linux-kernel - Re: [PATCH] usb: typec: avoid format-overflow warning

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Date:   Mon, 9 Jul 2018 11:27:32 +0300
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: typec: avoid format-overflow warning

On Fri, Jul 06, 2018 at 03:28:32PM +0200, Arnd Bergmann wrote:
> gcc-8 points out that the fix-byte buffer might be too small if
> desc->mode is a three-digit number:
> 
> drivers/usb/typec/class.c: In function 'typec_register_altmode':
> drivers/usb/typec/class.c:502:32: error: '%d' directive writing between 1 and 3 bytes into a region of size 2 [-Werror=format-overflow=]
>   sprintf(alt->group_name, "mode%d", desc->mode);
>                                 ^~
> drivers/usb/typec/class.c:502:27: note: directive argument in the range [0, 255]
>   sprintf(alt->group_name, "mode%d", desc->mode);
>                            ^~~~~~~~
> drivers/usb/typec/class.c:502:2: note: 'sprintf' output between 6 and 8 bytes into a destination of size 6
>   sprintf(alt->group_name, "mode%d", desc->mode);
>   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> I assume this cannot happen in practice, but we can simply make the
> string long enough to avoid the warning. This uses the two padding
> bytes that already exist after the string.
> 
> Fixes: 4ab8c18d4d67 ("usb: typec: Register a device for every mode")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Acked-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>

> ---
>  drivers/usb/typec/bus.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/typec/bus.h b/drivers/usb/typec/bus.h
> index 62aaf8b56bde..db40e61d8b72 100644
> --- a/drivers/usb/typec/bus.h
> +++ b/drivers/usb/typec/bus.h
> @@ -16,7 +16,7 @@ struct altmode {
>  	enum typec_port_data		roles;
>  
>  	struct attribute		*attrs[5];
> -	char				group_name[6];
> +	char				group_name[8];
>  	struct attribute_group		group;
>  	const struct attribute_group	*groups[2];
>  

Thanks,

-- 
heikki