Re: [PATCH net] bonding: Fix warning in default_device_exit_batch()

[Nikolay Aleksandrov]

On 12/03/2023 17:21, Shigeru Yoshida wrote:
> syzbot reported warning in default_device_exit_batch() like below [1]:
> 
> WARNING: CPU: 1 PID: 56 at net/core/dev.c:10867 unregister_netdevice_many_notify+0x14cf/0x19f0 net/core/dev.c:10867
> ...
> Call Trace:
>  <TASK>
>  unregister_netdevice_many net/core/dev.c:10897 [inline]
>  default_device_exit_batch+0x451/0x5b0 net/core/dev.c:11350
>  ops_exit_list+0x125/0x170 net/core/net_namespace.c:174
>  cleanup_net+0x4ee/0xb10 net/core/net_namespace.c:613
>  process_one_work+0x9bf/0x1820 kernel/workqueue.c:2390
>  worker_thread+0x669/0x1090 kernel/workqueue.c:2537
>  kthread+0x2e8/0x3a0 kernel/kthread.c:376
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308
>  </TASK>
> 
> For bond devices which also has a master device, IFF_SLAVE flag is
> cleared at err_undo_flags label in bond_enslave() if it is not
> ARPHRD_ETHER type.  In this case, __bond_release_one() is not called
> when bond_netdev_event() received NETDEV_UNREGISTER event.  This
> causes the above warning.
> 
> This patch fixes this issue by setting IFF_SLAVE flag at
> err_undo_flags label in bond_enslave() if the bond device has a master
> device.
> 

The proper way is to check if the bond device had the IFF_SLAVE flag before the
ether_setup() call which clears it, and restore it after.

> Fixes: 7d5cd2ce5292 ("bonding: correctly handle bonding type change on enslave failure")
> Cc: Nikolay Aleksandrov <nikolay@xxxxxxxxxxxxxxxxxxx>
> Link: https://syzkaller.appspot.com/bug?id=391c7b1f6522182899efba27d891f1743e8eb3ef [1]
> Reported-by: syzbot+9dfc3f3348729cc82277@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Shigeru Yoshida <syoshida@xxxxxxxxxx>
> ---
>  drivers/net/bonding/bond_main.c | 2 ++
>  include/net/bonding.h           | 5 +++++
>  2 files changed, 7 insertions(+)
> 
> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
> index 00646aa315c3..1a8b59e1468d 100644
> --- a/drivers/net/bonding/bond_main.c
> +++ b/drivers/net/bonding/bond_main.c
> @@ -2291,6 +2291,8 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev,
>  			dev_close(bond_dev);
>  			ether_setup(bond_dev);
>  			bond_dev->flags |= IFF_MASTER;
> +			if (bond_has_master(bond))
> +				bond_dev->flags |= IFF_SLAVE;
>  			bond_dev->priv_flags &= ~IFF_TX_SKB_SHARING;
>  		}
>  	}
> diff --git a/include/net/bonding.h b/include/net/bonding.h
> index ea36ab7f9e72..ed0b49501fad 100644
> --- a/include/net/bonding.h
> +++ b/include/net/bonding.h
> @@ -57,6 +57,11 @@
>  
>  #define bond_has_slaves(bond) !list_empty(bond_slave_list(bond))
>  
> +/* master list primitives */
> +#define bond_master_list(bond) (&(bond)->dev->adj_list.upper)
> +
> +#define bond_has_master(bond) !list_empty(bond_master_list(bond))
> +

This is not the proper way to check for a master device.

>  /* IMPORTANT: bond_first/last_slave can return NULL in case of an empty list */
>  #define bond_first_slave(bond) \
>  	(bond_has_slaves(bond) ? \

The device flags are wrong because of ether_setup() which clears IFF_SLAVE, we should
just check if it was present before and restore it after the ether_setup() call.

I'll send a fix tomorrow after testing it.

Thanks,
 Nik