// setupConsole sets up the console from inside the container, and sends the
// master pty fd to the config.Pipe (using cmsg). This is done to ensure that
// consoles are scoped to a container properly (see runc#814 and the many
// issues related to that). This has to be run *after* we've pivoted to the new
// rootfs (and the users' configuration is entirely set up).
func setupConsole(pipe *os.File, config *initConfig, mount bool) error {
// At this point, /dev/ptmx points to something that we would expect. We
// used to change the owner of the slave path, but since the /dev/pts mount
// can have gid=X set (at the users' option). So touching the owner of the
// slave PTY is not necessary, as the kernel will handle that for us. Note
// however, that setupUser (specifically fixStdioPermissions) *will* change
// the UID owner of the console to be the user the process will run as (so
// they can actually control their console).
console, err := newConsole()
if err != nil {
return err
}
// After we return from here, we don't need the console anymore.
defer console.Close()
linuxConsole, ok := console.(*linuxConsole)
if !ok {
return fmt.Errorf("failed to cast console to *linuxConsole")
}
// Mount the console inside our rootfs.
if mount {
if err := linuxConsole.mount(); err != nil {
return err
}
}
if err := writeSync(pipe, procConsole); err != nil {
return err
}
// We need to have a two-way synchronisation here. Though it might seem
// pointless, it's important to make sure that the sendmsg(2) payload
// doesn't get swallowed by an out-of-place read(2) [which happens if the
// syscalls get reordered so that sendmsg(2) is before the other side's
// read(2) of procConsole].
if err := readSync(pipe, procConsoleReq); err != nil {
return err
}
// While we can access console.master, using the API is a good idea.
if err := utils.SendFd(pipe, linuxConsole.File()); err != nil {
return err
}
// Make sure the other side recieved the fd.
if err := readSync(pipe, procConsoleAck); err != nil {
return err
}
// Now, dup over all the things.
return linuxConsole.dupStdio()
}
func (t *tty) sendtty(socket *os.File, ti *libcontainer.TerminalInfo) error {
if t.console == nil {
return fmt.Errorf("tty.console not set")
}
// Create a fake file to contain the terminal info.
console := os.NewFile(t.console.File().Fd(), ti.String())
if err := utils.SendFd(socket, console); err != nil {
return err
}
return nil
}