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Message-ID: <CAMuHMdU2c75WDCX+ptQgB7h0taHjG2pwL9db6gE3LKxv5Vz04Q@mail.gmail.com>
Date: Mon, 5 Feb 2024 13:47:08 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Kees Cook <keescook@...omium.org>
Cc: Andy Shevchenko <andy@...nel.org>, Justin Stitt <justinstitt@...gle.com>,
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 v2 2/4] string: Allow 2-argument strscpy()
Hi Kees,
On Mon, Feb 5, 2024 at 1:37 PM Kees Cook <keescook@...omium.org> wrote:
> Using sizeof(dst) for the "size" argument in strscpy() is the
> overwhelmingly common case. Instead of requiring this everywhere, allow a
> 2-argument version to be used that will use the sizeof() internally. There
> are other functions in the kernel with optional arguments[1], so this
> isn't unprecedented, and improves readability. Update and relocate the
> kern-doc for strscpy() too.
>
> Adjust ARCH=um build to notice the changed export name, as it doesn't
> do full header includes for the string helpers.
>
> This could additionally let us save a few hundred lines of code:
> 1177 files changed, 2455 insertions(+), 3026 deletions(-)
> with a treewide cleanup using Coccinelle:
>
> @needless_arg@
> expression DST, SRC;
> @@
>
> strscpy(DST, SRC
> -, sizeof(DST)
> )
>
> Link: https://elixir.bootlin.com/linux/v6.7/source/include/linux/pci.h#L1517 [1]
> 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>
Thanks for your patch!
> --- a/include/linux/string.h
> +++ b/include/linux/string.h
> +/*
> + * The 2 argument style can only be used when dst is an array with a
> + * known size.
> + */
> +#define __strscpy0(dst, src, ...) \
> + sized_strscpy(dst, src, sizeof(dst) + __must_be_array(dst))
> +#define __strscpy1(dst, src, size) sized_strscpy(dst, src, size)
(dst), (src), (size) etc.
> +
> +/**
> + * strscpy - Copy a C-string into a sized buffer
> + * @dst: Where to copy the string to
> + * @src: Where to copy the string from
> + * @...: Size of destination buffer (optional)
> + *
> + * Copy the source string @src, or as much of it as fits, into the
> + * destination @dst buffer. The behavior is undefined if the string
> + * buffers overlap. The destination @dst buffer is always NUL terminated,
> + * unless it's zero-sized.
> + *
> + * The size argument @... is only required when @dst is not an array, or
> + * when the copy needs to be smaller than sizeof(@dst).
> + *
> + * Preferred to strncpy() since it always returns a valid string, and
> + * doesn't unnecessarily force the tail of the destination buffer to be
> + * zero padded. If padding is desired please use strscpy_pad().
> + *
> + * Returns the number of characters copied in @dst (not including the
> + * trailing %NUL) or -E2BIG if @size is 0 or the copy from @src was
> + * truncated.
> + */
> +#define strscpy(dst, src, ...) \
> + CONCATENATE(__strscpy, COUNT_ARGS(__VA_ARGS__))(dst, src, __VA_ARGS__)
Likewise
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68korg
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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