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Date: Thu, 28 Mar 2024 21:05:29 -0700
From: Kees Cook <keescook@chromium.org>
To: Justin Stitt <justinstitt@google.com>
Cc: Michal Januszewski <spock@gentoo.org>, Helge Deller <deller@gmx.de>,
	linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org,
	linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] fbdev: uvesafb: replace deprecated strncpy with
 strscpy_pad
Message-ID: <202403282105.574E19BFA@keescook>
References: <20240320-strncpy-drivers-video-fbdev-uvesafb-c-v1-1-fd6af3766c80@google.com>
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In-Reply-To: <20240320-strncpy-drivers-video-fbdev-uvesafb-c-v1-1-fd6af3766c80@google.com>

On Wed, Mar 20, 2024 at 11:04:44PM +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.
> 
> We expect v86d_path to be NUL-terminated based on its use with the
> C-string format specifier in printf-likes:
> |	pr_err("failed to execute %s\n", v86d_path);
> and
> |	return snprintf(buf, PAGE_SIZE, "%s\n", v86d_path);
> 
> Let's also opt to pad v86d_path since it may get used in and around
> userspace:
> |	return call_usermodehelper(v86d_path, argv, envp, UMH_WAIT_PROC);
> 
> Considering the above, strscpy_pad() is the best replacement as it
> guarantees both NUL-termination and NUL-padding on the destination
> buffer.
> 
> 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
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@vger.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@google.com>

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

-- 
Kees Cook