tty: 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@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 7 insertions, 0 deletions

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index a48da2063060..b3915b7ad3e2 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -1193,6 +1193,13 @@ 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;