linux-kernel - Re: [PATCH] crypto: qat - use strscpy_pad to simplify buffer initialization

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Message-ID: <aPkfsuliKYy5UAbB@smile.fi.intel.com>
Date: Wed, 22 Oct 2025 21:17:22 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Thorsten Blum <thorsten.blum@...ux.dev>
Cc: Giovanni Cabiddu <giovanni.cabiddu@...el.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>,
	Jack Xu <jack.xu@...el.com>,
	Suman Kumar Chakraborty <suman.kumar.chakraborty@...el.com>,
	Qianfeng Rong <rongqianfeng@...o.com>, qat-linux@...el.com,
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] crypto: qat - use strscpy_pad to simplify buffer
 initialization

On Wed, Oct 22, 2025 at 02:36:19PM +0200, Thorsten Blum wrote:
> Use strscpy_pad() to copy the string and zero-pad the destination buffer
> in a single step instead of zero-initializing the buffer first and then
> immediately overwriting it using strscpy().
> 
> Replace the magic number 16 with sizeof(buf) and remove the redundant
> parentheses around kstrtoul() while we're at it.

I understand that you focused on strscpy*() conversions, but the below I think
needs a bigger refactoring, see my remarks.

...

> -	char buf[16] = {0};
> +	char buf[16] = {};
>  	unsigned long ae = 0;
>  	int i;
>  
> -	strscpy(buf, str, sizeof(buf));
> -	for (i = 0; i < 16; i++) {
> +	strscpy_pad(buf, str);

First of all, why do we need a _pad() version here? Is the data somehow being
used as a whole?

> +	for (i = 0; i < sizeof(buf); i++) {
>  		if (!isdigit(buf[i])) {
>  			buf[i] = '\0';
>  			break;
>  		}
>  	}
> -	if ((kstrtoul(buf, 10, &ae)))
> +	if (kstrtoul(buf, 10, &ae))
>  		return -EFAULT;

Looking at this, it tries to work around the kstrtoul() inability to perform
partial parses. Instead, this should do something like

	unsigned long long x;
	const char *end;

	simple_strtoull(...);
	if (x > UINT_MAX || end == buf)
		return $ERR; // wrong input / overflow

-- 
With Best Regards,
Andy Shevchenko