Re: [PATCH] tty: Fix lookahead_buf crash with serdev

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

On Tue, 16 Aug 2022, Vincent Whitchurch wrote:

> Do not follow a NULL pointer if the tty_port_client_operations does not
> implement the ->lookahead_buf() callback, which is the case with
> serdev's ttyport.
> 
> Fixes: 6bb6fa6908ebd3 ("tty: Implement lookahead to process XON/XOFF timely")
> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
> ---
>  drivers/tty/tty_buffer.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
> index 9fdecc795b6b..a1c97d4a45fb 100644
> --- a/drivers/tty/tty_buffer.c
> +++ b/drivers/tty/tty_buffer.c
> @@ -493,7 +493,8 @@ static void lookahead_bufs(struct tty_port *port, struct tty_buffer *head)
>  		if (~head->flags & TTYB_NORMAL)
>  			f = flag_buf_ptr(head, head->lookahead);
>  
> -		port->client_ops->lookahead_buf(port, p, f, count);
> +		if (port->client_ops->lookahead_buf)
> +			port->client_ops->lookahead_buf(port, p, f, count);

While this works, I'd put the preceeding calculations of p and f into the 
same block as they just prep parameters for the call.

>  		head->lookahead += count;
>  	}
>  }
> 

-- 
 i.