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

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Message-ID: <20110413152829.GB2993@dhcp-0-146.brq.redhat.com>
Date:	Wed, 13 Apr 2011 17:28:29 +0200
From:	Petr Pisar <ppisar@...hat.com>
To:	Chris Ball <cjb@...top.org>
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

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.

-- Petr
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