dbus/file_descriptor.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef DBUS_FILE_DESCRIPTOR_H_
   6 #define DBUS_FILE_DESCRIPTOR_H_
   7
   8 #include "base/basictypes.h"
   9 #include "dbus/dbus_export.h"
  10
  11 namespace dbus {
  12
  13 // FileDescriptor is a type used to encapsulate D-Bus file descriptors
  14 // and to follow the RAII idiom appropiate for use with message operations
  15 // where the descriptor might be easily leaked.  To guard against this the
  16 // descriptor is closed when an instance is destroyed if it is owned.
  17 // Ownership is asserted only when PutValue is used and TakeValue can be
  18 // used to take ownership.
  19 //
  20 // For example, in the following
  21 //  FileDescriptor fd;
  22 //  if (!reader->PopString(&name) ||
  23 //      !reader->PopFileDescriptor(&fd) ||
  24 //      !reader->PopUint32(&flags)) {
  25 // the descriptor in fd will be closed if the PopUint32 fails.  But
  26 //   writer.AppendFileDescriptor(dbus::FileDescriptor(1));
  27 // will not automatically close "1" because it is not owned.
  28 //
  29 // Descriptors must be validated before marshalling in a D-Bus message
  30 // or using them after unmarshalling.  We disallow descriptors to a
  31 // directory to reduce the security risks.  Splitting out validation
  32 // also allows the caller to do this work on the File thread to conform
  33 // with i/o restrictions.
  34 class CHROME_DBUS_EXPORT FileDescriptor {
  35  public:
  36   // Permits initialization without a value for passing to
  37   // dbus::MessageReader::PopFileDescriptor to fill in and from int values.
  38   FileDescriptor() : value_(-1), owner_(false), valid_(false) {}
  39   explicit FileDescriptor(int value) : value_(value), owner_(false),
  40       valid_(false) {}
  41
  42   virtual ~FileDescriptor();
  43
  44   // Retrieves value as an int without affecting ownership.
  45   int value() const;
  46
  47   // Retrieves whether or not the descriptor is ok to send/receive.
  48   int is_valid() const { return valid_; }
  49
  50   // Sets the value and assign ownership.
  51   void PutValue(int value) {
  52     value_ = value;
  53     owner_ = true;
  54     valid_ = false;
  55   }
  56
  57   // Takes the value and ownership.
  58   int TakeValue();
  59
  60   // Checks (and records) validity of the file descriptor.
  61   // We disallow directories to avoid potential sandbox escapes.
  62   // Note this call must be made on a thread where file i/o is allowed.
  63   void CheckValidity();
  64
  65  private:
  66   int value_;
  67   bool owner_;
  68   bool valid_;
  69
  70   DISALLOW_COPY_AND_ASSIGN(FileDescriptor);
  71 };
  72
  73 }  // namespace dbus
  74
  75 #endif  // DBUS_FILE_DESCRIPTOR_H_