netdev - Re: [PATCH net] rtnetlink: allow to set iface down before enslaving it

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Date: Tue, 2 Jan 2024 13:14:21 +0100
From: Nicolas Dichtel <nicolas.dichtel@...nd.com>
To: Phil Sutter <phil@....cc>, "David S . Miller" <davem@...emloft.net>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Eric Dumazet <edumazet@...gle.com>, David Ahern <dsahern@...nel.org>,
 netdev@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH net] rtnetlink: allow to set iface down before enslaving
 it

Le 01/01/2024 à 23:10, Phil Sutter a écrit :
> On Fri, Dec 29, 2023 at 11:08:35AM +0100, Nicolas Dichtel wrote:
>> The below commit adds support for:
>>> ip link set dummy0 down
>>> ip link set dummy0 master bond0 up
>>
>> but breaks the opposite:
>>> ip link set dummy0 up
>>> ip link set dummy0 master bond0 down
>>
>> Let's add a workaround to have both commands working.
>>
>> Cc: stable@...r.kernel.org
>> Fixes: a4abfa627c38 ("net: rtnetlink: Enslave device before bringing it up")
>> Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>
>> ---
>>  net/core/rtnetlink.c | 8 ++++++++
>>  1 file changed, 8 insertions(+)
>>
>> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
>> index e8431c6c8490..dd79693c2d91 100644
>> --- a/net/core/rtnetlink.c
>> +++ b/net/core/rtnetlink.c
>> @@ -2905,6 +2905,14 @@ static int do_setlink(const struct sk_buff *skb,
>>  		call_netdevice_notifiers(NETDEV_CHANGEADDR, dev);
>>  	}
>>  
>> +	/* Backward compat: enable to set interface down before enslaving it */
>> +	if (!(ifm->ifi_flags & IFF_UP) && ifm->ifi_change & IFF_UP) {
>> +		err = dev_change_flags(dev, rtnl_dev_combine_flags(dev, ifm),
>> +				       extack);
>> +		if (err < 0)
>> +			goto errout;
>> +	}
>> +
>>  	if (tb[IFLA_MASTER]) {
>>  		err = do_set_master(dev, nla_get_u32(tb[IFLA_MASTER]), extack);
>>  		if (err)
> 
> Doesn't this merely revert to the old behaviour of setting the interface
> up before enslaving if both IFF_UP and IFLA_MASTER are present? Did you
> test this with a bond-type master?
Yes, both command sequences (cf commit log) work after the patch.
dev_change_flags() is called before do_set_master() only if the user asks to
remove the flag IFF_UP.


Regards,
Nicolas