linux-kernel - Re: [PATCH v2] drm/modes: replace deprecated strncpy with strscpy

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Message-ID: <202310181651.E47F9E32@keescook>
Date:   Wed, 18 Oct 2023 16:51:28 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org, Xu Panda <xu.panda@....com.cn>
Subject: Re: [PATCH v2] drm/modes: replace deprecated strncpy with strscpy_pad

On Mon, Oct 16, 2023 at 10:38:20PM +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 should NUL-pad as there are full struct copies happening in places:
> |       struct drm_mode_modeinfo umode;
> |
> |       ...
> |               struct drm_property_blob *blob;
> |
> |               drm_mode_convert_to_umode(&umode, mode);
> |               blob = drm_property_create_blob(crtc->dev,
> |                                               sizeof(umode), &umode);
> 
> A suitable replacement is `strscpy_pad` due to the fact that it
> guarantees both NUL-termination and NUL-padding on the destination
> buffer.
> 
> Additionally, replace size macro `DRM_DISPLAY_MODE_LEN` with sizeof() to
> more directly tie the maximum buffer size to the destination buffer:
> |       struct drm_display_mode {
> |               ...
> |       	char name[DRM_DISPLAY_MODE_LEN];
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@...r.kernel.org
> Cc: Xu Panda <xu.panda@....com.cn>
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>

Thanks for the respin; this looks good to me.

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

-- 
Kees Cook