linux-hardening - Re: [PATCH] string: Allow 2-argument strscpy()

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Message-ID: <CAHp75Veisrih_3Aj1TN=gX=d4+ebKOwnt3eUwATgAr+3x_iywg@mail.gmail.com>
Date: Wed, 31 Jan 2024 09:35:18 +0200
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Kees Cook <keescook@...omium.org>
Cc: Andy Shevchenko <andy@...nel.org>, Justin Stitt <justinstitt@...gle.com>, 
	linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] string: Allow 2-argument strscpy()

On Wed, Jan 31, 2024 at 7:53 AM 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.
>
> 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)
>         )

...

Shouldn't you include, if not yet, args.h to string.h?

...

> +/**
> + * 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().

For the sake of consistency shouldn't that be updated the same way?

> + * 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.
> + */

-- 
With Best Regards,
Andy Shevchenko