linux-hardening - [PATCH] net: mdio: replace deprecated strncpy with strscpy

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Message-ID: <20231012-strncpy-drivers-net-phy-mdio_bus-c-v1-1-15242e6f9ec4@google.com>
Date: Thu, 12 Oct 2023 21:53:03 +0000
From: Justin Stitt <justinstitt@...gle.com>
To: Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>, 
	Russell King <linux@...linux.org.uk>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-hardening@...r.kernel.org, Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] net: mdio: 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 [1]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@...r.kernel.org
Signed-off-by: Justin Stitt <justinstitt@...gle.com>
---
Note: build-tested only.

Found with: $ rg "strncpy\("
---
 drivers/net/phy/mdio_bus.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c
index 25dcaa49ab8b..6cf73c15635b 100644
--- 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;

---
base-commit: cbf3a2cb156a2c911d8f38d8247814b4c07f49a2
change-id: 20231012-strncpy-drivers-net-phy-mdio_bus-c-0a0d5e875712

Best regards,
--
Justin Stitt <justinstitt@...gle.com>