tty: release_one_tty() forgets to put pids

release_one_tty(tty) can be called when tty still has a reference
to pgrp/session. In this case we leak the pid.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Catalin Marinas <catalin.marinas@arm.com>
Reported-and-tested-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/char/tty_io.c

@@ -1423,6 +1423,8 @@ static void release_one_tty(struct work_struct *work)
 	list_del_init(&tty->tty_files);
 	file_list_unlock();
 
+	put_pid(tty->pgrp);
+	put_pid(tty->session);
 	free_tty_struct(tty);
 }