!1844 net: vmxnet3: fix possible NULL pointer dereference in vmxnet3_rq_cleanup()

Merge Pull Request from: @ci-robot 
 
PR sync from: Zhengchao Shao <shaozhengchao@huawei.com>
https://mailweb.openeuler.org/hyperkitty/list/kernel@openeuler.org/message/G5OSD5RLARLR4R7GJ3EUB6LG6ONKAZ46/ 
 
https://gitee.com/src-openeuler/kernel/issues/I7UWI8 
 
Link:https://gitee.com/openeuler/kernel/pulls/1844 

Reviewed-by: Yue Haibing <yuehaibing@huawei.com> 
Signed-off-by: Liu YongQiang <liuyongqiang13@huawei.com> 

drivers/net/vmxnet3/vmxnet3_drv.c

@@ -1586,6 +1586,10 @@ vmxnet3_rq_cleanup(struct vmxnet3_rx_queue *rq,
 	u32 i, ring_idx;
 	struct Vmxnet3_RxDesc *rxd;
 
+	/* ring has already been cleaned up */
+	if (!rq->rx_ring[0].base)
+		return;
+
 	for (ring_idx = 0; ring_idx < 2; ring_idx++) {
 		for (i = 0; i < rq->rx_ring[ring_idx].size; i++) {
 #ifdef __BIG_ENDIAN_BITFIELD