netdev - Re: [PATCH] bonding: avoid adding slave device with IFF

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Date:   Tue, 22 Jun 2021 19:53:03 +0200
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     zhudi <zhudi21@...wei.com>, j.vosburgh@...il.com,
        vfalico@...il.com, kuba@...nel.org, davem@...emloft.net
Cc:     netdev@...r.kernel.org, rose.chen@...wei.com
Subject: Re: [PATCH] bonding: avoid adding slave device with IFF_MASTER flag



On 6/22/21 5:09 AM, zhudi wrote:
> From: Di Zhu <zhudi21@...wei.com>
> 
> The following steps will definitely cause the kernel to crash:
> 	ip link add vrf1 type vrf table 1
> 	modprobe bonding.ko max_bonds=1
> 	echo "+vrf1" >/sys/class/net/bond0/bonding/slaves
> 	rmmod bonding
> 
> The root cause is that: When the VRF is added to the slave device,
> it will fail, and some cleaning work will be done. because VRF device
> has IFF_MASTER flag, cleanup process  will not clear the IFF_BONDING flag.
> Then, when we unload the bonding module, unregister_netdevice_notifier()
> will treat the VRF device as a bond master device and treat netdev_priv()
> as struct bonding{} which actually is struct net_vrf{}.
> 
> By analyzing the processing logic of bond_enslave(), it seems that
> it is not allowed to add the slave device with the IFF_MASTER flag, so
> we need to add a code check for this situation.
> 
> Signed-off-by: Di Zhu <zhudi21@...wei.com>
> ---
>  drivers/net/bonding/bond_main.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
> index c5a646d06102..16840c9bc00d 100644
> --- a/drivers/net/bonding/bond_main.c
> +++ b/drivers/net/bonding/bond_main.c
> @@ -1601,6 +1601,12 @@ int bond_enslave(struct net_device *bond_dev, struct net_device *slave_dev,
>  	int link_reporting;
>  	int res = 0, i;
>  
> +	if (slave_dev->flags & IFF_MASTER) {

Missing NL_SET_ERR_MSG( ?

> +		netdev_err(bond_dev,
> +			   "Error: Device with IFF_MASTER cannot be enslaved\n");
> +		return -EPERM;
> +	}
> +
>  	if (!bond->params.use_carrier &&
>  	    slave_dev->ethtool_ops->get_link == NULL &&
>  	    slave_ops->ndo_do_ioctl == NULL) {
> 

This is strange, can you tell us why we keep the following lines after your patch ?

	if (bond_dev == slave_dev) {
		NL_SET_ERR_MSG(extack, "Cannot enslave bond to itself.");
		netdev_err(bond_dev, "cannot enslave bond to itself.\n");
		return -EPERM;
	}

I was under the impression that a stack of bonding devices was allowed.