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Message-ID: <202310161239.2C067C04@keescook> Date: Mon, 16 Oct 2023 12:40:34 -0700 From: Kees Cook <keescook@...omium.org> To: Justin Stitt <justinstitt@...gle.com> Cc: 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>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH] net: mdio: replace deprecated strncpy with strscpy On Thu, Oct 12, 2023 at 09:43:02PM +0000, Justin Stitt wrote: > 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 new_bus->id to be NUL-terminated but not NUL-padded based on > its prior assignment through snprintf: > | snprintf(new_bus->id, MII_BUS_ID_SIZE, "gpio-%x", bus_id); > > Due to this, 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/mdio/mdio-gpio.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/net/mdio/mdio-gpio.c b/drivers/net/mdio/mdio-gpio.c > index 0fb3c2de0845..a1718d646504 100644 > --- a/drivers/net/mdio/mdio-gpio.c > +++ b/drivers/net/mdio/mdio-gpio.c > @@ -125,7 +125,7 @@ static struct mii_bus *mdio_gpio_bus_init(struct device *dev, > if (bus_id != -1) > snprintf(new_bus->id, MII_BUS_ID_SIZE, "gpio-%x", bus_id); > else > - strncpy(new_bus->id, "gpio", MII_BUS_ID_SIZE); > + strscpy(new_bus->id, "gpio", sizeof(new_bus->id)); struct mii_bus { ... char id[MII_BUS_ID_SIZE]; Yup, looks good. (I wonder about changing to sizeof() in the snprintf() above it, but for a strscpy() refactor, I think this is fine.) Reviewed-by: Kees Cook <keescook@...omium.org> -- Kees Cook
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