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SubjectRe: [PATCH v3] bluetooth: Fix WARNING in tty_set_termios()
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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
>
> Johan Hovold said: "The problemm 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(). Looked into keying off of tty and ldisc ops, and
> couldn't find any that would be conclusive. Checking tty as such clearly
> tags the reason for rejecting the request to set ldisc.
>
> Reported-by: syzbot+a950165cbb86bdd023a4@syzkaller.appspotmail.com
> Cc: Johan Hovold <johan@kernel.org>
> Cc: Marcel Holtmann <marcel@holtmann.org>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Signed-off-by: Shuah Khan <shuah@kernel.org>
> ---
> drivers/bluetooth/hci_ldisc.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
> index fbf7b4df23ab..a3d313fcc0f2 100644
> --- a/drivers/bluetooth/hci_ldisc.c
> +++ b/drivers/bluetooth/hci_ldisc.c
> @@ -480,6 +480,11 @@ static int hci_uart_tty_open(struct tty_struct *tty)
> if (tty->ops->write == NULL)
> return -EOPNOTSUPP;
>
> + /* don't set HCI line discipline on PTYs */
> + if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
> + tty->driver->subtype == PTY_TYPE_MASTER)
> + return -EINVAL;
> +

this is turning in circles. What is wrong with checking !tty->ops->set_termios here?

Regards

Marcel

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