linux-kernel - Re: [PATCH 1/2] media: cec: extron-da-hd-4k-plus: Fix Wformat-truncation

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Message-ID: <0017bba6-0c46-4c74-9bd1-3b0e3ea9877a@xs4all.nl>
Date: Tue, 1 Apr 2025 09:46:18 +0200
From: Hans Verkuil <hverkuil@...all.nl>
To: Ricardo Ribalda <ribalda@...omium.org>,
 Mauro Carvalho Chehab <mchehab@...nel.org>,
 Hans de Goede <hdegoede@...hat.com>,
 Sakari Ailus <sakari.ailus@...ux.intel.com>,
 Andy Shevchenko <andy@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-staging@...ts.linux.dev
Subject: Re: [PATCH 1/2] media: cec: extron-da-hd-4k-plus: Fix
 Wformat-truncation

On 31/03/2025 18:38, Ricardo Ribalda wrote:
> Convince gcc8 that the port, initiator and destination fits in a single
> char, despite the fact that they are 4 bits wide.
> 
> drivers/media/cec/usb/extron-da-hd-4k-plus/extron-da-hd-4k-plus.c:1014:44: warning: 'DCEC' directive output may be truncated writing 4 bytes into a region of size between 0 and 53 [-Wformat-truncation=]
> 
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> ---
>  drivers/media/cec/usb/extron-da-hd-4k-plus/extron-da-hd-4k-plus.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/cec/usb/extron-da-hd-4k-plus/extron-da-hd-4k-plus.c b/drivers/media/cec/usb/extron-da-hd-4k-plus/extron-da-hd-4k-plus.c
> index cfbfc4c1b2e67fec9434aa6852ab465ad8c11225..e1a2a676bcaf9c313041ce8074c85636cfe4b2da 100644
> --- a/drivers/media/cec/usb/extron-da-hd-4k-plus/extron-da-hd-4k-plus.c
> +++ b/drivers/media/cec/usb/extron-da-hd-4k-plus/extron-da-hd-4k-plus.c
> @@ -1012,8 +1012,9 @@ static int extron_cec_adap_transmit(struct cec_adapter *adap, u8 attempts,
>  	for (i = 0; i < msg->len - 1; i++)
>  		sprintf(buf + i * 3, "%%%02X", msg->msg[i + 1]);
>  	snprintf(cmd, sizeof(cmd), "W%c%u*%u*%u*%sDCEC",
> -		 port->direction, port->port.port,
> -		 cec_msg_initiator(msg), cec_msg_destination(msg), buf);
> +		 port->direction, port->port.port % 10,
> +		 cec_msg_initiator(msg) % 10, cec_msg_destination(msg) % 10,

This is definitely wrong, since initiator/destination is a value from 0-15.
So % 10 will mess that up.

I'm preparing a patch of my own for this.

Regards,

	Hans

> +		 buf);
>  	return extron_send_and_wait(port->extron, port, cmd, NULL);
>  }
>  
>