bonding: hold ops lock around get_link

syzbot reports a case of ethtool_ops->get_link being called without
ops lock:

 ethtool_op_get_link+0x15/0x60 net/ethtool/ioctl.c:63
 bond_check_dev_link+0x1fb/0x4b0 drivers/net/bonding/bond_main.c:864
 bond_miimon_inspect drivers/net/bonding/bond_main.c:2734 [inline]
 bond_mii_monitor+0x49d/0x3170 drivers/net/bonding/bond_main.c:2956
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0xac3/0x18e0 kernel/workqueue.c:3319
 worker_thread+0x870/0xd50 kernel/workqueue.c:3400
 kthread+0x7b7/0x940 kernel/kthread.c:464
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:153
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Commit 04efcee ("net: hold instance lock during NETDEV_CHANGE")
changed to lockless __linkwatch_sync_dev in ethtool_op_get_link.
All paths except bonding are coming via locked ioctl. Add necessary
locking to bonding.

Reviewed-by: Hangbin Liu <[email protected]>
Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=48c14f61594bdfadb086
Fixes: 04efcee ("net: hold instance lock during NETDEV_CHANGE")
Signed-off-by: Stanislav Fomichev <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: Stanislav Fomichev

drivers/net/bonding/bond_main.c

@@ -850,8 +850,9 @@ static int bond_check_dev_link(struct bonding *bond,
 			       struct net_device *slave_dev, int reporting)
 {
 	const struct net_device_ops *slave_ops = slave_dev->netdev_ops;
-	struct ifreq ifr;
 	struct mii_ioctl_data *mii;
+	struct ifreq ifr;
+	int ret;
 
 	if (!reporting && !netif_running(slave_dev))
 		return 0;
@@ -860,9 +861,13 @@ static int bond_check_dev_link(struct bonding *bond,
 		return netif_carrier_ok(slave_dev) ? BMSR_LSTATUS : 0;
 
 	/* Try to get link status using Ethtool first. */
-	if (slave_dev->ethtool_ops->get_link)
-		return slave_dev->ethtool_ops->get_link(slave_dev) ?
-			BMSR_LSTATUS : 0;
+	if (slave_dev->ethtool_ops->get_link) {
+		netdev_lock_ops(slave_dev);
+		ret = slave_dev->ethtool_ops->get_link(slave_dev);
+		netdev_unlock_ops(slave_dev);
+
+		return ret ? BMSR_LSTATUS : 0;
+	}
 
 	/* Ethtool can't be used, fallback to MII ioctls. */
 	if (slave_ops->ndo_eth_ioctl) {