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: [email protected]
Fixes: 59c68ac ("iw_cm: free cm_id resources on the last deref")
Reviewed-by: Zhu Yanjun <[email protected]>
Tested-by: Shin'ichiro Kawasaki <[email protected]>
Signed-off-by: Bart Van Assche <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Leon Romanovsky <[email protected]>

Author: bvanassche

drivers/infiniband/core/iwcm.c

@@ -368,8 +368,10 @@ EXPORT_SYMBOL(iw_cm_disconnect);
  *
  * Clean up all resources associated with the connection and release
  * the initial reference taken by iw_create_cm_id.
+ *
+ * Returns true if and only if the last cm_id_priv reference has been dropped.
  */
-static void destroy_cm_id(struct iw_cm_id *cm_id)
+static bool destroy_cm_id(struct iw_cm_id *cm_id)
 {
 	struct iwcm_id_private *cm_id_priv;
 	struct ib_qp *qp;
@@ -439,7 +441,7 @@ static void destroy_cm_id(struct iw_cm_id *cm_id)
 		iwpm_remove_mapping(&cm_id->local_addr, RDMA_NL_IWCM);
 	}
 
-	(void)iwcm_deref_id(cm_id_priv);
+	return iwcm_deref_id(cm_id_priv);
 }
 
 /*
@@ -450,7 +452,8 @@ static void destroy_cm_id(struct iw_cm_id *cm_id)
  */
 void iw_destroy_cm_id(struct iw_cm_id *cm_id)
 {
-	destroy_cm_id(cm_id);
+	if (!destroy_cm_id(cm_id))
+		flush_workqueue(iwcm_wq);
 }
 EXPORT_SYMBOL(iw_destroy_cm_id);
 
@@ -1031,7 +1034,7 @@ static void cm_work_handler(struct work_struct *_work)
 		if (!test_bit(IWCM_F_DROP_EVENTS, &cm_id_priv->flags)) {
 			ret = process_event(cm_id_priv, &levent);
 			if (ret)
-				destroy_cm_id(&cm_id_priv->id);
+				WARN_ON_ONCE(destroy_cm_id(&cm_id_priv->id));
 		} else
 			pr_debug("dropping event %d\n", levent.event);
 		if (iwcm_deref_id(cm_id_priv))