linux-kernel - Re: [PATCH] Clean console safely

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Message-ID: <m38vvew577.fsf@pullcord.laptop.org>
Date:	Wed, 13 Apr 2011 11:18:04 -0400
From:	Chris Ball <cjb@...top.org>
To:	Petr Písař <ppisar@...hat.com>
Cc:	Greg Kroah-Hartman <gregkh@...e.de>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org,
	Artem Bityutskiy <dedekind1@...il.com>
Subject: Re: [PATCH] Clean console safely

Hi,

On Wed, Apr 13 2011, Petr Písař wrote:
> Traditional \E[2J sequence erases console display but scroll-back
> buffer and underlying device (frame) buffer keep data that can be
> accessed by scrolling console back.
>
> This patch introduce new \E[J parameter 3 that allows to scramble
> scroll-back buffer explicitly. Session locking programs (screen,
> vlock) can use it to prevent attacker to browse locked console
> history.
>
> Signed-off-by: Petr Písař <ppisar@...hat.com>
> ---
>  drivers/tty/vt/vt.c |    6 ++++++
>  1 files changed, 6 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> index 4bea1ef..fe96a1f 100644
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -1197,6 +1197,12 @@ static void csi_J(struct vc_data *vc, int vpar)
>  					      vc->vc_x + 1);
>  			}
>  			break;
> +		case 3: /* erase scroll-back buffer (and whole display) */
> +			scr_memsetw(vc->vc_screenbuf, vc->vc_video_erase_char,
> +				    vc->vc_screenbuf_size >> 1);
> +			set_origin(vc);
> +			if (CON_IS_VISIBLE(vc))
> +				update_screen(vc);
>  		case 2: /* erase whole display */
>  			count = vc->vc_cols * vc->vc_rows;
>  			start = (unsigned short *)vc->vc_origin;

Nitpick: the cases were ordered before -- 3 should go after 2.

- Chris.
-- 
Chris Ball   <cjb@...top.org>   <http://printf.net/>
One Laptop Per Child
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