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From:   Rasmus Villemoes <linux@rasmusvillemoes.dk>
To:     Pavel Machek <pavel@ucw.cz>,
        =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?= 
        <u.kleine-koenig@pengutronix.de>,
        Jacek Anaszewski <jacek.anaszewski@gmail.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        linux-leds@vger.kernel.org
Subject: [PATCH v2 1/6] leds: netdev trigger: use memcpy in device_name_store
Date:   Thu, 14 Mar 2019 15:06:14 +0100
Message-Id: <20190314140619.3309-2-linux@rasmusvillemoes.dk>
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References: <20190313202615.22883-1-linux@rasmusvillemoes.dk>
 <20190314140619.3309-1-linux@rasmusvillemoes.dk>
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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@rasmusvillemoes.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;
 
-- 
2.20.1