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      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 IPC_IPC_CHANNEL_POSIX_H_
      6 #define IPC_IPC_CHANNEL_POSIX_H_
      7 
      8 #include "ipc/ipc_channel.h"
      9 
     10 #include <sys/socket.h>  // for CMSG macros
     11 
     12 #include <queue>
     13 #include <set>
     14 #include <string>
     15 #include <vector>
     16 
     17 #include "base/message_loop/message_loop.h"
     18 #include "base/process/process.h"
     19 #include "ipc/file_descriptor_set_posix.h"
     20 #include "ipc/ipc_channel_reader.h"
     21 
     22 #if !defined(OS_MACOSX)
     23 // On Linux, the seccomp sandbox makes it very expensive to call
     24 // recvmsg() and sendmsg(). The restriction on calling read() and write(), which
     25 // are cheap, is that we can't pass file descriptors over them.
     26 //
     27 // As we cannot anticipate when the sender will provide us with file
     28 // descriptors, we have to make the decision about whether we call read() or
     29 // recvmsg() before we actually make the call. The easiest option is to
     30 // create a dedicated socketpair() for exchanging file descriptors. Any file
     31 // descriptors are split out of a message, with the non-file-descriptor payload
     32 // going over the normal connection, and the file descriptors being sent
     33 // separately over the other channel. When read()ing from a channel, we'll
     34 // notice if the message was supposed to have come with file descriptors and
     35 // use recvmsg on the other socketpair to retrieve them and combine them
     36 // back with the rest of the message.
     37 //
     38 // Mac can also run in IPC_USES_READWRITE mode if necessary, but at this time
     39 // doesn't take a performance hit from recvmsg and sendmsg, so it doesn't
     40 // make sense to waste resources on having the separate dedicated socketpair.
     41 // It is however useful for debugging between Linux and Mac to be able to turn
     42 // this switch 'on' on the Mac as well.
     43 //
     44 // The HELLO message from the client to the server is always sent using
     45 // sendmsg because it will contain the file descriptor that the server
     46 // needs to send file descriptors in later messages.
     47 #define IPC_USES_READWRITE 1
     48 #endif
     49 
     50 namespace IPC {
     51 
     52 class Channel::ChannelImpl : public internal::ChannelReader,
     53                              public base::MessageLoopForIO::Watcher {
     54  public:
     55   // Mirror methods of Channel, see ipc_channel.h for description.
     56   ChannelImpl(const IPC::ChannelHandle& channel_handle, Mode mode,
     57               Listener* listener);
     58   virtual ~ChannelImpl();
     59   bool Connect();
     60   void Close();
     61   bool Send(Message* message);
     62   int GetClientFileDescriptor();
     63   int TakeClientFileDescriptor();
     64   void CloseClientFileDescriptor();
     65   bool AcceptsConnections() const;
     66   bool HasAcceptedConnection() const;
     67   bool GetPeerEuid(uid_t* peer_euid) const;
     68   void ResetToAcceptingConnectionState();
     69   base::ProcessId peer_pid() const { return peer_pid_; }
     70   static bool IsNamedServerInitialized(const std::string& channel_id);
     71 #if defined(OS_LINUX)
     72   static void SetGlobalPid(int pid);
     73 #endif  // OS_LINUX
     74 
     75  private:
     76   bool CreatePipe(const IPC::ChannelHandle& channel_handle);
     77 
     78   bool ProcessOutgoingMessages();
     79 
     80   bool AcceptConnection();
     81   void ClosePipeOnError();
     82   int GetHelloMessageProcId();
     83   void QueueHelloMessage();
     84   void CloseFileDescriptors(Message* msg);
     85   void QueueCloseFDMessage(int fd, int hops);
     86 
     87   // ChannelReader implementation.
     88   virtual ReadState ReadData(char* buffer,
     89                              int buffer_len,
     90                              int* bytes_read) OVERRIDE;
     91   virtual bool WillDispatchInputMessage(Message* msg) OVERRIDE;
     92   virtual bool DidEmptyInputBuffers() OVERRIDE;
     93   virtual void HandleInternalMessage(const Message& msg) OVERRIDE;
     94 
     95 #if defined(IPC_USES_READWRITE)
     96   // Reads the next message from the fd_pipe_ and appends them to the
     97   // input_fds_ queue. Returns false if there was a message receiving error.
     98   // True means there was a message and it was processed properly, or there was
     99   // no messages.
    100   bool ReadFileDescriptorsFromFDPipe();
    101 #endif
    102 
    103   // Finds the set of file descriptors in the given message.  On success,
    104   // appends the descriptors to the input_fds_ member and returns true
    105   //
    106   // Returns false if the message was truncated. In this case, any handles that
    107   // were sent will be closed.
    108   bool ExtractFileDescriptorsFromMsghdr(msghdr* msg);
    109 
    110   // Closes all handles in the input_fds_ list and clears the list. This is
    111   // used to clean up handles in error conditions to avoid leaking the handles.
    112   void ClearInputFDs();
    113 
    114   // MessageLoopForIO::Watcher implementation.
    115   virtual void OnFileCanReadWithoutBlocking(int fd) OVERRIDE;
    116   virtual void OnFileCanWriteWithoutBlocking(int fd) OVERRIDE;
    117 
    118   Mode mode_;
    119 
    120   base::ProcessId peer_pid_;
    121 
    122   // After accepting one client connection on our server socket we want to
    123   // stop listening.
    124   base::MessageLoopForIO::FileDescriptorWatcher
    125   server_listen_connection_watcher_;
    126   base::MessageLoopForIO::FileDescriptorWatcher read_watcher_;
    127   base::MessageLoopForIO::FileDescriptorWatcher write_watcher_;
    128 
    129   // Indicates whether we're currently blocked waiting for a write to complete.
    130   bool is_blocked_on_write_;
    131   bool waiting_connect_;
    132 
    133   // If sending a message blocks then we use this variable
    134   // to keep track of where we are.
    135   size_t message_send_bytes_written_;
    136 
    137   // File descriptor we're listening on for new connections if we listen
    138   // for connections.
    139   int server_listen_pipe_;
    140 
    141   // The pipe used for communication.
    142   int pipe_;
    143 
    144   // For a server, the client end of our socketpair() -- the other end of our
    145   // pipe_ that is passed to the client.
    146   int client_pipe_;
    147   base::Lock client_pipe_lock_;  // Lock that protects |client_pipe_|.
    148 
    149 #if defined(IPC_USES_READWRITE)
    150   // Linux/BSD use a dedicated socketpair() for passing file descriptors.
    151   int fd_pipe_;
    152   int remote_fd_pipe_;
    153 #endif
    154 
    155   // The "name" of our pipe.  On Windows this is the global identifier for
    156   // the pipe.  On POSIX it's used as a key in a local map of file descriptors.
    157   std::string pipe_name_;
    158 
    159   // Messages to be sent are queued here.
    160   std::queue<Message*> output_queue_;
    161 
    162   // We assume a worst case: kReadBufferSize bytes of messages, where each
    163   // message has no payload and a full complement of descriptors.
    164   static const size_t kMaxReadFDs =
    165       (Channel::kReadBufferSize / sizeof(IPC::Message::Header)) *
    166       FileDescriptorSet::kMaxDescriptorsPerMessage;
    167 
    168   // Buffer size for file descriptors used for recvmsg. On Mac the CMSG macros
    169   // don't seem to be constant so we have to pick a "large enough" value.
    170 #if defined(OS_MACOSX)
    171   static const size_t kMaxReadFDBuffer = 1024;
    172 #else
    173   static const size_t kMaxReadFDBuffer = CMSG_SPACE(sizeof(int) * kMaxReadFDs);
    174 #endif
    175 
    176   // Temporary buffer used to receive the file descriptors from recvmsg.
    177   // Code that writes into this should immediately read them out and save
    178   // them to input_fds_, since this buffer will be re-used anytime we call
    179   // recvmsg.
    180   char input_cmsg_buf_[kMaxReadFDBuffer];
    181 
    182   // File descriptors extracted from messages coming off of the channel. The
    183   // handles may span messages and come off different channels from the message
    184   // data (in the case of READWRITE), and are processed in FIFO here.
    185   // NOTE: The implementation assumes underlying storage here is contiguous, so
    186   // don't change to something like std::deque<> without changing the
    187   // implementation!
    188   std::vector<int> input_fds_;
    189 
    190 #if defined(OS_MACOSX)
    191   // On OSX, sent FDs must not be closed until we get an ack.
    192   // Keep track of sent FDs here to make sure the remote is not
    193   // trying to bamboozle us.
    194   std::set<int> fds_to_close_;
    195 #endif
    196 
    197   // True if we are responsible for unlinking the unix domain socket file.
    198   bool must_unlink_;
    199 
    200 #if defined(OS_LINUX)
    201   // If non-zero, overrides the process ID sent in the hello message.
    202   static int global_pid_;
    203 #endif  // OS_LINUX
    204 
    205   DISALLOW_IMPLICIT_CONSTRUCTORS(ChannelImpl);
    206 };
    207 
    208 }  // namespace IPC
    209 
    210 #endif  // IPC_IPC_CHANNEL_POSIX_H_
    211