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

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

[Myungho Jung]

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.

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");
 
@@ -350,9 +359,9 @@ void hci_uart_set_flow_control(struct hci_uart *hu, bool enable)
 		BT_DBG("Setting RTS: %s", status ? "failed" : "success");
 
 		/* Re-enable 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("Enabling hardware flow control: %s",
 		       status ? "failed" : "success");
 	}
@@ -367,9 +376,10 @@ void hci_uart_set_speeds(struct hci_uart *hu, unsigned int init_speed,
 
 void hci_uart_set_baudrate(struct hci_uart *hu, unsigned int speed)
 {
-	struct tty_struct *tty = hu->tty;
+	struct tty_struct *tty;
 	struct ktermios ktermios;
 
+	tty = hci_uart_get_real_tty(hu->tty);
 	ktermios = tty->termios;
 	ktermios.c_cflag &= ~CBAUD;
 	tty_termios_encode_baud_rate(&ktermios, speed, speed);
-- 
2.17.1

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

[Marcel Holtmann]

Hi Myungho,

> 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.
> 
> 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;
> +}
> +

	if (tty->driver->type == TTY_DRIVER_PTY && tty->driver->subtype = PTY_TYPE_MASTER)
		return tty->link;

	return tty;

We can spare the extra two lines to make this readable.

> /* 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);

I would add a comment above this call why this is done and then also add an empty line after it. The if clause is not related to that call at all.

> 	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");
> 
> @@ -350,9 +359,9 @@ void hci_uart_set_flow_control(struct hci_uart *hu, bool enable)
> 		BT_DBG("Setting RTS: %s", status ? "failed" : "success");
> 
> 		/* Re-enable 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("Enabling hardware flow control: %s",
> 		       status ? "failed" : "success");
> 	}
> @@ -367,9 +376,10 @@ void hci_uart_set_speeds(struct hci_uart *hu, unsigned int init_speed,
> 
> void hci_uart_set_baudrate(struct hci_uart *hu, unsigned int speed)
> {
> -	struct tty_struct *tty = hu->tty;
> +	struct tty_struct *tty;
> 	struct ktermios ktermios;
> 
> +	tty = hci_uart_get_real_tty(hu->tty);

Same here. Add comment above and the also an extra empty line.

> 	ktermios = tty->termios;
> 	ktermios.c_cflag &= ~CBAUD;
> 	tty_termios_encode_baud_rate(&ktermios, speed, speed);

Regards

Marcel

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

[Johan Hovold]

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

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@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

Hi Johan,

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

Thanks,
Myungho

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

[Johan Hovold]

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