vt: fix memory overlapping when deleting chars in the buffer

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@kernel.org>
Signed-off-by: Yangxi Xiang <xyangxi5@gmail.com>
Link: https://lore.kernel.org/r/20220628093322.5688-1-xyangxi5@gmail.com
[ 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@broadcom.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 3e5088a17bbea5b6dbae3d17abc31dd91a546c04..abcacd377e09ba8d8368858e3b62a7e93935d2e7 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->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;