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 mdio_bus_id to be NUL-terminated based on its use with snprint(): | snprintf(priv->phy_name, MII_BUS_ID_SIZE, PHY_ID_FMT, | mdio_bus_id, phy_id); Moreover, as this is the only use of mdio_bus_id, we can see that NUL-padding is not required. 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. Note that for the replacement involving cpmac_mii->id, the source buffer's length is equal to MII_BUS_ID_SIZE which could result in a buffer overread. However, there is no buffer overread since "cpmac-1" (the string copied into cpmac_mii->id) is smaller than MII_BUS_ID_SIZE thus meaning the previous usage of strncpy() here did _not_ have any overread bugs. Nonetheless, let's still favor strscpy() over strncpy(). 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: [email protected] Signed-off-by: Justin Stitt <[email protected]> --- Note: build-tested only. Found with: $ rg "strncpy\(" --- drivers/net/ethernet/ti/cpmac.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/drivers/net/ethernet/ti/cpmac.c b/drivers/net/ethernet/ti/cpmac.c index 80eeeb463c4f..714328ee7487 100644 --- a/drivers/net/ethernet/ti/cpmac.c +++ b/drivers/net/ethernet/ti/cpmac.c @@ -1068,7 +1068,7 @@ static int cpmac_probe(struct platform_device *pdev) pdata = dev_get_platdata(&pdev->dev); if (external_switch || dumb_switch) { - strncpy(mdio_bus_id, "fixed-0", MII_BUS_ID_SIZE); /* fixed phys bus */ + strscpy(mdio_bus_id, "fixed-0", sizeof(mdio_bus_id)); /* fixed phys bus */ phy_id = pdev->id; } else { for (phy_id = 0; phy_id < PHY_MAX_ADDR; phy_id++) { @@ -1076,7 +1076,8 @@ static int cpmac_probe(struct platform_device *pdev) continue; if (!mdiobus_get_phy(cpmac_mii, phy_id)) continue; - strncpy(mdio_bus_id, cpmac_mii->id, MII_BUS_ID_SIZE); + strscpy(mdio_bus_id, cpmac_mii->id, + sizeof(mdio_bus_id)); break; } } @@ -1084,10 +1085,9 @@ static int cpmac_probe(struct platform_device *pdev) if (phy_id == PHY_MAX_ADDR) { dev_err(&pdev->dev, "no PHY present, falling back " "to switch on MDIO bus 0\n"); - strncpy(mdio_bus_id, "fixed-0", MII_BUS_ID_SIZE); /* fixed phys bus */ + strscpy(mdio_bus_id, "fixed-0", sizeof(mdio_bus_id)); /* fixed phys bus */ phy_id = pdev->id; } - mdio_bus_id[sizeof(mdio_bus_id) - 1] = '\0'; dev = alloc_etherdev_mq(sizeof(*priv), CPMAC_QUEUES); if (!dev) --- base-commit: cbf3a2cb156a2c911d8f38d8247814b4c07f49a2 change-id: 20231012-strncpy-drivers-net-ethernet-ti-cpmac-c-9d9d1b33d595 Best regards, -- Justin Stitt <[email protected]>
