Re: [PATCH v4] bluetooth: Fix WARNING in tty_set_termios()

[shuah]

On 2/3/19 10:39 PM, Marcel Holtmann wrote:
> Hi Shuah,
>
> > tty_set_termios() has the following WARN_ON which can be triggered with a
> > syscall to invoke TIOCSETD __NR_ioctl.
> >
> > WARN_ON(tty->driver->type == TTY_DRIVER_TYPE_PTY &&
> >                 tty->driver->subtype == PTY_TYPE_MASTER);
> > Reference: https://syzkaller.appspot.com/bug?id=2410d22f1d8e5984217329dd0884b01d99e3e48d
> >
> > "The problem started with commit 7721383f4199 ("Bluetooth: hci_uart: Support
> > operational speed during setup") which introduced a new way for how
> > tty_set_termios() could end up being called for a master pty."
> >
> > Fix it by by preventing setting the HCI line discipline for PTYs in
> > hci_uart_tty_open().
> >
> > Reported-by: syzbot+a950165cbb86bdd023a4@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Cc: Johan Hovold <johan@xxxxxxxxxx>
> > Cc: Marcel Holtmann <marcel@xxxxxxxxxxxx>
> > Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Shuah Khan <shuah@xxxxxxxxxx>
> > ---
> > drivers/bluetooth/hci_ldisc.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
> > index fbf7b4df23ab..c8faa4759cb7 100644
> > --- a/drivers/bluetooth/hci_ldisc.c
> > +++ b/drivers/bluetooth/hci_ldisc.c
> > @@ -475,9 +475,9 @@ static int hci_uart_tty_open(struct tty_struct *tty)
> > 	BT_DBG("tty %p", tty);
> >
> > 	/* Error if the tty has no write op instead of leaving an exploitable
> > -	 * hole
> > +	 * hole. In addition check if setting HCI line discipline is allowed.
> > 	 */
>
> this comment is wrong. The result of setting the HCI line discipline is a call into hci_uart_tty_open. You have to check ops->write and ops->set_termios since both are required. That is it.

I will fix the comment.

> > -	if (tty->ops->write == NULL)
> > +	if (tty->ops->write == NULL || tty->ops->set_termios == NULL)
> > 		return -EOPNOTSUPP;
>
> And while at it, change this to (!tty->ops->write).

Okay. I will fix both.

thanks,
-- Shuah