linux-kernel - [PATCH v4.19-v5.4] vt: fix memory overlapping when deleting chars in the buffer

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Message-Id: <20240329191208.88821-1-kuntal.nayak@broadcom.com>
Date: Fri, 29 Mar 2024 12:12:08 -0700
From: Kuntal Nayak <kuntal.nayak@...adcom.com>
To: stable@...r.kernel.org,
	gregkh@...uxfoundation.org
Cc: jslaby@...e.com,
	linux-kernel@...r.kernel.org,
	ajay.kaher@...adcom.com,
	alexey.makhalov@...adcom.com,
	vasavi.sirnapalli@...adcom.com,
	Yangxi Xiang <xyangxi5@...il.com>,
	stable <stable@...nel.org>,
	Kuntal Nayak <kuntal.nayak@...adcom.com>
Subject: [PATCH v4.19-v5.4] vt: fix memory overlapping when deleting chars in the buffer

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

[ upstream commit 39cdb68c64d8 ]

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>
[ KN: vc_state is not a separate structure in LTS v4.19, v5.4. Adjusted the patch
  accordingly by using vc_x instead of state.x for backport. ]
Signed-off-by: Kuntal Nayak <kuntal.nayak@...adcom.com>
---
 drivers/tty/vt/vt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index c9083d853..a351e264d 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -855,7 +855,7 @@ static void delete_char(struct vc_data *vc, unsigned int nr)
 	unsigned short *p = (unsigned short *) vc->vc_pos;
 
 	vc_uniscr_delete(vc, nr);
-	scr_memcpyw(p, p + nr, (vc->vc_cols - vc->vc_x - nr) * 2);
+	scr_memmovew(p, p + nr, (vc->vc_cols - vc->vc_x - nr) * 2);
 	scr_memsetw(p + vc->vc_cols - vc->vc_x - nr, vc->vc_video_erase_char,
 			nr * 2);
 	vc->vc_need_wrap = 0;
-- 
2.39.0