linux-kernel - [PATCH] Clean console safely

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Message-Id: <1302854888-3606-1-git-send-email-ppisar@redhat.com>
Date:	Fri, 15 Apr 2011 10:08:08 +0200
From:	Petr Písař <ppisar@...hat.com>
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>,
	"Chris Ball" <cjb@...top.org>,
	"Daniel Taylor" <Daniel.Taylor@....com>,
	Petr Písař <ppisar@...hat.com>
Subject: [PATCH] Clean console safely

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 |    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);
+			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;
-- 
1.7.4.4

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