net: designate queue counts as "double ops protected" by instance lock

Drivers which opt into instance lock protection of ops should
only call set_real_num_*_queues() under the instance lock.
This means that queue counts are double protected (writes
are under both rtnl_lock and instance lock, readers under
either).

Some readers may still be under the rtnl_lock, however, so for
now we need double protection of writers.

OTOH queue API paths are only under the protection of the instance
lock, so we need to validate that the instance is actually locking
ops, otherwise the input checks we do against queue count are racy.

Acked-by: Stanislav Fomichev <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: kuba-moo

include/linux/netdevice.h

@@ -2523,6 +2523,9 @@ struct net_device {
 	 * Double protects:
 	 *	@up
 	 *
+	 * Double ops protects:
+	 *	@real_num_rx_queues, @real_num_tx_queues
+	 *
 	 * Also protects some fields in struct napi_struct.
 	 *
 	 * Ordering: take after rtnl_lock.

net/core/dev.c

@@ -3130,6 +3130,7 @@ int netif_set_real_num_tx_queues(struct net_device *dev, unsigned int txq)
 	if (dev->reg_state == NETREG_REGISTERED ||
 	    dev->reg_state == NETREG_UNREGISTERING) {
 		ASSERT_RTNL();
+		netdev_ops_assert_locked(dev);
 
 		rc = netdev_queue_update_kobjects(dev, dev->real_num_tx_queues,
 						  txq);
@@ -3179,6 +3180,7 @@ int netif_set_real_num_rx_queues(struct net_device *dev, unsigned int rxq)
 
 	if (dev->reg_state == NETREG_REGISTERED) {
 		ASSERT_RTNL();
+		netdev_ops_assert_locked(dev);
 
 		rc = net_rx_queue_update_kobjects(dev, dev->real_num_rx_queues,
 						  rxq);

net/core/net-sysfs.c

@@ -2148,8 +2148,10 @@ static void remove_queue_kobjects(struct net_device *dev)
 	net_rx_queue_update_kobjects(dev, real_rx, 0);
 	netdev_queue_update_kobjects(dev, real_tx, 0);
 
+	netdev_lock_ops(dev);
 	dev->real_num_rx_queues = 0;
 	dev->real_num_tx_queues = 0;
+	netdev_unlock_ops(dev);
 #ifdef CONFIG_SYSFS
 	kset_unregister(dev->queues_kset);
 #endif

net/core/netdev-genl.c

@@ -867,6 +867,13 @@ int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info)
 		goto err_unlock_sock;
 	}
 
+	if (!netdev_need_ops_lock(netdev)) {
+		err = -EOPNOTSUPP;
+		NL_SET_BAD_ATTR(info->extack,
+				info->attrs[NETDEV_A_DEV_IFINDEX]);
+		goto err_unlock;
+	}
+
 	if (dev_xdp_prog_count(netdev)) {
 		NL_SET_ERR_MSG(info->extack, "unable to bind dmabuf to device with XDP program attached");
 		err = -EEXIST;

net/core/netdev_rx_queue.c

@@ -92,6 +92,9 @@ static int __net_mp_open_rxq(struct net_device *dev, unsigned ifq_idx,
 	struct netdev_rx_queue *rxq;
 	int ret;
 
+	if (!netdev_need_ops_lock(dev))
+		return -EOPNOTSUPP;
+
 	if (ifq_idx >= dev->real_num_rx_queues)
 		return -EINVAL;
 	ifq_idx = array_index_nospec(ifq_idx, dev->real_num_rx_queues);