linux-kernel - Re: [PATCH 04/12] usb: gadget: uvc: Replace snprintf() with the safer scnprintf() variant

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Date:   Wed, 13 Dec 2023 18:47:35 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Lee Jones <lee@...nel.org>
Cc:     gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org,
        Daniel Scally <dan.scally@...asonboard.com>,
        Andrzej Pietrasiewicz <andrzejtp2010@...il.com>
Subject: Re: [PATCH 04/12] usb: gadget: uvc: Replace snprintf() with the
 safer scnprintf() variant

Hi Lee,

Thank you for the patch.

On Wed, Dec 13, 2023 at 04:42:33PM +0000, Lee Jones wrote:
> There is a general misunderstanding amongst engineers that {v}snprintf()
> returns the length of the data *actually* encoded into the destination
> array.  However, as per the C99 standard {v}snprintf() really returns
> the length of the data that *would have been* written if there were
> enough space for it.  This misunderstanding has led to buffer-overruns
> in the past.  It's generally considered safer to use the {v}scnprintf()
> variants in their place (or even sprintf() in simple cases).  So let's
> do that.
> 
> Link: https://lwn.net/Articles/69419/
> Link: https://github.com/KSPP/linux/issues/105
> Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> Cc: Daniel Scally <dan.scally@...asonboard.com>
> Cc: Andrzej Pietrasiewicz <andrzejtp2010@...il.com>
> Signed-off-by: Lee Jones <lee@...nel.org>

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

> ---
>  drivers/usb/gadget/function/uvc_configfs.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/gadget/function/uvc_configfs.c b/drivers/usb/gadget/function/uvc_configfs.c
> index 9bf0e985acfab..7e704b2bcfd1c 100644
> --- a/drivers/usb/gadget/function/uvc_configfs.c
> +++ b/drivers/usb/gadget/function/uvc_configfs.c
> @@ -3414,7 +3414,7 @@ static ssize_t f_uvc_opts_string_##cname##_show(struct config_item *item,\
>  	int result;							\
>  									\
>  	mutex_lock(&opts->lock);					\
> -	result = snprintf(page, sizeof(opts->aname), "%s", opts->aname);\
> +	result = scnprintf(page, sizeof(opts->aname), "%s", opts->aname);\
>  	mutex_unlock(&opts->lock);					\
>  									\
>  	return result;							\

-- 
Regards,

Laurent Pinchart