linux-hardening - Re: [PATCH] reiserfs: replace deprecated strncpy with scnprintf

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Date: Thu, 28 Mar 2024 15:06:03 -0700
From: Kees Cook <keescook@...omium.org>
To: Justin Stitt <justinstitt@...gle.com>
Cc: reiserfs-devel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH] reiserfs: replace deprecated strncpy with scnprintf

On Thu, Mar 28, 2024 at 09:16:52PM +0000, Justin Stitt wrote:
> strncpy() is deprecated for use on NUL-terminated destination strings
> [1] and as such we should prefer more robust and less ambiguous string
> interfaces.
> 
> Our goal here is to get @namebuf populated with @name's contents but
> surrounded with quotes. There is some careful handling done to ensure we
> properly truncate @name so that we have room for a literal quote as well
> as a NUL-term. All this careful handling can be done with scnprintf
> using the dynamic string width specifier %.*s which allows us to pass in
> the max size for a source string. Doing this, we can put literal quotes
> in our format specifier and ensure @name is truncated to fit inbetween
> these quotes (-3 is from 2 quotes + 1 NUL-byte).
> 
> All in all, we get to remove a deprecated use of strncpy and clean up
> this code nicely!
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@...r.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>

Yeah, I like the use of %.*s here. This is much more clear now I think.

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook