Re: [PATCH v2] tty: Fix lookahead_buf crash with serdev

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

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On Thu, 18 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>

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

-- 
 i.

> ---
> 
> Notes:
>     v2: Move more stuff into if block.
> 
>  drivers/tty/tty_buffer.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
> index 9fdecc795b6b..5e287dedce01 100644
> --- a/drivers/tty/tty_buffer.c
> +++ b/drivers/tty/tty_buffer.c
> @@ -470,7 +470,6 @@ static void lookahead_bufs(struct tty_port *port, struct tty_buffer *head)
>  
>  	while (head) {
>  		struct tty_buffer *next;
> -		unsigned char *p, *f = NULL;
>  		unsigned int count;
>  
>  		/*
> @@ -489,11 +488,16 @@ static void lookahead_bufs(struct tty_port *port, struct tty_buffer *head)
>  			continue;
>  		}
>  
> -		p = char_buf_ptr(head, head->lookahead);
> -		if (~head->flags & TTYB_NORMAL)
> -			f = flag_buf_ptr(head, head->lookahead);
> +		if (port->client_ops->lookahead_buf) {
> +			unsigned char *p, *f = NULL;
> +
> +			p = char_buf_ptr(head, head->lookahead);
> +			if (~head->flags & TTYB_NORMAL)
> +				f = flag_buf_ptr(head, head->lookahead);
> +
> +			port->client_ops->lookahead_buf(port, p, f, count);
> +		}
>  
> -		port->client_ops->lookahead_buf(port, p, f, count);
>  		head->lookahead += count;
>  	}
>  }
>