linux-kernel - Re: [PATCH v2 1/6] leds: netdev trigger: use memcpy in device_name

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Date:   Tue, 26 Mar 2019 20:53:20 +0100
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Pavel Machek <pavel@....cz>,
        Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-leds@...r.kernel.org
Subject: Re: [PATCH v2 1/6] leds: netdev trigger: use memcpy in
 device_name_store

Hi Rasmus,

Thank you for the patch.

On 3/14/19 3:06 PM, Rasmus Villemoes wrote:
> If userspace doesn't end the input with a newline (which can easily
> happen if the write happens from a C program that does write(fd,
> iface, strlen(iface))), we may end up including garbage from a
> previous, longer value in the device_name. For example
> 
> # cat device_name
> 
> # printf 'eth12' > device_name
> # cat device_name
> eth12
> # printf 'eth3' > device_name
> # cat device_name
> eth32
> 
> I highly doubt anybody is relying on this behaviour, so switch to
> simply copying the bytes (we've already checked that size is <
> IFNAMSIZ) and unconditionally zero-terminate it; of course, we also
> still have to strip a trailing newline.
> 
> This is also preparation for future patches.
> 
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
> ---
>   drivers/leds/trigger/ledtrig-netdev.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/leds/trigger/ledtrig-netdev.c b/drivers/leds/trigger/ledtrig-netdev.c
> index 3dd3ed46d473..8d476b92f58c 100644
> --- 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;
>   	if (size > 0 && trigger_data->device_name[size - 1] == '\n')
>   		trigger_data->device_name[size - 1] = 0;
>   
> 

Added tag:

Fixes: 06f502f57d0d ("leds: trigger: Introduce a NETDEV trigger")

and applied to the fixes-for-5.1-rc3 branch.

-- 
Best regards,
Jacek Anaszewski