ovl: fix use inode directly in rcu-walk mode

stable inclusion
from stable-v5.10.163
commit 740c537f52c1f54aff9094744483d1515c7c8b7b
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I6GCCV

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=740c537f52c1f54aff9094744483d1515c7c8b7b



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

commit 672e4268 upstream.

ovl_dentry_revalidate_common() can be called in rcu-walk mode.  As document
said, "in rcu-walk mode, d_parent and d_inode should not be used without
care".

Check inode here to protect access under rcu-walk mode.

Fixes: bccece1e ("ovl: allow remote upper")
Reported-and-tested-by:  <syzbot+a4055c78774bbf3498bb@syzkaller.appspotmail.com>
Signed-off-by: Chen Zhongjin <chenzhongjin@huawei.com>
Cc: <stable@vger.kernel.org> # v5.7
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Reviewed-by: Yang Erkun <yangerkun@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>