ipc/ipc_channel

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This source file includes following definitions.
GetInstance
Lookup
Remove
Insert
SocketWriteErrorIsRecoverable
NotifyProcessForkedForTesting
must_unlink_
SocketPair
CreatePipe
Connect
CloseFileDescriptors
ProcessOutgoingMessages
Send
GetClientFileDescriptor
TakeClientFileDescriptor
CloseClientFileDescriptor
AcceptsConnections
HasAcceptedConnection
GetPeerEuid
ResetToAcceptingConnectionState
IsNamedServerInitialized
SetGlobalPid
OnFileCanReadWithoutBlocking
OnFileCanWriteWithoutBlocking
AcceptConnection
ClosePipeOnError
GetHelloMessageProcId
QueueHelloMessage
ReadData
ReadFileDescriptorsFromFDPipe
WillDispatchInputMessage
DidEmptyInputBuffers
ExtractFileDescriptorsFromMsghdr
ClearInputFDs
QueueCloseFDMessage
HandleInternalMessage
Close
Connect
Close
peer_pid
Send
GetClientFileDescriptor
TakeClientFileDescriptor
AcceptsConnections
HasAcceptedConnection
GetPeerEuid
ResetToAcceptingConnectionState
IsNamedServerInitialized
GenerateVerifiedChannelID
SetGlobalPid
// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "ipc/ipc_channel_posix.h"

#include <errno.h>
#include <fcntl.h>
#include <stddef.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/un.h>
#include <unistd.h>

#if defined(OS_OPENBSD)
#include <sys/uio.h>
#endif

#include <map>
#include <string>

#include "base/command_line.h"
#include "base/file_util.h"
#include "base/files/file_path.h"
#include "base/location.h"
#include "base/logging.h"
#include "base/memory/scoped_ptr.h"
#include "base/memory/singleton.h"
#include "base/posix/eintr_wrapper.h"
#include "base/posix/global_descriptors.h"
#include "base/process/process_handle.h"
#include "base/rand_util.h"
#include "base/stl_util.h"
#include "base/strings/string_util.h"
#include "base/synchronization/lock.h"
#include "ipc/file_descriptor_set_posix.h"
#include "ipc/ipc_descriptors.h"
#include "ipc/ipc_listener.h"
#include "ipc/ipc_logging.h"
#include "ipc/ipc_message_utils.h"
#include "ipc/ipc_switches.h"
#include "ipc/unix_domain_socket_util.h"

namespace IPC {

// IPC channels on Windows use named pipes (CreateNamedPipe()) with
// channel ids as the pipe names.  Channels on POSIX use sockets as
// pipes  These don't quite line up.
//
// When creating a child subprocess we use a socket pair and the parent side of
// the fork arranges it such that the initial control channel ends up on the
// magic file descriptor kPrimaryIPCChannel in the child.  Future
// connections (file descriptors) can then be passed via that
// connection via sendmsg().
//
// A POSIX IPC channel can also be set up as a server for a bound UNIX domain
// socket, and will handle multiple connect and disconnect sequences.  Currently
// it is limited to one connection at a time.

//------------------------------------------------------------------------------
namespace {

// The PipeMap class works around this quirk related to unit tests:
//
// When running as a server, we install the client socket in a
// specific file descriptor number (@kPrimaryIPCChannel). However, we
// also have to support the case where we are running unittests in the
// same process.  (We do not support forking without execing.)
//
// Case 1: normal running
//   The IPC server object will install a mapping in PipeMap from the
//   name which it was given to the client pipe. When forking the client, the
//   GetClientFileDescriptorMapping will ensure that the socket is installed in
//   the magic slot (@kPrimaryIPCChannel). The client will search for the
//   mapping, but it won't find any since we are in a new process. Thus the
//   magic fd number is returned. Once the client connects, the server will
//   close its copy of the client socket and remove the mapping.
//
// Case 2: unittests - client and server in the same process
//   The IPC server will install a mapping as before. The client will search
//   for a mapping and find out. It duplicates the file descriptor and
//   connects. Once the client connects, the server will close the original
//   copy of the client socket and remove the mapping. Thus, when the client
//   object closes, it will close the only remaining copy of the client socket
//   in the fd table and the server will see EOF on its side.
//
// TODO(port): a client process cannot connect to multiple IPC channels with
// this scheme.

class PipeMap {
 public:
  static PipeMap* GetInstance() {
    return Singleton<PipeMap>::get();
  }

  ~PipeMap() {
    // Shouldn't have left over pipes.
    DCHECK(map_.empty());
  }

  // Lookup a given channel id. Return -1 if not found.
  int Lookup(const std::string& channel_id) {
    base::AutoLock locked(lock_);

    ChannelToFDMap::const_iterator i = map_.find(channel_id);
    if (i == map_.end())
      return -1;
    return i->second;
  }

  // Remove the mapping for the given channel id. No error is signaled if the
  // channel_id doesn't exist
  void Remove(const std::string& channel_id) {
    base::AutoLock locked(lock_);
    map_.erase(channel_id);
  }

  // Insert a mapping from @channel_id to @fd. It's a fatal error to insert a
  // mapping if one already exists for the given channel_id
  void Insert(const std::string& channel_id, int fd) {
    base::AutoLock locked(lock_);
    DCHECK_NE(-1, fd);

    ChannelToFDMap::const_iterator i = map_.find(channel_id);
    CHECK(i == map_.end()) << "Creating second IPC server (fd " << fd << ") "
                           << "for '" << channel_id << "' while first "
                           << "(fd " << i->second << ") still exists";
    map_[channel_id] = fd;
  }

 private:
  base::Lock lock_;
  typedef std::map<std::string, int> ChannelToFDMap;
  ChannelToFDMap map_;

  friend struct DefaultSingletonTraits<PipeMap>;
#if defined(OS_ANDROID)
  friend void ::IPC::Channel::NotifyProcessForkedForTesting();
#endif
};

//------------------------------------------------------------------------------

bool SocketWriteErrorIsRecoverable() {
#if defined(OS_MACOSX)
  // On OS X if sendmsg() is trying to send fds between processes and there
  // isn't enough room in the output buffer to send the fd structure over
  // atomically then EMSGSIZE is returned.
  //
  // EMSGSIZE presents a problem since the system APIs can only call us when
  // there's room in the socket buffer and not when there is "enough" room.
  //
  // The current behavior is to return to the event loop when EMSGSIZE is
  // received and hopefull service another FD.  This is however still
  // technically a busy wait since the event loop will call us right back until
  // the receiver has read enough data to allow passing the FD over atomically.
  return errno == EAGAIN || errno == EMSGSIZE;
#else
  return errno == EAGAIN;
#endif  // OS_MACOSX
}

}  // namespace

#if defined(OS_ANDROID)
// When we fork for simple tests on Android, we can't 'exec', so we need to
// reset these entries manually to get the expected testing behavior.
void Channel::NotifyProcessForkedForTesting() {
  PipeMap::GetInstance()->map_.clear();
}
#endif

//------------------------------------------------------------------------------

#if defined(OS_LINUX)
int Channel::ChannelImpl::global_pid_ = 0;
#endif  // OS_LINUX

Channel::ChannelImpl::ChannelImpl(const IPC::ChannelHandle& channel_handle,
                                  Mode mode, Listener* listener)
    : ChannelReader(listener),
      mode_(mode),
      peer_pid_(base::kNullProcessId),
      is_blocked_on_write_(false),
      waiting_connect_(true),
      message_send_bytes_written_(0),
      server_listen_pipe_(-1),
      pipe_(-1),
      client_pipe_(-1),
#if defined(IPC_USES_READWRITE)
      fd_pipe_(-1),
      remote_fd_pipe_(-1),
#endif  // IPC_USES_READWRITE
      pipe_name_(channel_handle.name),
      must_unlink_(false) {
  memset(input_cmsg_buf_, 0, sizeof(input_cmsg_buf_));
  if (!CreatePipe(channel_handle)) {
    // The pipe may have been closed already.
    const char *modestr = (mode_ & MODE_SERVER_FLAG) ? "server" : "client";
    LOG(WARNING) << "Unable to create pipe named \"" << channel_handle.name
                 << "\" in " << modestr << " mode";
  }
}

Channel::ChannelImpl::~ChannelImpl() {
  Close();
}

bool SocketPair(int* fd1, int* fd2) {
  int pipe_fds[2];
  if (socketpair(AF_UNIX, SOCK_STREAM, 0, pipe_fds) != 0) {
    PLOG(ERROR) << "socketpair()";
    return false;
  }

  // Set both ends to be non-blocking.
  if (fcntl(pipe_fds[0], F_SETFL, O_NONBLOCK) == -1 ||
      fcntl(pipe_fds[1], F_SETFL, O_NONBLOCK) == -1) {
    PLOG(ERROR) << "fcntl(O_NONBLOCK)";
    if (IGNORE_EINTR(close(pipe_fds[0])) < 0)
      PLOG(ERROR) << "close";
    if (IGNORE_EINTR(close(pipe_fds[1])) < 0)
      PLOG(ERROR) << "close";
    return false;
  }

  *fd1 = pipe_fds[0];
  *fd2 = pipe_fds[1];

  return true;
}

bool Channel::ChannelImpl::CreatePipe(
    const IPC::ChannelHandle& channel_handle) {
  DCHECK(server_listen_pipe_ == -1 && pipe_ == -1);

  // Four possible cases:
  // 1) It's a channel wrapping a pipe that is given to us.
  // 2) It's for a named channel, so we create it.
  // 3) It's for a client that we implement ourself. This is used
  //    in single-process unittesting.
  // 4) It's the initial IPC channel:
  //   4a) Client side: Pull the pipe out of the GlobalDescriptors set.
  //   4b) Server side: create the pipe.

  int local_pipe = -1;
  if (channel_handle.socket.fd != -1) {
    // Case 1 from comment above.
    local_pipe = channel_handle.socket.fd;
#if defined(IPC_USES_READWRITE)
    // Test the socket passed into us to make sure it is nonblocking.
    // We don't want to call read/write on a blocking socket.
    int value = fcntl(local_pipe, F_GETFL);
    if (value == -1) {
      PLOG(ERROR) << "fcntl(F_GETFL) " << pipe_name_;
      return false;
    }
    if (!(value & O_NONBLOCK)) {
      LOG(ERROR) << "Socket " << pipe_name_ << " must be O_NONBLOCK";
      return false;
    }
#endif   // IPC_USES_READWRITE
  } else if (mode_ & MODE_NAMED_FLAG) {
    // Case 2 from comment above.
    if (mode_ & MODE_SERVER_FLAG) {
      if (!CreateServerUnixDomainSocket(base::FilePath(pipe_name_),
                                        &local_pipe)) {
        return false;
      }
      must_unlink_ = true;
    } else if (mode_ & MODE_CLIENT_FLAG) {
      if (!CreateClientUnixDomainSocket(base::FilePath(pipe_name_),
                                        &local_pipe)) {
        return false;
      }
    } else {
      LOG(ERROR) << "Bad mode: " << mode_;
      return false;
    }
  } else {
    local_pipe = PipeMap::GetInstance()->Lookup(pipe_name_);
    if (mode_ & MODE_CLIENT_FLAG) {
      if (local_pipe != -1) {
        // Case 3 from comment above.
        // We only allow one connection.
        local_pipe = HANDLE_EINTR(dup(local_pipe));
        PipeMap::GetInstance()->Remove(pipe_name_);
      } else {
        // Case 4a from comment above.
        // Guard against inappropriate reuse of the initial IPC channel.  If
        // an IPC channel closes and someone attempts to reuse it by name, the
        // initial channel must not be recycled here.  http://crbug.com/26754.
        static bool used_initial_channel = false;
        if (used_initial_channel) {
          LOG(FATAL) << "Denying attempt to reuse initial IPC channel for "
                     << pipe_name_;
          return false;
        }
        used_initial_channel = true;

        local_pipe =
            base::GlobalDescriptors::GetInstance()->Get(kPrimaryIPCChannel);
      }
    } else if (mode_ & MODE_SERVER_FLAG) {
      // Case 4b from comment above.
      if (local_pipe != -1) {
        LOG(ERROR) << "Server already exists for " << pipe_name_;
        return false;
      }
      base::AutoLock lock(client_pipe_lock_);
      if (!SocketPair(&local_pipe, &client_pipe_))
        return false;
      PipeMap::GetInstance()->Insert(pipe_name_, client_pipe_);
    } else {
      LOG(ERROR) << "Bad mode: " << mode_;
      return false;
    }
  }

#if defined(IPC_USES_READWRITE)
  // Create a dedicated socketpair() for exchanging file descriptors.
  // See comments for IPC_USES_READWRITE for details.
  if (mode_ & MODE_CLIENT_FLAG) {
    if (!SocketPair(&fd_pipe_, &remote_fd_pipe_)) {
      return false;
    }
  }
#endif  // IPC_USES_READWRITE

  if ((mode_ & MODE_SERVER_FLAG) && (mode_ & MODE_NAMED_FLAG)) {
    server_listen_pipe_ = local_pipe;
    local_pipe = -1;
  }

  pipe_ = local_pipe;
  return true;
}

bool Channel::ChannelImpl::Connect() {
  if (server_listen_pipe_ == -1 && pipe_ == -1) {
    DLOG(WARNING) << "Channel creation failed: " << pipe_name_;
    return false;
  }

  bool did_connect = true;
  if (server_listen_pipe_ != -1) {
    // Watch the pipe for connections, and turn any connections into
    // active sockets.
    base::MessageLoopForIO::current()->WatchFileDescriptor(
        server_listen_pipe_,
        true,
        base::MessageLoopForIO::WATCH_READ,
        &server_listen_connection_watcher_,
        this);
  } else {
    did_connect = AcceptConnection();
  }
  return did_connect;
}

void Channel::ChannelImpl::CloseFileDescriptors(Message* msg) {
#if defined(OS_MACOSX)
  // There is a bug on OSX which makes it dangerous to close
  // a file descriptor while it is in transit. So instead we
  // store the file descriptor in a set and send a message to
  // the recipient, which is queued AFTER the message that
  // sent the FD. The recipient will reply to the message,
  // letting us know that it is now safe to close the file
  // descriptor. For more information, see:
  // http://crbug.com/298276
  std::vector<int> to_close;
  msg->file_descriptor_set()->ReleaseFDsToClose(&to_close);
  for (size_t i = 0; i < to_close.size(); i++) {
    fds_to_close_.insert(to_close[i]);
    QueueCloseFDMessage(to_close[i], 2);
  }
#else
  msg->file_descriptor_set()->CommitAll();
#endif
}

bool Channel::ChannelImpl::ProcessOutgoingMessages() {
  DCHECK(!waiting_connect_);  // Why are we trying to send messages if there's
                              // no connection?
  if (output_queue_.empty())
    return true;

  if (pipe_ == -1)
    return false;

  // Write out all the messages we can till the write blocks or there are no
  // more outgoing messages.
  while (!output_queue_.empty()) {
    Message* msg = output_queue_.front();

    size_t amt_to_write = msg->size() - message_send_bytes_written_;
    DCHECK_NE(0U, amt_to_write);
    const char* out_bytes = reinterpret_cast<const char*>(msg->data()) +
        message_send_bytes_written_;

    struct msghdr msgh = {0};
    struct iovec iov = {const_cast<char*>(out_bytes), amt_to_write};
    msgh.msg_iov = &iov;
    msgh.msg_iovlen = 1;
    char buf[CMSG_SPACE(
        sizeof(int) * FileDescriptorSet::kMaxDescriptorsPerMessage)];

    ssize_t bytes_written = 1;
    int fd_written = -1;

    if (message_send_bytes_written_ == 0 &&
        !msg->file_descriptor_set()->empty()) {
      // This is the first chunk of a message which has descriptors to send
      struct cmsghdr *cmsg;
      const unsigned num_fds = msg->file_descriptor_set()->size();

      DCHECK(num_fds <= FileDescriptorSet::kMaxDescriptorsPerMessage);
      if (msg->file_descriptor_set()->ContainsDirectoryDescriptor()) {
        LOG(FATAL) << "Panic: attempting to transport directory descriptor over"
                      " IPC. Aborting to maintain sandbox isolation.";
        // If you have hit this then something tried to send a file descriptor
        // to a directory over an IPC channel. Since IPC channels span
        // sandboxes this is very bad: the receiving process can use openat
        // with ".." elements in the path in order to reach the real
        // filesystem.
      }

      msgh.msg_control = buf;
      msgh.msg_controllen = CMSG_SPACE(sizeof(int) * num_fds);
      cmsg = CMSG_FIRSTHDR(&msgh);
      cmsg->cmsg_level = SOL_SOCKET;
      cmsg->cmsg_type = SCM_RIGHTS;
      cmsg->cmsg_len = CMSG_LEN(sizeof(int) * num_fds);
      msg->file_descriptor_set()->GetDescriptors(
          reinterpret_cast<int*>(CMSG_DATA(cmsg)));
      msgh.msg_controllen = cmsg->cmsg_len;

      // DCHECK_LE above already checks that
      // num_fds < kMaxDescriptorsPerMessage so no danger of overflow.
      msg->header()->num_fds = static_cast<uint16>(num_fds);

#if defined(IPC_USES_READWRITE)
      if (!IsHelloMessage(*msg)) {
        // Only the Hello message sends the file descriptor with the message.
        // Subsequently, we can send file descriptors on the dedicated
        // fd_pipe_ which makes Seccomp sandbox operation more efficient.
        struct iovec fd_pipe_iov = { const_cast<char *>(""), 1 };
        msgh.msg_iov = &fd_pipe_iov;
        fd_written = fd_pipe_;
        bytes_written = HANDLE_EINTR(sendmsg(fd_pipe_, &msgh, MSG_DONTWAIT));
        msgh.msg_iov = &iov;
        msgh.msg_controllen = 0;
        if (bytes_written > 0) {
          CloseFileDescriptors(msg);
        }
      }
#endif  // IPC_USES_READWRITE
    }

    if (bytes_written == 1) {
      fd_written = pipe_;
#if defined(IPC_USES_READWRITE)
      if ((mode_ & MODE_CLIENT_FLAG) && IsHelloMessage(*msg)) {
        DCHECK_EQ(msg->file_descriptor_set()->size(), 1U);
      }
      if (!msgh.msg_controllen) {
        bytes_written = HANDLE_EINTR(write(pipe_, out_bytes, amt_to_write));
      } else
#endif  // IPC_USES_READWRITE
      {
        bytes_written = HANDLE_EINTR(sendmsg(pipe_, &msgh, MSG_DONTWAIT));
      }
    }
    if (bytes_written > 0)
      CloseFileDescriptors(msg);

    if (bytes_written < 0 && !SocketWriteErrorIsRecoverable()) {
      // We can't close the pipe here, because calling OnChannelError
      // may destroy this object, and that would be bad if we are
      // called from Send(). Instead, we return false and hope the
      // caller will close the pipe. If they do not, the pipe will
      // still be closed next time OnFileCanReadWithoutBlocking is
      // called.
#if defined(OS_MACOSX)
      // On OSX writing to a pipe with no listener returns EPERM.
      if (errno == EPERM) {
        return false;
      }
#endif  // OS_MACOSX
      if (errno == EPIPE) {
        return false;
      }
      PLOG(ERROR) << "pipe error on "
                  << fd_written
                  << " Currently writing message of size: "
                  << msg->size();
      return false;
    }

    if (static_cast<size_t>(bytes_written) != amt_to_write) {
      if (bytes_written > 0) {
        // If write() fails with EAGAIN then bytes_written will be -1.
        message_send_bytes_written_ += bytes_written;
      }

      // Tell libevent to call us back once things are unblocked.
      is_blocked_on_write_ = true;
      base::MessageLoopForIO::current()->WatchFileDescriptor(
          pipe_,
          false,  // One shot
          base::MessageLoopForIO::WATCH_WRITE,
          &write_watcher_,
          this);
      return true;
    } else {
      message_send_bytes_written_ = 0;

      // Message sent OK!
      DVLOG(2) << "sent message @" << msg << " on channel @" << this
               << " with type " << msg->type() << " on fd " << pipe_;
      delete output_queue_.front();
      output_queue_.pop();
    }
  }
  return true;
}

bool Channel::ChannelImpl::Send(Message* message) {
  DVLOG(2) << "sending message @" << message << " on channel @" << this
           << " with type " << message->type()
           << " (" << output_queue_.size() << " in queue)";

#ifdef IPC_MESSAGE_LOG_ENABLED
  Logging::GetInstance()->OnSendMessage(message, "");
#endif  // IPC_MESSAGE_LOG_ENABLED

  message->TraceMessageBegin();
  output_queue_.push(message);
  if (!is_blocked_on_write_ && !waiting_connect_) {
    return ProcessOutgoingMessages();
  }

  return true;
}

int Channel::ChannelImpl::GetClientFileDescriptor() {
  base::AutoLock lock(client_pipe_lock_);
  return client_pipe_;
}

int Channel::ChannelImpl::TakeClientFileDescriptor() {
  base::AutoLock lock(client_pipe_lock_);
  int fd = client_pipe_;
  if (client_pipe_ != -1) {
    PipeMap::GetInstance()->Remove(pipe_name_);
    client_pipe_ = -1;
  }
  return fd;
}

void Channel::ChannelImpl::CloseClientFileDescriptor() {
  base::AutoLock lock(client_pipe_lock_);
  if (client_pipe_ != -1) {
    PipeMap::GetInstance()->Remove(pipe_name_);
    if (IGNORE_EINTR(close(client_pipe_)) < 0)
      PLOG(ERROR) << "close " << pipe_name_;
    client_pipe_ = -1;
  }
}

bool Channel::ChannelImpl::AcceptsConnections() const {
  return server_listen_pipe_ != -1;
}

bool Channel::ChannelImpl::HasAcceptedConnection() const {
  return AcceptsConnections() && pipe_ != -1;
}

bool Channel::ChannelImpl::GetPeerEuid(uid_t* peer_euid) const {
  DCHECK(!(mode_ & MODE_SERVER) || HasAcceptedConnection());
  return IPC::GetPeerEuid(pipe_, peer_euid);
}

void Channel::ChannelImpl::ResetToAcceptingConnectionState() {
  // Unregister libevent for the unix domain socket and close it.
  read_watcher_.StopWatchingFileDescriptor();
  write_watcher_.StopWatchingFileDescriptor();
  if (pipe_ != -1) {
    if (IGNORE_EINTR(close(pipe_)) < 0)
      PLOG(ERROR) << "close pipe_ " << pipe_name_;
    pipe_ = -1;
  }
#if defined(IPC_USES_READWRITE)
  if (fd_pipe_ != -1) {
    if (IGNORE_EINTR(close(fd_pipe_)) < 0)
      PLOG(ERROR) << "close fd_pipe_ " << pipe_name_;
    fd_pipe_ = -1;
  }
  if (remote_fd_pipe_ != -1) {
    if (IGNORE_EINTR(close(remote_fd_pipe_)) < 0)
      PLOG(ERROR) << "close remote_fd_pipe_ " << pipe_name_;
    remote_fd_pipe_ = -1;
  }
#endif  // IPC_USES_READWRITE

  while (!output_queue_.empty()) {
    Message* m = output_queue_.front();
    output_queue_.pop();
    delete m;
  }

  // Close any outstanding, received file descriptors.
  ClearInputFDs();

#if defined(OS_MACOSX)
  // Clear any outstanding, sent file descriptors.
  for (std::set<int>::iterator i = fds_to_close_.begin();
       i != fds_to_close_.end();
       ++i) {
    if (IGNORE_EINTR(close(*i)) < 0)
      PLOG(ERROR) << "close";
  }
  fds_to_close_.clear();
#endif
}

// static
bool Channel::ChannelImpl::IsNamedServerInitialized(
    const std::string& channel_id) {
  return base::PathExists(base::FilePath(channel_id));
}

#if defined(OS_LINUX)
// static
void Channel::ChannelImpl::SetGlobalPid(int pid) {
  global_pid_ = pid;
}
#endif  // OS_LINUX

// Called by libevent when we can read from the pipe without blocking.
void Channel::ChannelImpl::OnFileCanReadWithoutBlocking(int fd) {
  if (fd == server_listen_pipe_) {
    int new_pipe = 0;
    if (!ServerAcceptConnection(server_listen_pipe_, &new_pipe) ||
        new_pipe < 0) {
      Close();
      listener()->OnChannelListenError();
    }

    if (pipe_ != -1) {
      // We already have a connection. We only handle one at a time.
      // close our new descriptor.
      if (HANDLE_EINTR(shutdown(new_pipe, SHUT_RDWR)) < 0)
        DPLOG(ERROR) << "shutdown " << pipe_name_;
      if (IGNORE_EINTR(close(new_pipe)) < 0)
        DPLOG(ERROR) << "close " << pipe_name_;
      listener()->OnChannelDenied();
      return;
    }
    pipe_ = new_pipe;

    if ((mode_ & MODE_OPEN_ACCESS_FLAG) == 0) {
      // Verify that the IPC channel peer is running as the same user.
      uid_t client_euid;
      if (!GetPeerEuid(&client_euid)) {
        DLOG(ERROR) << "Unable to query client euid";
        ResetToAcceptingConnectionState();
        return;
      }
      if (client_euid != geteuid()) {
        DLOG(WARNING) << "Client euid is not authorised";
        ResetToAcceptingConnectionState();
        return;
      }
    }

    if (!AcceptConnection()) {
      NOTREACHED() << "AcceptConnection should not fail on server";
    }
    waiting_connect_ = false;
  } else if (fd == pipe_) {
    if (waiting_connect_ && (mode_ & MODE_SERVER_FLAG)) {
      waiting_connect_ = false;
    }
    if (!ProcessIncomingMessages()) {
      // ClosePipeOnError may delete this object, so we mustn't call
      // ProcessOutgoingMessages.
      ClosePipeOnError();
      return;
    }
  } else {
    NOTREACHED() << "Unknown pipe " << fd;
  }

  // If we're a server and handshaking, then we want to make sure that we
  // only send our handshake message after we've processed the client's.
  // This gives us a chance to kill the client if the incoming handshake
  // is invalid. This also flushes any closefd messages.
  if (!is_blocked_on_write_) {
    if (!ProcessOutgoingMessages()) {
      ClosePipeOnError();
    }
  }
}

// Called by libevent when we can write to the pipe without blocking.
void Channel::ChannelImpl::OnFileCanWriteWithoutBlocking(int fd) {
  DCHECK_EQ(pipe_, fd);
  is_blocked_on_write_ = false;
  if (!ProcessOutgoingMessages()) {
    ClosePipeOnError();
  }
}

bool Channel::ChannelImpl::AcceptConnection() {
  base::MessageLoopForIO::current()->WatchFileDescriptor(
      pipe_, true, base::MessageLoopForIO::WATCH_READ, &read_watcher_, this);
  QueueHelloMessage();

  if (mode_ & MODE_CLIENT_FLAG) {
    // If we are a client we want to send a hello message out immediately.
    // In server mode we will send a hello message when we receive one from a
    // client.
    waiting_connect_ = false;
    return ProcessOutgoingMessages();
  } else if (mode_ & MODE_SERVER_FLAG) {
    waiting_connect_ = true;
    return true;
  } else {
    NOTREACHED();
    return false;
  }
}

void Channel::ChannelImpl::ClosePipeOnError() {
  if (HasAcceptedConnection()) {
    ResetToAcceptingConnectionState();
    listener()->OnChannelError();
  } else {
    Close();
    if (AcceptsConnections()) {
      listener()->OnChannelListenError();
    } else {
      listener()->OnChannelError();
    }
  }
}

int Channel::ChannelImpl::GetHelloMessageProcId() {
  int pid = base::GetCurrentProcId();
#if defined(OS_LINUX)
  // Our process may be in a sandbox with a separate PID namespace.
  if (global_pid_) {
    pid = global_pid_;
  }
#endif
  return pid;
}

void Channel::ChannelImpl::QueueHelloMessage() {
  // Create the Hello message
  scoped_ptr<Message> msg(new Message(MSG_ROUTING_NONE,
                                      HELLO_MESSAGE_TYPE,
                                      IPC::Message::PRIORITY_NORMAL));
  if (!msg->WriteInt(GetHelloMessageProcId())) {
    NOTREACHED() << "Unable to pickle hello message proc id";
  }
#if defined(IPC_USES_READWRITE)
  scoped_ptr<Message> hello;
  if (remote_fd_pipe_ != -1) {
    if (!msg->WriteFileDescriptor(base::FileDescriptor(remote_fd_pipe_,
                                                       false))) {
      NOTREACHED() << "Unable to pickle hello message file descriptors";
    }
    DCHECK_EQ(msg->file_descriptor_set()->size(), 1U);
  }
#endif  // IPC_USES_READWRITE
  output_queue_.push(msg.release());
}

Channel::ChannelImpl::ReadState Channel::ChannelImpl::ReadData(
    char* buffer,
    int buffer_len,
    int* bytes_read) {
  if (pipe_ == -1)
    return READ_FAILED;

  struct msghdr msg = {0};

  struct iovec iov = {buffer, static_cast<size_t>(buffer_len)};
  msg.msg_iov = &iov;
  msg.msg_iovlen = 1;

  msg.msg_control = input_cmsg_buf_;

  // recvmsg() returns 0 if the connection has closed or EAGAIN if no data
  // is waiting on the pipe.
#if defined(IPC_USES_READWRITE)
  if (fd_pipe_ >= 0) {
    *bytes_read = HANDLE_EINTR(read(pipe_, buffer, buffer_len));
    msg.msg_controllen = 0;
  } else
#endif  // IPC_USES_READWRITE
  {
    msg.msg_controllen = sizeof(input_cmsg_buf_);
    *bytes_read = HANDLE_EINTR(recvmsg(pipe_, &msg, MSG_DONTWAIT));
  }
  if (*bytes_read < 0) {
    if (errno == EAGAIN) {
      return READ_PENDING;
#if defined(OS_MACOSX)
    } else if (errno == EPERM) {
      // On OSX, reading from a pipe with no listener returns EPERM
      // treat this as a special case to prevent spurious error messages
      // to the console.
      return READ_FAILED;
#endif  // OS_MACOSX
    } else if (errno == ECONNRESET || errno == EPIPE) {
      return READ_FAILED;
    } else {
      PLOG(ERROR) << "pipe error (" << pipe_ << ")";
      return READ_FAILED;
    }
  } else if (*bytes_read == 0) {
    // The pipe has closed...
    return READ_FAILED;
  }
  DCHECK(*bytes_read);

  CloseClientFileDescriptor();

  // Read any file descriptors from the message.
  if (!ExtractFileDescriptorsFromMsghdr(&msg))
    return READ_FAILED;
  return READ_SUCCEEDED;
}

#if defined(IPC_USES_READWRITE)
bool Channel::ChannelImpl::ReadFileDescriptorsFromFDPipe() {
  char dummy;
  struct iovec fd_pipe_iov = { &dummy, 1 };

  struct msghdr msg = { 0 };
  msg.msg_iov = &fd_pipe_iov;
  msg.msg_iovlen = 1;
  msg.msg_control = input_cmsg_buf_;
  msg.msg_controllen = sizeof(input_cmsg_buf_);
  ssize_t bytes_received = HANDLE_EINTR(recvmsg(fd_pipe_, &msg, MSG_DONTWAIT));

  if (bytes_received != 1)
    return true;  // No message waiting.

  if (!ExtractFileDescriptorsFromMsghdr(&msg))
    return false;
  return true;
}
#endif

// On Posix, we need to fix up the file descriptors before the input message
// is dispatched.
//
// This will read from the input_fds_ (READWRITE mode only) and read more
// handles from the FD pipe if necessary.
bool Channel::ChannelImpl::WillDispatchInputMessage(Message* msg) {
  uint16 header_fds = msg->header()->num_fds;
  if (!header_fds)
    return true;  // Nothing to do.

  // The message has file descriptors.
  const char* error = NULL;
  if (header_fds > input_fds_.size()) {
    // The message has been completely received, but we didn't get
    // enough file descriptors.
#if defined(IPC_USES_READWRITE)
    if (!ReadFileDescriptorsFromFDPipe())
      return false;
    if (header_fds > input_fds_.size())
#endif  // IPC_USES_READWRITE
      error = "Message needs unreceived descriptors";
  }

  if (header_fds > FileDescriptorSet::kMaxDescriptorsPerMessage)
    error = "Message requires an excessive number of descriptors";

  if (error) {
    LOG(WARNING) << error
                 << " channel:" << this
                 << " message-type:" << msg->type()
                 << " header()->num_fds:" << header_fds;
    // Abort the connection.
    ClearInputFDs();
    return false;
  }

  // The shenaniganery below with &foo.front() requires input_fds_ to have
  // contiguous underlying storage (such as a simple array or a std::vector).
  // This is why the header warns not to make input_fds_ a deque<>.
  msg->file_descriptor_set()->SetDescriptors(&input_fds_.front(),
                                             header_fds);
  input_fds_.erase(input_fds_.begin(), input_fds_.begin() + header_fds);
  return true;
}

bool Channel::ChannelImpl::DidEmptyInputBuffers() {
  // When the input data buffer is empty, the fds should be too. If this is
  // not the case, we probably have a rogue renderer which is trying to fill
  // our descriptor table.
  return input_fds_.empty();
}

bool Channel::ChannelImpl::ExtractFileDescriptorsFromMsghdr(msghdr* msg) {
  // Check that there are any control messages. On OSX, CMSG_FIRSTHDR will
  // return an invalid non-NULL pointer in the case that controllen == 0.
  if (msg->msg_controllen == 0)
    return true;

  for (cmsghdr* cmsg = CMSG_FIRSTHDR(msg);
       cmsg;
       cmsg = CMSG_NXTHDR(msg, cmsg)) {
    if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_RIGHTS) {
      unsigned payload_len = cmsg->cmsg_len - CMSG_LEN(0);
      DCHECK_EQ(0U, payload_len % sizeof(int));
      const int* file_descriptors = reinterpret_cast<int*>(CMSG_DATA(cmsg));
      unsigned num_file_descriptors = payload_len / 4;
      input_fds_.insert(input_fds_.end(),
                        file_descriptors,
                        file_descriptors + num_file_descriptors);

      // Check this after adding the FDs so we don't leak them.
      if (msg->msg_flags & MSG_CTRUNC) {
        ClearInputFDs();
        return false;
      }

      return true;
    }
  }

  // No file descriptors found, but that's OK.
  return true;
}

void Channel::ChannelImpl::ClearInputFDs() {
  for (size_t i = 0; i < input_fds_.size(); ++i) {
    if (IGNORE_EINTR(close(input_fds_[i])) < 0)
      PLOG(ERROR) << "close ";
  }
  input_fds_.clear();
}

void Channel::ChannelImpl::QueueCloseFDMessage(int fd, int hops) {
  switch (hops) {
    case 1:
    case 2: {
      // Create the message
      scoped_ptr<Message> msg(new Message(MSG_ROUTING_NONE,
                                          CLOSE_FD_MESSAGE_TYPE,
                                          IPC::Message::PRIORITY_NORMAL));
      if (!msg->WriteInt(hops - 1) || !msg->WriteInt(fd)) {
        NOTREACHED() << "Unable to pickle close fd.";
      }
      // Send(msg.release());
      output_queue_.push(msg.release());
      break;
    }

    default:
      NOTREACHED();
      break;
  }
}

void Channel::ChannelImpl::HandleInternalMessage(const Message& msg) {
  // The Hello message contains only the process id.
  PickleIterator iter(msg);

  switch (msg.type()) {
    default:
      NOTREACHED();
      break;

    case Channel::HELLO_MESSAGE_TYPE:
      int pid;
      if (!msg.ReadInt(&iter, &pid))
        NOTREACHED();

#if defined(IPC_USES_READWRITE)
      if (mode_ & MODE_SERVER_FLAG) {
        // With IPC_USES_READWRITE, the Hello message from the client to the
        // server also contains the fd_pipe_, which  will be used for all
        // subsequent file descriptor passing.
        DCHECK_EQ(msg.file_descriptor_set()->size(), 1U);
        base::FileDescriptor descriptor;
        if (!msg.ReadFileDescriptor(&iter, &descriptor)) {
          NOTREACHED();
        }
        fd_pipe_ = descriptor.fd;
        CHECK(descriptor.auto_close);
      }
#endif  // IPC_USES_READWRITE
      peer_pid_ = pid;
      listener()->OnChannelConnected(pid);
      break;

#if defined(OS_MACOSX)
    case Channel::CLOSE_FD_MESSAGE_TYPE:
      int fd, hops;
      if (!msg.ReadInt(&iter, &hops))
        NOTREACHED();
      if (!msg.ReadInt(&iter, &fd))
        NOTREACHED();
      if (hops == 0) {
        if (fds_to_close_.erase(fd) > 0) {
          if (IGNORE_EINTR(close(fd)) < 0)
            PLOG(ERROR) << "close";
        } else {
          NOTREACHED();
        }
      } else {
        QueueCloseFDMessage(fd, hops);
      }
      break;
#endif
  }
}

void Channel::ChannelImpl::Close() {
  // Close can be called multiple time, so we need to make sure we're
  // idempotent.

  ResetToAcceptingConnectionState();

  if (must_unlink_) {
    unlink(pipe_name_.c_str());
    must_unlink_ = false;
  }
  if (server_listen_pipe_ != -1) {
    if (IGNORE_EINTR(close(server_listen_pipe_)) < 0)
      DPLOG(ERROR) << "close " << server_listen_pipe_;
    server_listen_pipe_ = -1;
    // Unregister libevent for the listening socket and close it.
    server_listen_connection_watcher_.StopWatchingFileDescriptor();
  }

  CloseClientFileDescriptor();
}

//------------------------------------------------------------------------------
// Channel's methods simply call through to ChannelImpl.
Channel::Channel(const IPC::ChannelHandle& channel_handle, Mode mode,
                 Listener* listener)
    : channel_impl_(new ChannelImpl(channel_handle, mode, listener)) {
}

Channel::~Channel() {
  delete channel_impl_;
}

bool Channel::Connect() {
  return channel_impl_->Connect();
}

void Channel::Close() {
  if (channel_impl_)
    channel_impl_->Close();
}

base::ProcessId Channel::peer_pid() const {
  return channel_impl_->peer_pid();
}

bool Channel::Send(Message* message) {
  return channel_impl_->Send(message);
}

int Channel::GetClientFileDescriptor() const {
  return channel_impl_->GetClientFileDescriptor();
}

int Channel::TakeClientFileDescriptor() {
  return channel_impl_->TakeClientFileDescriptor();
}

bool Channel::AcceptsConnections() const {
  return channel_impl_->AcceptsConnections();
}

bool Channel::HasAcceptedConnection() const {
  return channel_impl_->HasAcceptedConnection();
}

bool Channel::GetPeerEuid(uid_t* peer_euid) const {
  return channel_impl_->GetPeerEuid(peer_euid);
}

void Channel::ResetToAcceptingConnectionState() {
  channel_impl_->ResetToAcceptingConnectionState();
}

// static
bool Channel::IsNamedServerInitialized(const std::string& channel_id) {
  return ChannelImpl::IsNamedServerInitialized(channel_id);
}

// static
std::string Channel::GenerateVerifiedChannelID(const std::string& prefix) {
  // A random name is sufficient validation on posix systems, so we don't need
  // an additional shared secret.

  std::string id = prefix;
  if (!id.empty())
    id.append(".");

  return id.append(GenerateUniqueRandomChannelID());
}


#if defined(OS_LINUX)
// static
void Channel::SetGlobalPid(int pid) {
  ChannelImpl::SetGlobalPid(pid);
}
#endif  // OS_LINUX

}  // namespace IPC
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root/ipc/ipc_channel_posix.cc

DEFINITIONS
