linux-hardening - Re: [PATCH] qlcnic: replace deprecated strncpy with strscpy

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Date: Sat, 14 Oct 2023 19:47:14 -0700
From: Kees Cook <keescook@...omium.org>
To: Justin Stitt <justinstitt@...gle.com>
Cc: Shahed Shaikh <shshaikh@...vell.com>,
	Manish Chopra <manishc@...vell.com>, GR-Linux-NIC-Dev@...vell.com,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH] qlcnic: replace deprecated strncpy with strscpy

On Thu, Oct 12, 2023 at 07:44:29PM +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.
> 
> We expect fw_info->fw_file_name to be NUL-terminated based on its use
> within _request_firmware_prepare() wherein `name` refers to it:
> |       if (firmware_request_builtin_buf(firmware, name, dbuf, size)) {
> |               dev_dbg(device, "using built-in %s\n", name);
> |               return 0; /* assigned */
> |       }
> ... and with firmware_request_builtin() also via `name`:
> |       if (strcmp(name, b_fw->name) == 0) {
> 
> There is no evidence that NUL-padding is required.
> 
> Considering the above, a suitable replacement is `strscpy` [2] due to
> the fact that it guarantees NUL-termination on the destination buffer
> without unnecessarily NUL-padding.

When doing the hard-coded value to sizeof(), can you include in the
commit log the rationale for it? For example:

  Additionally replace size macro (QLC_FW_FILE_NAME_LEN) with
  sizeof(fw_info->fw_file_name) to more directly tie the maximum buffer
  size to the destination buffer:

  struct qlc_83xx_fw_info {
          ...
          char    fw_file_name[QLC_FW_FILE_NAME_LEN];
  };


> 
> 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@...r.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>
> ---
> Note: build-tested only.
> 
> Found with: $ rg "strncpy\("
> ---
>  drivers/net/ethernet/qlogic/qlcnic/qlcnic_83xx_init.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/ethernet/qlogic/qlcnic/qlcnic_83xx_init.c b/drivers/net/ethernet/qlogic/qlcnic/qlcnic_83xx_init.c
> index c95d56e56c59..b733374b4dc5 100644
> --- a/drivers/net/ethernet/qlogic/qlcnic/qlcnic_83xx_init.c
> +++ b/drivers/net/ethernet/qlogic/qlcnic/qlcnic_83xx_init.c
> @@ -2092,8 +2092,8 @@ static int qlcnic_83xx_run_post(struct qlcnic_adapter *adapter)
>  		return -EINVAL;
>  	}
>  
> -	strncpy(fw_info->fw_file_name, QLC_83XX_POST_FW_FILE_NAME,
> -		QLC_FW_FILE_NAME_LEN);
> +	strscpy(fw_info->fw_file_name, QLC_83XX_POST_FW_FILE_NAME,
> +		sizeof(fw_info->fw_file_name));
>  
>  	ret = request_firmware(&fw_info->fw, fw_info->fw_file_name, dev);
>  	if (ret) {
> @@ -2396,12 +2396,12 @@ static int qlcnic_83xx_get_fw_info(struct qlcnic_adapter *adapter)
>  		switch (pdev->device) {
>  		case PCI_DEVICE_ID_QLOGIC_QLE834X:
>  		case PCI_DEVICE_ID_QLOGIC_QLE8830:
> -			strncpy(fw_info->fw_file_name, QLC_83XX_FW_FILE_NAME,
> -				QLC_FW_FILE_NAME_LEN);
> +			strscpy(fw_info->fw_file_name, QLC_83XX_FW_FILE_NAME,
> +				sizeof(fw_info->fw_file_name));
>  			break;
>  		case PCI_DEVICE_ID_QLOGIC_QLE844X:
> -			strncpy(fw_info->fw_file_name, QLC_84XX_FW_FILE_NAME,
> -				QLC_FW_FILE_NAME_LEN);
> +			strscpy(fw_info->fw_file_name, QLC_84XX_FW_FILE_NAME,
> +				sizeof(fw_info->fw_file_name));
>  			break;
>  		default:
>  			dev_err(&pdev->dev, "%s: Invalid device id\n",

But yes, this all looks right to me.

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook