linux-kernel - Re: [PATCH 10/11] staging: greybus: change strncpy() to strscpy()

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Date: Thu, 28 Mar 2024 23:28:43 +0000
From: Justin Stitt <justinstitt@...gle.com>
To: Arnd Bergmann <arnd@...nel.org>
Cc: linux-kernel@...r.kernel.org, Viresh Kumar <vireshk@...nel.org>, 
	Johan Hovold <johan@...nel.org>, Alex Elder <elder@...nel.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Arnd Bergmann <arnd@...db.de>, 
	Christophe JAILLET <christophe.jaillet@...adoo.fr>, greybus-dev@...ts.linaro.org, linux-staging@...ts.linux.dev
Subject: Re: [PATCH 10/11] staging: greybus: change strncpy() to strscpy()

Hi,

On Thu, Mar 28, 2024 at 03:04:54PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> gcc-10 warns about a strncpy() that does not enforce zero-termination:
> 
> In file included from include/linux/string.h:369,
>                  from drivers/staging/greybus/fw-management.c:9:
> In function 'strncpy',
>     inlined from 'fw_mgmt_backend_fw_update_operation' at drivers/staging/greybus/fw-management.c:306:2:
> include/linux/fortify-string.h:108:30: error: '__builtin_strncpy' specified bound 10 equals destination size [-Werror=stringop-truncation]
>   108 | #define __underlying_strncpy __builtin_strncpy
>       |                              ^
> include/linux/fortify-string.h:187:9: note: in expansion of macro '__underlying_strncpy'
>   187 |  return __underlying_strncpy(p, q, size);
>       |         ^~~~~~~~~~~~~~~~~~~~
> 
> For some reason, I cannot reproduce this with gcc-9 or gcc-11, so I'm not
> sure what's going on. Changing it to strspy() avoids the warning. In this
> case the existing check for zero-termination would fail but can be replaced
> with an error check.
>
>
Arnd, I see 4 instances of strncpy() in this file. Could you clean them
all up at once which would help GREATLY towards:
https://github.com/KSPP/linux/issues/90

strncpy() is an often misued and misunderstood (and deprecated [1])
string API, let's get rid of that thing all together!

[1]: https://www.kernel.org/doc/html/latest/process/deprecated.html#strcpy

> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> This is from randconfig testing with random gcc versions, a .config to
> reproduce is at https://pastebin.com/r13yezkU
> ---
>  drivers/staging/greybus/fw-management.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/greybus/fw-management.c b/drivers/staging/greybus/fw-management.c
> index 3054f084d777..35bfdd5f32d2 100644
> --- a/drivers/staging/greybus/fw-management.c
> +++ b/drivers/staging/greybus/fw-management.c
> @@ -303,13 +303,13 @@ static int fw_mgmt_backend_fw_update_operation(struct fw_mgmt *fw_mgmt,
>  	struct gb_fw_mgmt_backend_fw_update_request request;
>  	int ret;
>  
> -	strncpy(request.firmware_tag, tag, GB_FIRMWARE_TAG_MAX_SIZE);
> +	ret = strscpy(request.firmware_tag, tag, GB_FIRMWARE_TAG_MAX_SIZE);
>  
>  	/*
>  	 * The firmware-tag should be NULL terminated, otherwise throw error and
>  	 * fail.
>  	 */
> -	if (request.firmware_tag[GB_FIRMWARE_TAG_MAX_SIZE - 1] != '\0') {
> +	if (ret == -E2BIG) {
>  		dev_err(fw_mgmt->parent, "backend-update: firmware-tag is not NULL terminated\n");
>  		return -EINVAL;
>  	}
> -- 
> 2.39.2
> 
Thanks
Justin