Re: [PATCH 02/11] scsi: devinfo: rework scsi_strcpy_devinfo()

[Justin Stitt]

Hi,

On Thu, Mar 28, 2024 at 03:04:46PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
> 
> scsi_strcpy_devinfo() appears to work as intended but its semantics are
> so confusing that gcc warns about it when -Wstringop-truncation is enabled:
> 
> In function 'scsi_strcpy_devinfo',
>     inlined from 'scsi_dev_info_list_add_keyed' at drivers/scsi/scsi_devinfo.c:370:2:
> drivers/scsi/scsi_devinfo.c:297:9: error: 'strncpy' specified bound 16 equals destination size [-Werror=stringop-truncation]
>   297 |         strncpy(to, from, to_length);
>       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Reorganize the function to completely separate the nul-terminated from
> the space-padded/non-terminated case. The former is just strscpy_pad(),
> while the latter does not have a standard function.
>

I did the same in a patch sent earlier (few weeks ago):

https://lore.kernel.org/all/20240305-strncpy-drivers-scsi-mpi3mr-mpi3mr_fw-c-v3-5-5b78a13ff984@xxxxxxxxxx/

Maybe reviewers can chime in on which version is preferred and go from
there.

> 
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
>  drivers/scsi/scsi_devinfo.c | 30 ++++++++++++++++++++----------
>  1 file changed, 20 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/scsi/scsi_devinfo.c b/drivers/scsi/scsi_devinfo.c
> index ba7237e83863..58726c15ebac 100644
> --- a/drivers/scsi/scsi_devinfo.c
> +++ b/drivers/scsi/scsi_devinfo.c
> @@ -290,18 +290,28 @@ static struct scsi_dev_info_list_table *scsi_devinfo_lookup_by_key(int key)
>  static void scsi_strcpy_devinfo(char *name, char *to, size_t to_length,
>  				char *from, int compatible)
>  {
> -	size_t from_length;
> +	int ret;
>  
> -	from_length = strlen(from);
> -	/* This zero-pads the destination */
> -	strncpy(to, from, to_length);
> -	if (from_length < to_length && !compatible) {
> -		/*
> -		 * space pad the string if it is short.
> -		 */
> -		memset(&to[from_length], ' ', to_length - from_length);
> +	if (compatible) {
> +		/* This zero-pads and nul-terminates the destination */
> +		ret = strscpy_pad(to, from, to_length);
> +	} else {
> +		/* no nul-termination but space-padding for short strings */
> +		size_t from_length = strlen(from);
> +		ret = from_length;
> +
> +		if (from_length > to_length) {
> +			from_length = to_length;
> +			ret = -E2BIG;
> +		}
> +
> +		memcpy(to, from, from_length);
> +
> +		if (from_length < to_length)
> +			memset(&to[from_length], ' ', to_length - from_length);
>  	}
> -	if (from_length > to_length)
> +
> +	if (ret < 0)
>  		 printk(KERN_WARNING "%s: %s string '%s' is too long\n",
>  			__func__, name, from);
>  }
> -- 
> 2.39.2
> 
Thanks
Justin