net: mdio_bus: replace deprecated strncpy with strscpy

strncpy() is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

We expect mdiodev->modalias to be NUL-terminated based on its usage with
strcmp():
|       return strcmp(mdiodev->modalias, drv->name) == 0;

Moreover, mdiodev->modalias is already zero-allocated:
|       mdiodev = kzalloc(sizeof(*mdiodev), GFP_KERNEL);
... which means the NUL-padding strncpy provides is not necessary.

Considering the above, a suitable replacement is `strscpy` [2] due to
the fact that it guarantees NUL-termination on the destination buffer
without unnecessarily NUL-padding.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c
index 25dcaa4..6cf73c1 100644 (file)
--- a/drivers/net/phy/mdio_bus.c
+++ b/drivers/net/phy/mdio_bus.c
@@ -506,7 +506,7 @@ static int mdiobus_create_device(struct mii_bus *bus,
        if (IS_ERR(mdiodev))
                return -ENODEV;
 
-       strncpy(mdiodev->modalias, bi->modalias,
+       strscpy(mdiodev->modalias, bi->modalias,
                sizeof(mdiodev->modalias));
        mdiodev->bus_match = mdio_device_bus_match;
        mdiodev->dev.platform_data = (void *)bi->platform_data;