vt: fix memory overlapping when deleting chars in the buffer

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@kernel.org>
Signed-off-by: Yangxi Xiang <xyangxi5@gmail.com>
Link: https://lore.kernel.org/r/20220628093322.5688-1-xyangxi5@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index f8c87c4..dfc1f4b 100644 (file)
--- 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->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;