RE: [PATCH] Clean console safely

["Daniel Taylor" <Daniel.Taylor@wdc.com>]

 

> -----Original Message-----
> From: linux-kernel-owner@vger.kernel.org 
> [mailto:linux-kernel-owner@vger.kernel.org] On Behalf Of Chris Ball
> Sent: Wednesday, April 13, 2011 8:45 AM
> To: Greg Kroah-Hartman
> Cc: Alan Cox; linux-kernel@vger.kernel.org; Artem Bityutskiy
> 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@redhat.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.

Shouldn't there be a "/* fall through */", or similar, comment,
or all of the existing ones in the kernel extraneous?  Personally,
I prefer to see clearly that the missing "break" is intentional.

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