vt: fix unicode buffer corruption when deleting characters

stable inclusion
from stable-v4.19.312
commit fc7dfe3d123f00e720be80b920da287810a1f37d
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I9Q994
CVE: CVE-2024-35823

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fc7dfe3d123f00e720be80b920da287810a1f37d



--------------------------------

commit 1581dafaf0d34bc9c428a794a22110d7046d186d upstream.

This is the same issue that was fixed for the VGA text buffer in commit
39cdb68c ("vt: fix memory overlapping when deleting chars in the
buffer"). The cure is also the same i.e. replace memcpy() with memmove()
due to the overlaping buffers.

Signed-off-by: Nicolas Pitre <nico@fluxnic.net>
Fixes: 81732c3b ("tty vt: Fix line garbage in virtual console on command line edition")
Cc: stable <stable@kernel.org>
Link: https://lore.kernel.org/r/sn184on2-3p0q-0qrq-0218-895349s4753o@syhkavp.arg


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Xiang Yang <xiangyang3@huawei.com>