[PATCH 4.19 72/72] leds: trigger: netdev: use memcpy in device_name_store

[Greg Kroah-Hartman]

[ Upstream commit 909346433064b8d840dc82af26161926b8d37558 ]

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.

Fixes: 06f502f57d0d ("leds: trigger: Introduce a NETDEV trigger")
Signed-off-by: Rasmus Villemoes <li...@rasmusvillemoes.dk>
Acked-by: Pavel Machek <pa...@ucw.cz>
Signed-off-by: Jacek Anaszewski <jacek.anaszew...@gmail.com>
Signed-off-by: Sasha Levin (Microsoft) <sas...@kernel.org>
---
 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 167a94c02d05..136f86a1627d 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;
 
-- 
2.19.1