linux-kernel - [PATCH] vt: fix memory overlapping when deleting chars in the buffer

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Date:   Mon, 27 Jun 2022 18:29:40 +0800
From:   Yangxi Xiang <xyangxi5@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Johan Hovold <johan@...nel.org>,
        Igor Matheus Andrade Torrente <igormtorrente@...il.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        nick black <dankamongmen@...il.com>,
        Yangxi Xiang <xyangxi5@...il.com>
Subject: [PATCH] vt: fix memory overlapping when deleting chars in the buffer

A memory overlapping copy occurs when deleting a long line. Fix it by
using scr_memmovew.

Signed-off-by: Yangxi Xiang <xyangxi5@...il.com>
---
 drivers/tty/vt/vt.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index f8c87c4d7399..d87bff9d8ed5 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -853,9 +853,13 @@ static void insert_char(struct vc_data *vc, unsigned int nr)
 static void delete_char(struct vc_data *vc, unsigned int nr)
 {
 	unsigned short *p = (unsigned short *) vc->vc_pos;
+	unsigned short cp = (vc->vc_cols - vc->state.x - nr) * 2;
 
 	vc_uniscr_delete(vc, nr);
-	scr_memcpyw(p, p + nr, (vc->vc_cols - vc->state.x - nr) * 2);
+	if (cp > nr)
+		scr_memmovew(p, p + nr, cp);
+	else
+		scr_memcpyw(p, p + nr, cp);
 	scr_memsetw(p + vc->vc_cols - vc->state.x - nr, vc->vc_video_erase_char,
 			nr * 2);
 	vc->vc_need_wrap = 0;
-- 
2.17.1