linux-kernel - Re: [RFC 7/7] USB: usbatm: avoid fragile and inefficient snprintf use

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Message-ID: <56E02052.80507@cogentembedded.com>
Date:	Wed, 9 Mar 2016 16:08:34 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Kees Cook <keescook@...omium.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Duncan Sands <duncan.sands@...e.fr>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 7/7] USB: usbatm: avoid fragile and inefficient snprintf use

Hello.

On 3/8/2016 11:40 PM, Rasmus Villemoes wrote:

> Passing overlapping source and destination is fragile, and in this
> case we can even simplify the code and avoid the huge stack buffer by
> using the %p extension for printing a small hex dump.
>
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
> ---
>   drivers/usb/atm/usbatm.c | 11 ++++-------
>   1 file changed, 4 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/usb/atm/usbatm.c b/drivers/usb/atm/usbatm.c
> index db322d9ccb6e..fb47f9883056 100644
> --- a/drivers/usb/atm/usbatm.c
> +++ b/drivers/usb/atm/usbatm.c
> @@ -1331,15 +1331,12 @@ MODULE_VERSION(DRIVER_VERSION);
>   static int usbatm_print_packet(struct usbatm_data *instance,
>   			       const unsigned char *data, int len)
>   {
> -	unsigned char buffer[256];
> -	int i = 0, j = 0;
> +	int i, j;
>
>   	for (i = 0; i < len;) {
> -		buffer[0] = '\0';
> -		sprintf(buffer, "%.3d :", i);
> -		for (j = 0; (j < 16) && (i < len); j++, i++)
> -			sprintf(buffer, "%s %2.2x", buffer, data[i]);
> -		dev_dbg(&instance->usb_intf->dev, "%s", buffer);
> +		j = min(16, len-i);

    Kernel style assumes spaces on either side of the operators, like below, no?

> +		dev_dbg(&instance->usb_intf->dev, "%.3d : %*ph", i, j, data + i);
> +		i += j;
>   	}
>   	return i;
>   }

MBR, Sergei