linux-kernel - [PATCH 5.15 162/167] vt: fix memory overlapping when deleting chars in the buffer

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Message-Id: <20220719114712.152890944@linuxfoundation.org>
Date:   Tue, 19 Jul 2022 13:54:54 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, stable <stable@...nel.org>,
        Yangxi Xiang <xyangxi5@...il.com>
Subject: [PATCH 5.15 162/167] vt: fix memory overlapping when deleting chars in the buffer

From: Yangxi Xiang <xyangxi5@...il.com>

commit 39cdb68c64d84e71a4a717000b6e5de208ee60cc upstream.

A memory overlapping copy occurs when deleting a long line. This memory
overlapping copy can cause data corruption when scr_memcpyw is optimized
to memcpy because memcpy does not ensure its behavior if the destination
buffer overlaps with the source buffer. The line buffer is not always
broken, because the memcpy utilizes the hardware acceleration, whose
result is not deterministic.

Fix this problem by using replacing the scr_memcpyw with scr_memmovew.

Fixes: 81732c3b2fed ("tty vt: Fix line garbage in virtual console on command line edition")
Cc: stable <stable@...nel.org>
Signed-off-by: Yangxi Xiang <xyangxi5@...il.com>
Link: https://lore.kernel.org/r/20220628093322.5688-1-xyangxi5@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/tty/vt/vt.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -855,7 +855,7 @@ static void delete_char(struct vc_data *
 	unsigned short *p = (unsigned short *) vc->vc_pos;
 
 	vc_uniscr_delete(vc, nr);
-	scr_memcpyw(p, p + nr, (vc->vc_cols - vc->state.x - nr) * 2);
+	scr_memmovew(p, p + nr, (vc->vc_cols - vc->state.x - nr) * 2);
 	scr_memsetw(p + vc->vc_cols - vc->state.x - nr, vc->vc_video_erase_char,
 			nr * 2);
 	vc->vc_need_wrap = 0;