CVE request: kernel: missing tty ops write function presence check in hci_uart_tty_open()

[Eugene Teo <eugene () redhat com>]

hci_uart_tty_open() is missing check that tty has a write op (a few 
don't), and you should check this at open and refuse if the ops you need 
don't exist, eg as SLIP does:

static int slip_open(struct tty_struct *tty)
{
        struct slip *sl;
        int err;

        if (!capable(CAP_NET_ADMIN))
                return -EPERM;

        if (tty->ops->write == NULL)
                return -EOPNOTSUPP;

https://bugzilla.redhat.com/show_bug.cgi?id=641410
http://git.kernel.org/linus/c19483cc5e56ac5e22dd19cf25ba210ab1537773

Thanks, Eugene