linux-kernel - Re: [PATCH 14/22] [media] usbvision-i2c: fix format overflow warning

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Date:   Mon, 17 Jul 2017 14:53:01 +0200
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Guenter Roeck <linux@...ck-us.net>, akpm@...ux-foundation.org,
        netdev@...r.kernel.org, "David S . Miller" <davem@...emloft.net>,
        "James E . J . Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org, x86@...nel.org,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        linux-media@...r.kernel.org
Subject: Re: [PATCH 14/22] [media] usbvision-i2c: fix format overflow warning

On 14/07/17 14:07, Arnd Bergmann wrote:
> gcc-7 notices that we copy a fixed length string into another
> string of the same size, with additional characters:
> 
> drivers/media/usb/usbvision/usbvision-i2c.c: In function 'usbvision_i2c_register':
> drivers/media/usb/usbvision/usbvision-i2c.c:190:36: error: '%d' directive writing between 1 and 11 bytes into a region of size between 0 and 47 [-Werror=format-overflow=]
>   sprintf(usbvision->i2c_adap.name, "%s-%d-%s", i2c_adap_template.name,
>                                     ^~~~~~~~~~
> drivers/media/usb/usbvision/usbvision-i2c.c:190:2: note: 'sprintf' output between 4 and 76 bytes into a destination of size 48
> 
> We know this is fine as the template name is always "usbvision", so
> we can easily avoid the warning by using this as the format string
> directly.

Hmm, how about replacing sprintf by snprintf? That feels a lot safer (this is very
old code, it's not surprising it is still using sprintf).

Regards,

	Hans

> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/media/usb/usbvision/usbvision-i2c.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/usb/usbvision/usbvision-i2c.c b/drivers/media/usb/usbvision/usbvision-i2c.c
> index fdf6b6e285da..aae9f69884da 100644
> --- a/drivers/media/usb/usbvision/usbvision-i2c.c
> +++ b/drivers/media/usb/usbvision/usbvision-i2c.c
> @@ -187,8 +187,8 @@ int usbvision_i2c_register(struct usb_usbvision *usbvision)
>  
>  	usbvision->i2c_adap = i2c_adap_template;
>  
> -	sprintf(usbvision->i2c_adap.name, "%s-%d-%s", i2c_adap_template.name,
> -		usbvision->dev->bus->busnum, usbvision->dev->devpath);
> +	sprintf(usbvision->i2c_adap.name, "usbvision-%d-%s",
> +		 usbvision->dev->bus->busnum, usbvision->dev->devpath);
>  	PDEBUG(DBG_I2C, "Adaptername: %s", usbvision->i2c_adap.name);
>  	usbvision->i2c_adap.dev.parent = &usbvision->dev->dev;
>  
>