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SubjectRe: [PATCH] Bluetooth: hci_uart: Switch pty driver to slave side in tty_set_termios()
On Wed, Jan 30, 2019 at 09:13:53PM -0800, Myungho Jung wrote:
> 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@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.

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

That was the other fix. For this one you need to bail out if the tty is
a pty master so that tty_set_termios never gets called here or in
set_baudrate(). Possibly you can do that already at open().

This is also being discussed here:

https://lkml.kernel.org/r/20190130103227.GR3691@localhost

Johan

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