Subject: Re: [PATCH net v4] vlan: Propagate MAC address to VLANs

From: Mike Manning <[email-masked]>
Date: Mon, 9 May 2016 13:19:47 +0100

On 05/09/2016 07:48 AM, Michal Kubecek wrote:
> On Sat, May 07, 2016 at 11:00:09AM +0100, Mike Manning wrote:
>> The MAC address of the physical interface is only copied to the VLAN
>> when it is first created, resulting in an inconsistency after MAC
>> address changes of only newly created VLANs having an up-to-date MAC.
>>
>> The VLANs should continue inheriting the MAC address of the physical
>> interface until the VLAN MAC address is explicitly set to any value. 
>> This allows IPv6 EUI64 addresses for the VLAN to reflect any changes
>> to the MAC of the physical interface and thus for DAD to behave as
>> expected.
>>
>> Signed-off-by: Mike Manning <[email-masked]>
>> ---
>>  net/8021q/vlan.c     |    7 +++++++
>>  net/8021q/vlan_dev.c |   14 ++++++++++----
>>  2 files changed, 17 insertions(+), 4 deletions(-)
>>
>> --- a/net/8021q/vlan.c
>> +++ b/net/8021q/vlan.c
>> @@ -291,6 +291,12 @@ static void vlan_sync_address(struct net
>>  	if (ether_addr_equal(vlan->real_dev_addr, dev->dev_addr))
>>  		return;
>>  
>> +	/* vlan continues to inherit address of parent interface */
>> +	if (vlandev->addr_assign_type == NET_ADDR_STOLEN) {
>> +		ether_addr_copy(vlandev->dev_addr, dev->dev_addr);
>> +		goto out;
>> +	}
>> +
> 
> I might have missed something in the previous discussion but as
> ether_addr_copy() is just an optimized memcpy(), how is this going to
> handle the setups where the vlan device itself has an upper device? For
> example,
> 
>   - if it is a bridge port, how is the bridge going to learn about its
>     address change so that it can update its FDB?
>   - if it is a bond slave or team port, current code preserves the vlan
>     device address on real device change so everything is fine; your
>     proposal would change vlan device's address without bond being even
>     notified, I believe
>   - there might be a macvlan on top of the vlan and you might
>     accidentally match its address with the new one
>

Thanks for your review and this excellent catch. I will add address
notification for the vlan itself and test appropriately for when an upper
device is present.

>>  	/* vlan address was different from the old address and is equal to
>>  	 * the new address */
>>  	if (!ether_addr_equal(vlandev->dev_addr, vlan->real_dev_addr) &&
>> @@ -303,6 +309,7 @@ static void vlan_sync_address(struct net
>>  	    !ether_addr_equal(vlandev->dev_addr, dev->dev_addr))
>>  		dev_uc_add(dev, vlandev->dev_addr);
>>  
>> +out:
>>  	ether_addr_copy(vlan->real_dev_addr, dev->dev_addr);
>>  }
>>  
>> --- a/net/8021q/vlan_dev.c
>> +++ b/net/8021q/vlan_dev.c
>> @@ -255,9 +255,13 @@ static int vlan_dev_open(struct net_devi
>>  		return -ENETDOWN;
>>  
>>  	if (!ether_addr_equal(dev->dev_addr, real_dev->dev_addr)) {
>> -		err = dev_uc_add(real_dev, dev->dev_addr);
>> -		if (err < 0)
>> -			goto out;
>> +		if (dev->addr_assign_type == NET_ADDR_STOLEN) {
>> +			ether_addr_copy(dev->dev_addr, real_dev->dev_addr);
> 
> The same question here.
> 
>> +		} else {
>> +			err = dev_uc_add(real_dev, dev->dev_addr);
>> +			if (err < 0)
>> +				goto out;
>> +		}
>>  	}
>>  
>>  	if (dev->flags & IFF_ALLMULTI) {
>> @@ -558,8 +562,10 @@ static int vlan_dev_init(struct net_devi
>>  	/* ipv6 shared card related stuff */
>>  	dev->dev_id = real_dev->dev_id;
>>  
>> -	if (is_zero_ether_addr(dev->dev_addr))
>> +	if (is_zero_ether_addr(dev->dev_addr)) {
>>  		eth_hw_addr_inherit(dev, real_dev);
>> +		dev->addr_assign_type = NET_ADDR_STOLEN;
> 
> You might want to replace eth_hw_addr_inherit() with ether_addr_copy()
> here as they only differ in the former copying addr_assign_type which
> you are going to rewrite anyway. (But as both are most likely inlined,
> I would expect the resulting code to be the same in the end.)
> 
>                                                        Michal Kubecek
>

Thanks. Yes, I was aware of this but decided not to change it to keep the
changeset to a minimum. I will make the change as recommended.
 
>> +	}
>>  	if (is_zero_ether_addr(dev->broadcast))
>>  		memcpy(dev->broadcast, real_dev->broadcast, dev->addr_len);
>>
>> -- 
>> 1.7.10.4
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