Re: [PATCH net] bonding: hold ops lock around get_link

[Hangbin Liu <liuhangbin@gmail.com>]

On Tue, Apr 08, 2025 at 10:14:51AM -0700, Stanislav Fomichev wrote:
> 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 04efcee6ef8d ("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.
> 
> Reported-by: syzbot+48c14f61594bdfadb086@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=48c14f61594bdfadb086
> Fixes: 04efcee6ef8d ("net: hold instance lock during NETDEV_CHANGE")
> Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
> ---
>  drivers/net/bonding/bond_main.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
> index 950d8e4d86f8..d1ec5ec6f7e5 100644
> --- a/drivers/net/bonding/bond_main.c
> +++ b/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 +861,14 @@ 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) ?
> +	if (slave_dev->ethtool_ops->get_link) {
> +		netdev_lock_ops(slave_dev);
> +		ret = slave_dev->ethtool_ops->get_link(slave_dev) ?
>  			BMSR_LSTATUS : 0;
> +		netdev_unlock_ops(slave_dev);
> +
> +		return ret;
> +	}
>  
>  	/* Ethtool can't be used, fallback to MII ioctls. */
>  	if (slave_ops->ndo_eth_ioctl) {
> -- 
> 2.49.0
> 

Reviewed-by: Hangbin Liu <liuhangbin@gmail.com>