linux-kernel - Re: [PATCH 1/4] leds: netdev trigger: use memcpy in device_name

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Message-ID: <20190314100416.5ywtxhsbhqz6rvdq@pengutronix.de>
Date:   Thu, 14 Mar 2019 11:04:16 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Pavel Machek <pavel@....cz>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        LKML <linux-kernel@...r.kernel.org>, linux-leds@...r.kernel.org
Subject: Re: [PATCH 1/4] leds: netdev trigger: use memcpy in device_name_store

On Thu, Mar 14, 2019 at 10:57:14AM +0100, Rasmus Villemoes wrote:
> On 14/03/2019 10.29, Uwe Kleine-König wrote:
> > Hello,
> > 
> > On Wed, Mar 13, 2019 at 09:26:12PM +0100, Rasmus Villemoes wrote:
> >> --- a/drivers/leds/trigger/ledtrig-netdev.c
> >> +++ b/drivers/leds/trigger/ledtrig-netdev.c
> >> @@ -122,7 +122,8 @@ static ssize_t device_name_store(struct device *dev,
> >>  		trigger_data->net_dev = NULL;
> >>  	}
> >>  
> >> -	strncpy(trigger_data->device_name, buf, size);
> >> +	memcpy(trigger_data->device_name, buf, size);
> >> +	trigger_data->device_name[size] = '\0';
> > 
> > This is open-coding
> > 
> > 	strlcpy(trigger_data->device_name, buf, size);
> 
> No. size here is the number of bytes userspace wrote, which never (well,
> almost never, they could do something odd) contain a nul byte. Passing
> that as size to strlcpy would guarantee that we chopped off the last
> character from the user input.

You're right here, strlcpy isn't a replacement here. I withdraw my
suggestion.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |