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

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Date:	Tue, 08 Mar 2016 13:01:09 -0800
From:	Joe Perches <joe@...ches.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

On Tue, 2016-03-08 at 21:40 +0100, 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.
[]
> diff --git 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);
> +		dev_dbg(&instance->usb_intf->dev, "%.3d : %*ph", i, j, data + i);
> +		i += j;
>  	}
>  	return i;
>  }

Maybe use print_dump_hex_debug()