Re: [PATCH 3/3] [v2] staging: greybus: change strncpy() to strscpy_pad()

[Justin Stitt]

Hi,

On Mon, Apr 08, 2024 at 09:48:11PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
> 
> 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, and I only
> get a warning for one of the four related strncpy()s, so I'm not
> sure what's going on.
> 
> Change all four to strscpy_pad(), which is the safest replacement here,
> as it avoids ending up with uninitialized stack data in the tag name.
> 
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>

This patch helps out with [1].

Reviewed-by: Justin Stitt <justinstitt@xxxxxxxxxx>

> ---
> v2
>  - use strscpy_pad()
>  - use two-argument form
>  - change all four instances, not just the one that produced the warning
> ---
>  drivers/staging/greybus/fw-management.c | 12 +++++-------
>  1 file changed, 5 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/staging/greybus/fw-management.c b/drivers/staging/greybus/fw-management.c
> index 3054f084d777..a47385175582 100644
> --- a/drivers/staging/greybus/fw-management.c
> +++ b/drivers/staging/greybus/fw-management.c
> @@ -123,8 +123,7 @@ static int fw_mgmt_interface_fw_version_operation(struct fw_mgmt *fw_mgmt,
>  	fw_info->major = le16_to_cpu(response.major);
>  	fw_info->minor = le16_to_cpu(response.minor);
>  
> -	strncpy(fw_info->firmware_tag, response.firmware_tag,
> -		GB_FIRMWARE_TAG_MAX_SIZE);
> +	strscpy_pad(fw_info->firmware_tag, response.firmware_tag);
>  
>  	/*
>  	 * The firmware-tag should be NULL terminated, otherwise throw error but
> @@ -153,7 +152,7 @@ static int fw_mgmt_load_and_validate_operation(struct fw_mgmt *fw_mgmt,
>  	}
>  
>  	request.load_method = load_method;
> -	strncpy(request.firmware_tag, tag, GB_FIRMWARE_TAG_MAX_SIZE);
> +	strscpy_pad(request.firmware_tag, tag);
>  
>  	/*
>  	 * The firmware-tag should be NULL terminated, otherwise throw error and
> @@ -249,8 +248,7 @@ static int fw_mgmt_backend_fw_version_operation(struct fw_mgmt *fw_mgmt,
>  	struct gb_fw_mgmt_backend_fw_version_response response;
>  	int ret;
>  
> -	strncpy(request.firmware_tag, fw_info->firmware_tag,
> -		GB_FIRMWARE_TAG_MAX_SIZE);
> +	strscpy_pad(request.firmware_tag, fw_info->firmware_tag);
>  
>  	/*
>  	 * The firmware-tag should be NULL terminated, otherwise throw error and
> @@ -303,13 +301,13 @@ 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_pad(request.firmware_tag, tag);
>  
>  	/*
>  	 * 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
> 
>

Link: https://github.com/KSPP/linux/issues/90 [1]

Thanks
Justin