[PATCH] Clean console safely

["Petr Písař" <ppisar@redhat.com>]

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.
---
 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 147ede3..c31bf2a 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -1198,6 +1198,12 @@ 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;
-- 
1.7.4