From: Petr Písař <ppisar@redhat.com>
Date: Fri, 15 Apr 2011 08:08:08 +0000 (+0200)
Subject: tty: Clean console safely
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=f8df13e0a901fe55631fed66562369b4dba40f8b;p=GitHub%2FLineageOS%2FG12%2Fandroid_kernel_amlogic_linux-4.9.git

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>
---

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;