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SubjectRe: [PATCH] Bluetooth: hci_uart: Switch pty driver to slave side in tty_set_termios()
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@syzkaller.appspotmail.com
> Signed-off-by: Myungho Jung <mhjungk@gmail.com>
> ---
> 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

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