linux-kernel - Re: [PATCH] tomoyo: refactor deprecated strncpy

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Message-ID: <202308040039.D9B575B3F@keescook>
Date:   Fri, 4 Aug 2023 00:40:15 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Kentaro Takeda <takedakn@...data.co.jp>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Paul Moore <paul@...l-moore.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] tomoyo: refactor deprecated strncpy

On Thu, Aug 03, 2023 at 09:33:44PM +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> 
> A suitable replacement is `strscpy` [2] due to the fact that it
> guarantees NUL-termination on its destination buffer argument which is
> _not_ the case for `strncpy`!
> 
> It should be noted that the destination buffer is zero-initialized and
> had a max length of `sizeof(dest) - 1`. There is likely _not_ a bug
> present in the current implementation. However, by switching to
> `strscpy` we get the benefit of no longer needing the `- 1`'s from the
> string copy invocations on top of `strscpy` being a safer interface all
> together.
> 
> [1]: www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
> [2]: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html
> 
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@...r.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>

Thanks! This looks correct to me.

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

-- 
Kees Cook