linux-hardening - Re: [PATCH] auxdisplay: panel: refactor deprecated strncpy

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Date:   Thu, 14 Sep 2023 20:18:44 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Willy Tarreau <willy@...roxy.com>,
        Ksenija Stanojevic <ksenija.stanojevic@...il.com>,
        Miguel Ojeda <ojeda@...nel.org>, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] auxdisplay: panel: refactor deprecated strncpy

On Mon, Sep 11, 2023 at 08:51:04PM +0000, Justin Stitt wrote:
> `strncpy` is deprecated and as such we should prefer more robust and
> less ambiguous interfaces.
> 
> In this case, all of `press_str`, `repeat_str` and `release_str` are
> explicitly marked as nonstring:
> |   struct {	/* valid when type == INPUT_TYPE_KBD */
> |           char press_str[sizeof(void *) + sizeof(int)] __nonstring;
> |           char repeat_str[sizeof(void *) + sizeof(int)] __nonstring;
> |           char release_str[sizeof(void *) + sizeof(int)] __nonstring;
> |   } kbd;
> 
> ... which makes `strtomem_pad` a suitable replacement as it is
> functionally the same whilst being more obvious about its behavior.

Yup, this is exactly what strtomem_pad() was made for. :)

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

-Kees

> 
> 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: Kees Cook <keescook@...omium.org>
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>
> ---
> Note: build-tested
> ---
>  drivers/auxdisplay/panel.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/auxdisplay/panel.c b/drivers/auxdisplay/panel.c
> index eba04c0de7eb..e20d35bdf5fe 100644
> --- a/drivers/auxdisplay/panel.c
> +++ b/drivers/auxdisplay/panel.c
> @@ -1449,10 +1449,9 @@ static struct logical_input *panel_bind_key(const char *name, const char *press,
>  	key->rise_time = 1;
>  	key->fall_time = 1;
>  
> -	strncpy(key->u.kbd.press_str, press, sizeof(key->u.kbd.press_str));
> -	strncpy(key->u.kbd.repeat_str, repeat, sizeof(key->u.kbd.repeat_str));
> -	strncpy(key->u.kbd.release_str, release,
> -		sizeof(key->u.kbd.release_str));
> +	strtomem_pad(key->u.kbd.press_str, press, '\0');
> +	strtomem_pad(key->u.kbd.repeat_str, repeat, '\0');
> +	strtomem_pad(key->u.kbd.release_str, release, '\0');
>  	list_add(&key->list, &logical_inputs);
>  	return key;
>  }
> 
> ---
> base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c
> change-id: 20230911-strncpy-drivers-auxdisplay-panel-c-83bce51f32cb
> 
> Best regards,
> --
> Justin Stitt <justinstitt@...gle.com>
> 

-- 
Kees Cook