linux-kernel - Re: [PATCH] tty: fix NULL pointer issue when tty

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Date:   Thu, 21 Mar 2019 18:38:47 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Fabien Dessenne <fabien.dessenne@...com>
Cc:     Jiri Slaby <jslaby@...e.com>, linux-kernel@...r.kernel.org,
        Benjamin Gaignard <benjamin.gaignard@...com>
Subject: Re: [PATCH] tty: fix NULL pointer issue when tty_port ops is not set

On Thu, Mar 21, 2019 at 04:43:26PM +0100, Fabien Dessenne wrote:
> Unlike 'client_ops' which is initialized to 'default_client_ops', the
> port operations 'ops' may be left to NULL.
> Check the 'ops' value before checking the 'ops->x' value.
> 
> Signed-off-by: Fabien Dessenne <fabien.dessenne@...com>
> ---
>  drivers/tty/tty_port.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c
> index 044c3cb..a9e12b3 100644
> --- a/drivers/tty/tty_port.c
> +++ b/drivers/tty/tty_port.c
> @@ -325,7 +325,7 @@ static void tty_port_shutdown(struct tty_port *port, struct tty_struct *tty)
>  		if (tty && C_HUPCL(tty))
>  			tty_port_lower_dtr_rts(port);
>  
> -		if (port->ops->shutdown)
> +		if (port->ops && port->ops->shutdown)
>  			port->ops->shutdown(port);
>  	}
>  out:
> @@ -398,7 +398,7 @@ EXPORT_SYMBOL_GPL(tty_port_tty_wakeup);
>   */
>  int tty_port_carrier_raised(struct tty_port *port)
>  {
> -	if (port->ops->carrier_raised == NULL)
> +	if (!port->ops || !port->ops->carrier_raised)
>  		return 1;
>  	return port->ops->carrier_raised(port);
>  }
> @@ -414,7 +414,7 @@ EXPORT_SYMBOL(tty_port_carrier_raised);
>   */
>  void tty_port_raise_dtr_rts(struct tty_port *port)
>  {
> -	if (port->ops->dtr_rts)
> +	if (port->ops && port->ops->dtr_rts)
>  		port->ops->dtr_rts(port, 1);
>  }
>  EXPORT_SYMBOL(tty_port_raise_dtr_rts);
> @@ -429,7 +429,7 @@ EXPORT_SYMBOL(tty_port_raise_dtr_rts);
>   */
>  void tty_port_lower_dtr_rts(struct tty_port *port)
>  {
> -	if (port->ops->dtr_rts)
> +	if (port->ops && port->ops->dtr_rts)
>  		port->ops->dtr_rts(port, 0);
>  }
>  EXPORT_SYMBOL(tty_port_lower_dtr_rts);
> @@ -684,7 +684,7 @@ int tty_port_open(struct tty_port *port, struct tty_struct *tty,
>  
>  	if (!tty_port_initialized(port)) {
>  		clear_bit(TTY_IO_ERROR, &tty->flags);
> -		if (port->ops->activate) {
> +		if (port->ops && port->ops->activate) {
>  			int retval = port->ops->activate(port, tty);
>  			if (retval) {
>  				mutex_unlock(&port->mutex);
> -- 
> 2.7.4
> 

Can you hit this today with any in-kernel drivers?  Or is this only for
your new code you are adding?

thanks,

greg k-h