linux-hardening - Re: [PATCH] um: vector: refactor deprecated strncpy

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Message-ID: <0bdda692-25a3-227c-69ef-341f037e1dd7@cambridgegreys.com>
Date:   Tue, 8 Aug 2023 07:04:29 +0100
From:   Anton Ivanov <anton.ivanov@...bridgegreys.com>
To:     Justin Stitt <justinstitt@...gle.com>,
        Richard Weinberger <richard@....at>,
        Johannes Berg <johannes@...solutions.net>
Cc:     linux-um@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Kees Cook <keescook@...omium.org>,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] um: vector: refactor deprecated strncpy


On 07/08/2023 19:22, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> 
> A suitable replacement is `strscpy` [2] due to the fact that it
> guarantees NUL-termination on its destination buffer argument which is
> _not_ the case for `strncpy`!
> 
> In this case, we are able to drop the now superfluous `... - 1`
> instances because `strscpy` will automatically truncate the last byte by
> setting it to a NUL byte if the source size exceeds the destination size
> or if the source string is not NUL-terminated.
> 
> I've also opted to remove the seemingly useless char* casts. I'm not
> sure why they're present at all since (after expanding the `ifr_name`
> macro) `ifr.ifr_ifrn.ifrn_name` is a char* already.
> 
> All in all, `strscpy` is a more robust and less ambiguous interface
> while also letting us remove some `... -1`'s which cleans things up a
> bit.
> 
> [1]: www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
> [2]: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html
> 
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@...r.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>
> ---
>   arch/um/drivers/vector_user.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/um/drivers/vector_user.c b/arch/um/drivers/vector_user.c
> index c650e428432b..c719e1ec4645 100644
> --- a/arch/um/drivers/vector_user.c
> +++ b/arch/um/drivers/vector_user.c
> @@ -141,7 +141,7 @@ static int create_tap_fd(char *iface)
>   	}
>   	memset(&ifr, 0, sizeof(ifr));
>   	ifr.ifr_flags = IFF_TAP | IFF_NO_PI | IFF_VNET_HDR;
> -	strncpy((char *)&ifr.ifr_name, iface, sizeof(ifr.ifr_name) - 1);
> +	strscpy(ifr.ifr_name, iface, sizeof(ifr.ifr_name));
>   
>   	err = ioctl(fd, TUNSETIFF, (void *) &ifr);
>   	if (err != 0) {
> @@ -171,7 +171,7 @@ static int create_raw_fd(char *iface, int flags, int proto)
>   		goto raw_fd_cleanup;
>   	}
>   	memset(&ifr, 0, sizeof(ifr));
> -	strncpy((char *)&ifr.ifr_name, iface, sizeof(ifr.ifr_name) - 1);
> +	strscpy(ifr.ifr_name, iface, sizeof(ifr.ifr_name));
>   	if (ioctl(fd, SIOCGIFINDEX, (void *) &ifr) < 0) {
>   		err = -errno;
>   		goto raw_fd_cleanup;
> 
> ---
> base-commit: c1a515d3c0270628df8ae5f5118ba859b85464a2
> change-id: 20230807-arch-um-drivers-ad44050885d0
> 
> Best regards,
> --
> Justin Stitt <justinstitt@...gle.com>
> 
> 
> _______________________________________________
> linux-um mailing list
> linux-um@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-um
> 
Acked-by: Anton Ivanov <anton.ivanov@...bridgegreys.com>

-- 
Anton R. Ivanov
Cambridgegreys Limited. Registered in England. Company Number 10273661
https://www.cambridgegreys.com/

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