io_uring: add missing lock in io_get_file_fixed

stable inclusion
from stable-v5.10.171
commit 08681391b84da27133deefaaddefd0acfa90c2be
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I6V7V1
CVE: CVE-2023-1872

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=08681391b84da27133deefaaddefd0acfa90c2be



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

io_get_file_fixed will access io_uring's context. Lock it if it is
invoked unlocked (eg via io-wq) to avoid a race condition with fixed
files getting unregistered.

No single upstream patch exists for this issue, it was fixed as part
of the file assignment changes that went into the 5.18 cycle.

Signed-off-by: Jheng, Bing-Jhong Billy <billy@starlabs.sg>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: ZhaoLong Wang <wangzhaolong1@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>