugReport(*BT_pthreadOnce, os.str(), N);
    report->addRange(CE->getArg(0)->getSourceRange());
    C.EmitReport(report);
  }
  
  //===----------------------------------------------------------------------===//
  // "calloc", "malloc", "realloc", "alloca" and "valloc" with allocation size 0
  //===----------------------------------------------------------------------===//
  // FIXME: Eventually these should be rolled into the MallocChecker, but right now
  // they're more basic and valuable for widespread use.
  
  // Returns true if we try to do a zero byte allocation, false otherwise.
  // Fills in trueState and falseState.
  static bool IsZeroByteAllocation(ProgramStateRef state,
                                  const SVal argVal,
                                  ProgramStateRef *trueState,
                                  ProgramStateRef *falseState) {
    llvm::tie(*trueState, *falseState) =
      state->assume(cast<DefinedSVal>(argVal));
    
    return (*falseState && !*trueState);
  }
  
  // Generates an error report, indicating that the function whose name is given
  // will perform a zero byte allocation.
  // Returns false if an error occured, true otherwise.
  bool UnixAPIChecker::ReportZeroByteAllocation(CheckerContext &C,
                                                ProgramStateRef falseState,
                                                const Expr *arg,
                                                const char *fn_name) const {
    ExplodedNode *N = C.generateSink(falseState);
    if (!N)
      return false;
  
    LazyInitialize(BT_mallocZero,
      "Undefined allocation of 0 bytes (CERT MEM04-C; CWE-131)");
  
    SmallString<256> S;
    llvm::raw_svector_ostream os(S);    
    os << "Call to '" << fn_name << "' has an allocation size of 0 bytes";
    BugReport *report = new BugReport(*BT_mallocZero, os.str(), N);
  
    report->addRange(arg->getSourceRange());
    bugreporter::trackNullOrUndefValue(N, arg, *report);
    C.EmitReport(report);
  
    return true;
  }
  
  // Does a basic check for 0-sized allocations suitable for most of the below
  // functions (modulo "calloc")
  void UnixAPIChecker::BasicAllocationCheck(CheckerContext &C,
                                            const CallExpr *CE,
                                            const unsigned numArgs,
                                            const unsigned sizeArg,
                                            const char *fn) const {
    // Sanity check for the correct number of arguments
    if (CE->getNumArgs() != numArgs)
      return;
  
    // Check if the allocation size is 0.
    ProgramStateRef state = C.getState();
    ProgramStateRef trueState = NULL, falseState = NULL;
    const Expr *arg = CE->getArg(sizeArg);
    SVal argVal = state->getSVal(arg, C.getLocationContext());
  
    if (argVal.isUnknownOrUndef())
      return;
  
    // Is the value perfectly constrained to zero?
    if (IsZeroByteAllocation(state, argVal, &trueState, &falseState)) {
      (void) ReportZeroByteAllocation(C, falseState, arg, fn); 
      return;
    }
    // Assume the value is non-zero going forward.
    assert(trueState);
    if (trueState != state)
      C.addTransition(trueState);                           
  }
  
  void UnixAPIChecker::CheckCallocZero(CheckerContext &C,
                                       const CallExpr *CE) const {
    unsigned int nArgs = CE->getNumArgs();
    if (nArgs != 2)
      return;
  
    ProgramStateRef state = C.getState();
    ProgramStateRef trueState = NULL, falseState = NULL;
  
    unsigned int i;
    for (i = 0; i < nArgs; i++) {
      const Expr *arg = CE->getArg(i);
      SVal argVal = state->getSVal(arg, C.getLocationContext());
      if (argVal.isUnknownOrUndef()) {
        if (i == 0)
          continue;
        else
          return;
      }
  
      if (IsZeroByteAllocation(state, argVal, &trueState, &falseState)) {
        if (ReportZeroByteAllocation(C, falseState, arg, "calloc"))
          return;
        else if (i == 0)
          continue;
        else
          return;
      }
    }
  
    // Assume the value is non-zero going forward.
    assert(trueState);
    if (trueState != state)
      C.addTransition(trueState);
  }
  
  void UnixAPIChecker::CheckMallocZero(CheckerContext &C,
                                       const CallExpr *CE) const {
    BasicAllocationCheck(C, CE, 1, 0, "malloc");
  }
  
  void UnixAPIChecker::CheckReallocZero(CheckerContext &C,
                                        const CallExpr *CE) const {
    BasicAllocationCheck(C, CE, 2, 1, "realloc");
  }
  
  void UnixAPIChecker::CheckAllocaZero(CheckerContext &C,
                                       const CallExpr *CE) const {
    BasicAllocationCheck(C, CE, 1, 0, "alloca");
  }
  
  void UnixAPIChecker::CheckVallocZero(CheckerContext &C,
                                       const CallExpr *CE) const {
    BasicAllocationCheck(C, CE, 1, 0, "valloc");
  }
  
  
  //===----------------------------------------------------------------------===//
  // Central dispatch function.
  //===----------------------------------------------------------------------===//
  
  void UnixAPIChecker::checkPreStmt(const CallExpr *CE,
                                    CheckerContext &C) const {
    const FunctionDecl *FD = C.getCalleeDecl(CE);
    if (!FD || FD->getKind() != Decl::Function)
      return;
  
    StringRef FName = C.getCalleeName(FD);
    if (FName.empty())
      return;
  
    SubChecker SC =
      llvm::StringSwitch<SubChecker>(FName)
        .Case("open", &UnixAPIChecker::CheckOpen)
        .Case("pthread_once", &UnixAPIChecker::CheckPthreadOnce)
        .Case("calloc", &UnixAPIChecker::CheckCallocZero)
        .Case("malloc", &UnixAPIChecker::CheckMallocZero)
        .Case("realloc", &UnixAPIChecker::CheckReallocZero)
        .Cases("alloca", "__builtin_alloca", &UnixAPIChecker::CheckAllocaZero)
        .Case("valloc", &UnixAPIChecker::CheckVallocZero)
        .Default(NULL);
  
    if (SC)
      (this->*SC)(C, CE);
  }
  
  //===----------------------------------------------------------------------===//
  // Registration.
  //===----------------------------------------------------------------------===//
  
  void ento::registerUnixAPIChecker(CheckerManager &mgr) {
    mgr.registerChecker<UnixAPIChecker>();
  }
  