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

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Message-ID: <ba159a81-6dbc-d5a1-4682-b15517b49489@gmail.com>
Date:	Thu, 21 Jul 2016 14:53:37 +0200
From:	Jiri Slaby <jirislaby@...il.com>
To:	Petr Písař <ppisar@...hat.com>,
	Greg Kroah-Hartman <gregkh@...e.de>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, linux-kernel@...r.kernel.org,
	Artem Bityutskiy <dedekind1@...il.com>,
	Chris Ball <cjb@...top.org>,
	Daniel Taylor <Daniel.Taylor@....com>
Subject: Re: [PATCH] Clean console safely

On 04/15/2011, 10:08 AM, 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 PÃsaÅ <ppisar@...hat.com>
> ---
>  drivers/tty/vt/vt.c |    7 +++++++
>  1 files changed, 7 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> index 4bea1ef..cb661ca 100644
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -1197,6 +1197,13 @@ 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);

Why is here the division? I suppose this is superfluous, given
scr_memsetw proper divides the size, hm?

> +			set_origin(vc);
> +			if (CON_IS_VISIBLE(vc))
> +				update_screen(vc);
> +			/* fall through */
>  		case 2: /* erase whole display */
>  			count = vc->vc_cols * vc->vc_rows;
>  			start = (unsigned short *)vc->vc_origin;
> 


-- 
js