Re: [PATCH] i40e: use scnprintf over strncpy+strncat

[Justin Stitt]

On Tue, Oct 10, 2023 at 08:53:00PM +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.
>
> Moreover, `strncat` shouldn't really be used either as per
> fortify-string.h:
>  * Do not use this function. While FORTIFY_SOURCE tries to avoid
>  * read and write overflows, this is only possible when the sizes
>  * of @p and @q are known to the compiler. Prefer building the
>  * string with formatting, via scnprintf() or similar.
>
> Instead, use `scnprintf` with "%s%s" format string. This code is now
> more readable and robust.
>
> 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@xxxxxxxxxxxxxxx
> Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx>
> ---
> Note: build-tested only.
> ---
>  drivers/net/ethernet/intel/i40e/i40e_ddp.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_ddp.c b/drivers/net/ethernet/intel/i40e/i40e_ddp.c
> index 0e72abd178ae..ec25e4be250f 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_ddp.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_ddp.c
> @@ -438,10 +438,9 @@ int i40e_ddp_flash(struct net_device *netdev, struct ethtool_flash *flash)
>  		char profile_name[sizeof(I40E_DDP_PROFILE_PATH)
>  				  + I40E_DDP_PROFILE_NAME_MAX];
>
> -		profile_name[sizeof(profile_name) - 1] = 0;
> -		strncpy(profile_name, I40E_DDP_PROFILE_PATH,
> -			sizeof(profile_name) - 1);
> -		strncat(profile_name, flash->data, I40E_DDP_PROFILE_NAME_MAX);
> +		scnprintf(profile_name, sizeof(profile_name), "%s%s",
> +			  I40E_DDP_PROFILE_PATH, flash->data);
> +
>  		/* Load DDP recipe. */
>  		status = request_firmware(&ddp_config, profile_name,
>  					  &netdev->dev);
>
> ---
> base-commit: cbf3a2cb156a2c911d8f38d8247814b4c07f49a2
> change-id: 20231010-strncpy-drivers-net-ethernet-intel-i40e-i40e_ddp-c-dd7f20b7ed5d
>
> Best regards,
> --
> Justin Stitt <justinstitt@xxxxxxxxxx>
>
Hi, this patch was bundled up with some others. It has a new home:

https://lore.kernel.org/all/20231010-netdev-replace-strncpy-resend-as-series-v1-0-caf9f0f2f021@xxxxxxxxxx/