vm_tools/vsh/vsh_client.cc

// Copyright 2017 The Chromium OS 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 "vm_tools/vsh/vsh_client.h"

#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <string.h>
#include <termios.h>
#include <unistd.h>

#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/types.h>

#include <linux/vm_sockets.h>  // Needs to come after sys/socket.h

#include <memory>
#include <string>
#include <utility>
#include <vector>

#include <base/at_exit.h>
#include <base/bind.h>
#include <base/bind_helpers.h>
#include <base/files/file_util.h>
#include <base/files/scoped_file.h>
#include <base/location.h>
#include <base/message_loop/message_loop.h>
#include <base/posix/eintr_wrapper.h>
#include <base/strings/string_split.h>
#include <brillo/asynchronous_signal_handler.h>
#include <brillo/flag_helper.h>
#include <brillo/message_loops/base_message_loop.h>
#include <brillo/syslog_logging.h>

#include "vm_tools/common/constants.h"
#include "vm_tools/vsh/scoped_termios.h"
#include "vm_tools/vsh/utils.h"
#include "vsh.pb.h"  // NOLINT(build/include)

using std::string;

namespace vm_tools {
namespace vsh {

// Pick a default exit status that will make it obvious if the remote end
// exited abnormally.
constexpr int kDefaultExitCode = 123;

std::unique_ptr<VshClient> VshClient::Create(base::ScopedFD sock_fd,
                                             const std::string& user,
                                             const std::string& container) {
  auto client = std::unique_ptr<VshClient>(new VshClient(std::move(sock_fd)));

  if (!client->Init(user, container)) {
    return nullptr;
  }

  return client;
}

VshClient::VshClient(base::ScopedFD sock_fd)
    : sock_fd_(std::move(sock_fd)),
      stdin_task_(brillo::MessageLoop::kTaskIdNull),
      exit_code_(kDefaultExitCode) {}

bool VshClient::Init(const std::string& user, const std::string& container) {
  // Set up the connection with the guest. The setup process is:
  //
  // 1) Client opens connection and sends a SetupConnectionRequest.
  // 2) Server responds with a SetupConnectionResponse. If the response
  //    does not indicate READY status, the client must exit immediately.
  // 3) If the client receives READY, the server and client may exchange
  //    HostMessage and GuestMessage protobufs, with GuestMessages flowing
  //    from client(host) to server(guest), and vice versa for HostMessages.
  // 4) If the client or server receives a message with a new ConnectionStatus
  //    that does not indicate READY, the recepient must exit.
  // TODO(smbarber): Connect to an lxd container instead of the VM.
  SetupConnectionRequest connection_request;
  if (container.empty()) {
    connection_request.set_target(vm_tools::vsh::kVmShell);
  } else {
    connection_request.set_target(container);
  }

  connection_request.set_user(user);

  auto env = connection_request.mutable_env();

  // Default to forwarding the current TERM variable.
  const char* term_env = getenv("TERM");
  if (term_env)
    (*env)["TERM"] = std::string(term_env);

  base::CommandLine* cl = base::CommandLine::ForCurrentProcess();
  std::vector<std::string> args = cl->GetArgs();

  // Forward any environment variables/args passed on the command line.
  bool env_done = false;
  for (const auto& arg : args) {
    if (!env_done) {
      std::vector<std::string> components = base::SplitString(
          arg, "=", base::TRIM_WHITESPACE, base::SPLIT_WANT_NONEMPTY);

      if (components.size() != 2) {
        env_done = true;
        connection_request.add_argv(arg);
      } else {
        (*env)[std::move(components[0])] = std::move(components[1]);
      }
    } else {
      connection_request.add_argv(arg);
    }
  }

  struct winsize ws;
  if (!GetCurrentWindowSize(&ws)) {
    LOG(ERROR) << "Failed to get initial window size";
    return false;
  }

  connection_request.set_window_rows(ws.ws_row);
  connection_request.set_window_cols(ws.ws_col);

  if (!SendMessage(sock_fd_.get(), connection_request)) {
    LOG(ERROR) << "Failed to send connection request";
    return false;
  }

  SetupConnectionResponse connection_response;
  if (!RecvMessage(sock_fd_.get(), &connection_response)) {
    LOG(ERROR) << "Failed to receive response from vshd";
    return false;
  }

  ConnectionStatus status = connection_response.status();
  if (status != READY) {
    LOG(ERROR) << "Server was unable to set up connection: "
               << connection_response.description();
    return false;
  }

  brillo::MessageLoop* message_loop = brillo::MessageLoop::current();
  message_loop->WatchFileDescriptor(
      FROM_HERE, sock_fd_.get(), brillo::MessageLoop::WatchMode::kWatchRead,
      true,
      base::Bind(&VshClient::HandleVsockReadable, base::Unretained(this)));
  stdin_task_ = message_loop->WatchFileDescriptor(
      FROM_HERE, STDIN_FILENO, brillo::MessageLoop::WatchMode::kWatchRead, true,
      base::Bind(&VshClient::HandleStdinReadable, base::Unretained(this)));

  // Handle termination signals and SIGWINCH.
  signal_handler_.Init();
  for (int signal : {SIGINT, SIGTERM, SIGHUP, SIGQUIT}) {
    signal_handler_.RegisterHandler(
        signal,
        base::Bind(&VshClient::HandleTermSignal, base::Unretained(this)));
  }
  signal_handler_.RegisterHandler(
      SIGWINCH,
      base::Bind(&VshClient::HandleWindowResizeSignal, base::Unretained(this)));

  return true;
}

// Handles a signal that is expected to terminate the process by exiting
// the main message loop.
bool VshClient::HandleTermSignal(const struct signalfd_siginfo& siginfo) {
  Shutdown();
  return true;
}

// Handles a window resize signal by sending the current window size to the
// remote.
bool VshClient::HandleWindowResizeSignal(
    const struct signalfd_siginfo& siginfo) {
  DCHECK_EQ(siginfo.ssi_signo, SIGWINCH);

  SendCurrentWindowSize();

  // This return value indicates whether or not the signal handler should be
  // unregistered! So, even if this succeeds, this should return false.
  return false;
}

// Receives a host message from the guest and takes action.
void VshClient::HandleVsockReadable() {
  HostMessage host_message;
  if (!RecvMessage(sock_fd_.get(), &host_message)) {
    PLOG(ERROR) << "Failed to receive message from server";
    Shutdown();
    return;
  }

  switch (host_message.msg_case()) {
    case HostMessage::kDataMessage: {
      // Data messages from the guest should go to stdout.
      DataMessage data_message = host_message.data_message();
      DCHECK_EQ(data_message.stream(), STDOUT_STREAM);

      if (!base::WriteFileDescriptor(STDOUT_FILENO, data_message.data().data(),
                                     data_message.data().size())) {
        PLOG(ERROR) << "Failed to write data to stdout";
        return;
      }
      break;
    }
    case HostMessage::kStatusMessage: {
      // The remote side has an updated connection status, which likely means
      // it's time to Shutdown().
      ConnectionStatusMessage status_message = host_message.status_message();
      ConnectionStatus status = status_message.status();

      if (status == EXITED) {
        exit_code_ = status_message.code();
        Shutdown();
      } else if (status != READY) {
        LOG(ERROR) << "vsh connection has exited abnormally: " << status;
        Shutdown();
        return;
      }
      break;
    }
    default:
      LOG(ERROR) << "Received unknown host message of type: "
                 << host_message.msg_case();
  }
}

// Forwards input from the host to the remote pseudoterminal.
void VshClient::HandleStdinReadable() {
  uint8_t buf[kMaxDataSize];
  GuestMessage guest_message;
  DataMessage* data_message = guest_message.mutable_data_message();

  ssize_t count = HANDLE_EINTR(read(STDIN_FILENO, buf, sizeof(buf)));

  if (count < 0) {
    PLOG(ERROR) << "Failed to read from stdin";
    Shutdown();
    return;
  } else if (count == 0) {
    brillo::MessageLoop* message_loop = brillo::MessageLoop::current();
    message_loop->CancelTask(stdin_task_);
    stdin_task_ = brillo::MessageLoop::kTaskIdNull;
  }

  data_message->set_stream(STDIN_STREAM);
  data_message->set_data(buf, count);

  if (!SendMessage(sock_fd_.get(), guest_message)) {
    LOG(ERROR) << "Failed to send guest data message";
    // Sending a partial message will break framing. Shut down the connection.
    Shutdown();
    return;
  }
}

bool VshClient::SendCurrentWindowSize() {
  GuestMessage guest_message;
  WindowResizeMessage* resize_message = guest_message.mutable_resize_message();

  struct winsize ws;
  if (!GetCurrentWindowSize(&ws)) {
    return false;
  }

  resize_message->set_rows(ws.ws_row);
  resize_message->set_cols(ws.ws_col);

  if (!SendMessage(sock_fd_.get(), guest_message)) {
    LOG(ERROR) << "Failed to send tty window resize message";
    Shutdown();
    return false;
  }

  return true;
}

bool VshClient::GetCurrentWindowSize(struct winsize* ws) {
  DCHECK(ws);
  if (!isatty(STDIN_FILENO)) {
    ws->ws_row = 0;
    ws->ws_col = 0;
    return true;
  }

  if (ioctl(STDIN_FILENO, TIOCGWINSZ, ws) < 0) {
    PLOG(ERROR) << "Failed to get tty window size";
    return false;
  }

  return true;
}

int VshClient::exit_code() {
  return exit_code_;
}

}  // namespace vsh
}  // namespace vm_tools