[PATCH] IB: fix CM use-after-free

If the CM REQ handling function gets to error2, then it frees
cm_id_priv->timewait_info.  But the next line goes through
ib_destroy_cm_id() -> ib_send_cm_rej() -> cm_reset_to_idle(),
which ends up calling cm_cleanup_timewait(), which dereferences the
pointer we just freed.  Make sure we clear cm_id_priv->timewait_info
after freeing it, so that doesn't happen.

Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/core/cm.c

@@ -1315,6 +1315,7 @@ error3:	atomic_dec(&cm_id_priv->refcount);
 	cm_deref_id(listen_cm_id_priv);
 	cm_cleanup_timewait(cm_id_priv->timewait_info);
 error2:	kfree(cm_id_priv->timewait_info);
+	cm_id_priv->timewait_info = NULL;
 error1:	ib_destroy_cm_id(&cm_id_priv->id);
 	return ret;
 }