linux-hardening - Re: [PATCH] crypto: qat - refactor deprecated strncpy

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Date:   Thu, 14 Sep 2023 20:40:20 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Giovanni Cabiddu <giovanni.cabiddu@...el.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>, qat-linux@...el.com,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] crypto: qat - refactor deprecated strncpy

On Wed, Sep 13, 2023 at 12:51:05AM +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> 
> We should prefer more robust and less ambiguous string interfaces.
> 
> `buf` is expected to be NUL-terminated for its eventual use in
> `kstrtoul()` and NUL-padding is not required.
> 
> Due to the above, a suitable replacement is `strscpy` [2] due to the
> fact that it guarantees NUL-termination on the destination buffer.
> 
> 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.
> ---
>  drivers/crypto/intel/qat/qat_common/qat_uclo.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/crypto/intel/qat/qat_common/qat_uclo.c b/drivers/crypto/intel/qat/qat_common/qat_uclo.c
> index ce837bcc1cab..e2f82128043e 100644
> --- a/drivers/crypto/intel/qat/qat_common/qat_uclo.c
> +++ b/drivers/crypto/intel/qat/qat_common/qat_uclo.c
> @@ -200,7 +200,7 @@ static int qat_uclo_parse_num(char *str, unsigned int *num)
>  	unsigned long ae = 0;
>  	int i;
>  
> -	strncpy(buf, str, 15);
> +	strscpy(buf, str, sizeof(buf));
>  	for (i = 0; i < 16; i++) {
>  		if (!isdigit(buf[i])) {

I was initially worried when I saw this walking the entire contents, but
I see it is explicitly zeroed on the stack first, so this is fine:

        char buf[16] = {0};


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

-Kees

>  			buf[i] = '\0';
> 
> ---
> base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c
> change-id: 20230913-strncpy-drivers-crypto-intel-qat-qat_common-qat_uclo-c-0f4b16830f59
> 
> Best regards,
> --
> Justin Stitt <justinstitt@...gle.com>
> 

-- 
Kees Cook