Re: [PATCH] Bluetooth: hci_uart: Switch pty driver to slave side in tty_set_termios()

[Myungho Jung]

On Wed, Jan 30, 2019 at 11:07:38AM +0100, Johan Hovold wrote:
> On Sun, Jan 27, 2019 at 10:53:02PM -0800, Myungho Jung wrote:
> > tty_set_termios() should be called with slave side of pty driver. So, If
> > tty driver is pty master, it needs to be switched to ->link.
> 
> I'm not sure that's the right solution. PTYs are virtual devices used
> for IPC and neither end (master or slave) have support for modem
> control or baud rates.
> 
> > Reported-by: syzbot+a950165cbb86bdd023a4@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Signed-off-by: Myungho Jung <mhjungk@xxxxxxxxx>
> > ---
> >  drivers/bluetooth/hci_ldisc.c | 20 +++++++++++++++-----
> >  1 file changed, 15 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
> > index fbf7b4df23ab..90c5ea8c399b 100644
> > --- a/drivers/bluetooth/hci_ldisc.c
> > +++ b/drivers/bluetooth/hci_ldisc.c
> > @@ -299,10 +299,18 @@ static int hci_uart_send_frame(struct hci_dev *hdev, struct sk_buff *skb)
> >  	return 0;
> >  }
> >  
> > +/* If driver is pty master, return slave side */
> > +static struct tty_struct *hci_uart_get_real_tty(struct tty_struct *tty)
> > +{
> > +	return  (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
> > +		 tty->driver->subtype == PTY_TYPE_MASTER) ? tty->link : tty;
> > +}
> > +
> >  /* Flow control or un-flow control the device */
> >  void hci_uart_set_flow_control(struct hci_uart *hu, bool enable)
> >  {
> >  	struct tty_struct *tty = hu->tty;
> > +	struct tty_struct *real_tty;
> >  	struct ktermios ktermios;
> >  	int status;
> >  	unsigned int set = 0;
> > @@ -314,11 +322,12 @@ void hci_uart_set_flow_control(struct hci_uart *hu, bool enable)
> >  		return;
> >  	}
> >  
> > +	real_tty = hci_uart_get_real_tty(tty);
> >  	if (enable) {
> >  		/* Disable hardware flow control */
> > -		ktermios = tty->termios;
> > +		ktermios = real_tty->termios;
> >  		ktermios.c_cflag &= ~CRTSCTS;
> > -		status = tty_set_termios(tty, &ktermios);
> > +		status = tty_set_termios(real_tty, &ktermios);
> >  		BT_DBG("Disabling hardware flow control: %s",
> >  		       status ? "failed" : "success");
> 
> So instead of these pointless calls to set the slave termios and
> modem-control state, you might as well bail out early above (and
> similarly in set_baudrate()).
> 
> Using n_hci for a master pty really makes no sense at all, so we could
> even bail out at ldisc open, but perhaps that can be discussed and
> addressed later.
> 
> Johan

Hi Johan,

I fixed it to just return -EOPNOTSUPP if NULL in ath_setup().

Thanks,
Myungho