Received-SPF: pass (google.com: domain of linux-kernel+bounces-124108-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
Date: Thu, 28 Mar 2024 21:08:58 -0700
From: Kees Cook <keescook@chromium.org>
To: Justin Stitt <justinstitt@google.com>
Cc: Tyler Hicks <code@tyhicks.com>, ecryptfs@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] fs: ecryptfs: replace deprecated strncpy with strscpy
Message-ID: <202403282108.7FF7CE596C@keescook>
References: <20240321-strncpy-fs-ecryptfs-crypto-c-v1-1-d78b74c214ac@google.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20240321-strncpy-fs-ecryptfs-crypto-c-v1-1-d78b74c214ac@google.com>

On Thu, Mar 21, 2024 at 12:38:54AM +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. A good alternative is strscpy() as it guarantees
> NUL-termination on the destination buffer.
> 
> In crypto.c:
> We expect cipher_name to be NUL-terminated based on its use with
> the C-string format specifier %s and with other string apis like
> strlen():
> |	printk(KERN_ERR "Error attempting to initialize key TFM "
> |		"cipher with name = [%s]; rc = [%d]\n",
> |		tmp_tfm->cipher_name, rc);
> and
> |	int cipher_name_len = strlen(cipher_name);
> 
> In main.c:
> We can remove the manual NUL-byte assignments as well as the pointers to
> destinations (which I assume only existed to trim down on line length?)
> in favor of directly using the destination buffer which allows the
> compiler to get size information -- enabling the usage of the new
> 2-argument strscpy().
> 
> Note that this patch relies on the _new_ 2-argument versions of
> strscpy() and strscpy_pad() 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>

Looks correct. I don't see any need for padding.

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

-- 
Kees Cook