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References: <20240205122916.it.909-kees@kernel.org> <20240205123525.1379299-3-keescook@chromium.org>
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From: Geert Uytterhoeven <geert@linux-m68k.org>
Date: Mon, 5 Feb 2024 13:48:51 +0100
Message-ID: <CAMuHMdXnW0ycz4y0m6d2yb_cAB4pjLmpveVBnL4sLNATtm388A@mail.gmail.com>
Subject: Re: [PATCH v2 3/4] string: Allow 2-argument strscpy_pad()
To: Kees Cook <keescook@chromium.org>
Cc: Andy Shevchenko <andy@kernel.org>, linux-hardening@vger.kernel.org, 
	Richard Weinberger <richard@nod.at>, Justin Stitt <justinstitt@google.com>, 
	Anton Ivanov <anton.ivanov@cambridgegreys.com>, Johannes Berg <johannes@sipsolutions.net>, 
	Willem de Bruijn <willemdebruijn.kernel@gmail.com>, Jason Wang <jasowang@redhat.com>, 
	kernel test robot <lkp@intel.com>, Nathan Chancellor <nathan@kernel.org>, 
	Azeem Shaikh <azeemshaikh38@gmail.com>, linux-kernel@vger.kernel.org, 
	linux-um@lists.infradead.org
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Hi Kees,

On Mon, Feb 5, 2024 at 1:36=E2=80=AFPM Kees Cook <keescook@chromium.org> wr=
ote:
> Similar to strscpy(), update strscpy_pad()'s 3rd argument to be
> optional when the destination is a compile-time known size array.
>
> Cc: Andy Shevchenko <andy@kernel.org>
> Cc: linux-hardening@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>

Thanks for your patch!

> --- a/include/linux/string.h
> +++ b/include/linux/string.h
> @@ -78,6 +78,10 @@ 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)

(dst) etc.

> @@ -123,17 +139,8 @@ 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 =3D (dest);                                          =
 \
> -       const char *__src =3D (src);                                     =
 \
> -       const size_t __count =3D (count);                                =
 \
> -       ssize_t __wrote;                                                \
> -                                                                       \
> -       __wrote =3D strscpy(__dst, __src, __count);                      =
 \
> -       if (__wrote >=3D 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, __V=
A_ARGS__)

Likewise,

Gr{oetje,eeting}s,

                        Geert

--=20
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k=
org

In personal conversations with technical people, I call myself a hacker. Bu=
t
when I'm talking to journalists I just say "programmer" or something like t=
hat.
                                -- Linus Torvalds