NULL dereference in tty_open()

[Dan Carpenter <dan.carpenter@oracle.com>]

There is a NULL dereference here.  It was artificially triggered so
not a huge priority.

drivers/tty/tty_io.c
  1893          retval = tty_add_file(tty, filp);
  1894          if (retval) {
  1895                  tty_unlock();
  1896                  tty_release(inode, filp);
  1897                  return retval;
  1898          }

tty_add_file() is supposed to setup filp->private_data but the
allocation fails.  In tty_release() we call file_tty(filp),
__tty_fasync() and tty_del_file() which dereference
filp->private_data and Oops.

I looked at ptmx_open() to see how the error handling was done there.
That function only calls tty_release() if tty_add_file() succeeds,
so maybe we could just call devpts_kill_index() here and remove the
tty_release()?  I don't know the code well enough to say.

regards,
dan carpenter