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

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Date:	Wed, 13 Apr 2011 11:44:48 -0400
From:	Chris Ball <cjb@...top.org>
To:	Greg Kroah-Hartman <gregkh@...e.de>
Cc:	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 Pisar wrote:
> On Wed, Apr 13, 2011 at 11:18:04AM -0400, Chris Ball wrote:
>> 
>> 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.
>> 
> This is on purpose to continue with code for case 2 as it prepares variables
> for cleaning visible part of display after the switch block.

Oops, sorry; I saw an imaginary break statement there.

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