io_uring/zcrx: call netdev_queue_get_dma_dev() under instance lock

netdev ops must be called under instance lock or rtnl_lock, but
io_register_zcrx_ifq() isn't doing this for netdev_queue_get_dma_dev().
Fix this by taking the instance lock using netdev_get_by_index_lock().

Extended the instance lock section to include attaching a memory
provider. Could not move io_zcrx_create_area() outside, since the dmabuf
codepath IORING_ZCRX_AREA_DMABUF requires ifq->dev.

Fixes: 59b8b32 ("io_uring/zcrx: add support for custom DMA devices")
Signed-off-by: David Wei <[email protected]>
Reviewed-by: Pavel Begunkov <[email protected]>
Reviewed-by: Jakub Kicinski <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>

Author: spikeh

io_uring/zcrx.c

@@ -620,29 +620,30 @@ int io_register_zcrx_ifq(struct io_ring_ctx *ctx,
 	if (ret)
 		goto err;
 
-	ifq->netdev = netdev_get_by_index(current->nsproxy->net_ns, reg.if_idx,
-					  &ifq->netdev_tracker, GFP_KERNEL);
+	ifq->netdev = netdev_get_by_index_lock(current->nsproxy->net_ns, reg.if_idx);
 	if (!ifq->netdev) {
 		ret = -ENODEV;
 		goto err;
 	}
+	netdev_hold(ifq->netdev, &ifq->netdev_tracker, GFP_KERNEL);
 
 	ifq->dev = netdev_queue_get_dma_dev(ifq->netdev, reg.if_rxq);
 	if (!ifq->dev) {
 		ret = -EOPNOTSUPP;
-		goto err;
+		goto netdev_put_unlock;
 	}
 	get_device(ifq->dev);
 
 	ret = io_zcrx_create_area(ifq, &area);
 	if (ret)
-		goto err;
+		goto netdev_put_unlock;
 
 	mp_param.mp_ops = &io_uring_pp_zc_ops;
 	mp_param.mp_priv = ifq;
-	ret = net_mp_open_rxq(ifq->netdev, reg.if_rxq, &mp_param);
+	ret = __net_mp_open_rxq(ifq->netdev, reg.if_rxq, &mp_param, NULL);
 	if (ret)
-		goto err;
+		goto netdev_put_unlock;
+	netdev_unlock(ifq->netdev);
 	ifq->if_rxq = reg.if_rxq;
 
 	reg.zcrx_id = id;
@@ -661,6 +662,9 @@ int io_register_zcrx_ifq(struct io_ring_ctx *ctx,
 		goto err;
 	}
 	return 0;
+netdev_put_unlock:
+	netdev_put(ifq->netdev, &ifq->netdev_tracker);
+	netdev_unlock(ifq->netdev);
 err:
 	scoped_guard(mutex, &ctx->mmap_lock)
 		xa_erase(&ctx->zcrx_ctxs, id);