Re: [PATCH v3 3/4] string: Allow 2-argument strscpy_pad()

[Justin Stitt <justinstitt@google.com>]

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@google.com>

>
> Cc: Andy Shevchenko <andy@kernel.org>
> Cc: linux-hardening@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.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