linux-kernel - Re: [PATCH v3 3/4] string: Allow 2-argument strscpy

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Date: Wed, 7 Feb 2024 00:51:51 +0000
From: Justin Stitt <justinstitt@...gle.com>
To: Kees Cook <keescook@...omium.org>
Cc: Andy Shevchenko <andy@...nel.org>, linux-hardening@...r.kernel.org,
	Richard Weinberger <richard@....at>,
	Anton Ivanov <anton.ivanov@...bridgegreys.com>,
	Johannes Berg <johannes@...solutions.net>,
	Willem de Bruijn <willemdebruijn.kernel@...il.com>,
	Jason Wang <jasowang@...hat.com>, kernel test robot <lkp@...el.com>,
	Nathan Chancellor <nathan@...nel.org>,
	Azeem Shaikh <azeemshaikh38@...il.com>,
	linux-kernel@...r.kernel.org, linux-um@...ts.infradead.org
Subject: Re: [PATCH v3 3/4] string: Allow 2-argument strscpy_pad()

Hi,

On Tue, Feb 06, 2024 at 06:22:18AM -0800, Kees Cook wrote:
> Similar to strscpy(), update strscpy_pad()'s 3rd argument to be
> optional when the destination is a compile-time known size array.

This patch is diff'd against Patch 1/4 in this series, right? I wonder
why you split them up. If I hadn't literally just read that patch I
would be mildly confused.

I suppose one reason may be that 1/4 is a standalone change with a high
percentage chance of landing whilst this overloading magic may not land
as easily?

At any rate,
Reviewed-by: Justin Stitt <justinstitt@...gle.com>

>
> Cc: Andy Shevchenko <andy@...nel.org>
> Cc: linux-hardening@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  include/linux/string.h | 29 ++++++++++++++++++-----------
>  1 file changed, 18 insertions(+), 11 deletions(-)
>
> diff --git a/include/linux/string.h b/include/linux/string.h
> index 79b875de615e..9bd421ad92a4 100644
> --- a/include/linux/string.h
> +++ b/include/linux/string.h
> @@ -79,6 +79,10 @@ ssize_t sized_strscpy(char *, const char *, size_t);
>  	sized_strscpy(dst, src, sizeof(dst) + __must_be_array(dst))
>  #define __strscpy1(dst, src, size)	sized_strscpy(dst, src, size)
>
> +#define __strscpy_pad0(dst, src, ...)	\
> +	sized_strscpy_pad(dst, src, sizeof(dst) + __must_be_array(dst))
> +#define __strscpy_pad1(dst, src, size)	sized_strscpy_pad(dst, src, size)
> +
>  /**
>   * strscpy - Copy a C-string into a sized buffer
>   * @dst: Where to copy the string to
> @@ -104,6 +108,18 @@ ssize_t sized_strscpy(char *, const char *, size_t);
>  #define strscpy(dst, src, ...)	\
>  	CONCATENATE(__strscpy, COUNT_ARGS(__VA_ARGS__))(dst, src, __VA_ARGS__)
>
> +#define sized_strscpy_pad(dest, src, count)	({			\
> +	char *__dst = (dest);						\
> +	const char *__src = (src);					\
> +	const size_t __count = (count);					\
> +	ssize_t __wrote;						\
> +									\
> +	__wrote = sized_strscpy(__dst, __src, __count);			\
> +	if (__wrote >= 0 && __wrote < __count)				\
> +		memset(__dst + __wrote + 1, 0, __count - __wrote - 1);	\
> +	__wrote;							\
> +})
> +
>  /**
>   * strscpy_pad() - Copy a C-string into a sized buffer
>   * @dest: Where to copy the string to
> @@ -124,17 +140,8 @@ ssize_t sized_strscpy(char *, const char *, size_t);
>   * * The number of characters copied (not including the trailing %NULs)
>   * * -E2BIG if count is 0 or @src was truncated.
>   */
> -#define strscpy_pad(dest, src, count)	({			\
> -	char *__dst = (dest);						\
> -	const char *__src = (src);					\
> -	const size_t __count = (count);					\
> -	ssize_t __wrote;						\
> -									\
> -	__wrote = strscpy(__dst, __src, __count);			\
> -	if (__wrote >= 0 && __wrote < __count)				\
> -		memset(__dst + __wrote + 1, 0, __count - __wrote - 1);	\
> -	__wrote;							\
> -})
> +#define strscpy_pad(dst, src, ...)	\
> +	CONCATENATE(__strscpy_pad, COUNT_ARGS(__VA_ARGS__))(dst, src, __VA_ARGS__)
>
>  #ifndef __HAVE_ARCH_STRCAT
>  extern char * strcat(char *, const char *);
> --
> 2.34.1
>

Thanks
Justin