Received-SPF: pass (google.com: domain of linux-kernel+bounces-163083-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Date: Mon, 29 Apr 2024 14:58:25 -0700
From: Kees Cook <keescook@chromium.org>
To: Justin Stitt <justinstitt@google.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>,
	Len Brown <len.brown@intel.com>, Pavel Machek <pavel@ucw.cz>,
	linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-hardening@vger.kernel.org
Subject: Re: [PATCH] PM: hibernate: replace deprecated strncpy with strscpy
Message-ID: <202404291457.8E79DC5@keescook>
References: <20240429-strncpy-kernel-power-hibernate-c-v1-1-8688f492d3e6@google.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20240429-strncpy-kernel-power-hibernate-c-v1-1-8688f492d3e6@google.com>

On Mon, Apr 29, 2024 at 08:50:30PM +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.
> 
> This kernel config option is simply assigned with the resume_file
> buffer. It should be NUL-terminated but not necessarily NUL-padded as
> per its further usage with other string apis:
> |	static int __init find_resume_device(void)
> |	{
> |		if (!strlen(resume_file))
> |			return -ENOENT;
> |
> |		pm_pr_dbg("Checking hibernation image partition %s\n", resume_file);
> 
> Use strscpy [2] as it guarantees NUL-termination on the destination
> buffer. Specifically, use the new 2-argument version of strscpy()
> introduced in Commit e6584c3964f2f ("string: Allow 2-argument
> strscpy()").
> 
> 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@vger.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@google.com>
> ---
> Note: build-tested only.
> 
> Found with: $ rg "strncpy\("
> ---
>  kernel/power/hibernate.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
> index 43b1a82e800c..0a213f69a9e4 100644
> --- a/kernel/power/hibernate.c
> +++ b/kernel/power/hibernate.c
> @@ -1361,7 +1361,7 @@ static int __init resume_setup(char *str)
>  	if (noresume)
>  		return 1;
>  
> -	strncpy(resume_file, str, 255);
> +	strscpy(resume_file, str);
>  	return 1;
>  }
>  

Yup, this looks correct to me. resume_file is:

static char resume_file[256] = CONFIG_PM_STD_PARTITION;

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

-- 
Kees Cook