RDMA/iwcm: Fix a use-after-free related to destroying CM IDs

RDMA/iwcm: Fix a use-after-free related to destroying CM IDs

iw_conn_req_handler() associates a new struct rdma_id_private (conn_id) with
an existing struct iw_cm_id (cm_id) as follows:

        conn_id->cm_id.iw = cm_id;
        cm_id->context = conn_id;
        cm_id->cm_handler = cma_iw_handler;

rdma_destroy_id() frees both the cm_id and the struct rdma_id_private. Make
sure that cm_work_handler() does not trigger a use-after-free by only
freeing of the struct rdma_id_private after all pending work has finished.

Cc: stable@vger.kernel.org
Fixes: 59c68ac31e15 ("iw_cm: free cm_id resources on the last deref")
Reviewed-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Tested-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20240605145117.397751-6-bvanassche@acm.org
Signed-off-by: Leon Romanovsky <leon@kernel.org>